Attention-deficit Hyperactivity Disorder

Attention-deficit hyperactivity disorder is a neurodevelopmental disorder characterized by persistent patterns of inattention, hyperactivity, and impulsivity that impair functioning across multiple settings.

Exam domain	One-glance essentials
Definition / diagnosis	Neurodevelopmental disorder of developmentally excessive inattention and/or hyperactivity-impulsivity ^[1] Symptoms begin in childhood and impair more than one setting ^[1]
Epidemiology / risks	High heritability, prematurity and prenatal exposures contribute ^[1] Learning, language, autism and tic disorders commonly coexist ^[1]
Core mechanism	Frontostriatal and catecholamine-network differences impair executive control ^[1] Environmental demands expose deficits as tasks become complex ^[1]
Clinical picture	Distractibility, disorganisation, impulsivity and excessive activity ^[1] Girls may present predominantly inattentive and be missed ^[1]
Investigations	Clinical diagnosis uses developmental history and multi-informant reports ^[2] Screen hearing, vision, sleep, learning, mood and safeguarding; no diagnostic blood test exists ^[2]
Management	Parent/teacher strategies and educational adjustments are foundational ^[3] Stimulants or atomoxetine/guanfacine are chosen with monitoring and shared decisions ^[3]
Complications	Academic failure, injury, low self-esteem and family conflict ^[4] Substance misuse and mood disorders increase later risk ^[4]
Prevention / follow-up	Early school support and consistent routines reduce impairment ^[3] Monitor growth, pulse, blood pressure, sleep and diversion during medication ^[3]
Exam traps	*Symptoms must occur across settings, not only in one classroom* ^[2] Treating ADHD does not cause addiction when medication is appropriately supervised ^[3]

References

^[1] Senior notes: ryanho-psych.md (Section 12.3 - summary table of childhood psychiatric disorders)

^[2] Senior notes: ryanho-psych.md (Section 12.3 — summary table of childhood psychiatric disorders)

^[3] Senior notes: ryanho-psych.md (Section 12.3 — Attention-deficit Hyperactivity Disorder: management approach, medications, non-pharmacological interventions; Section 12.4 — ODD/CD management including treatment of comorbid ADHD)

^[4] Senior notes: ryanho-psych.md (Section 12.3 — Attention-deficit Hyperactivity Disorder: clinical features and functional impairment, course and prognosis, medications and side effects; Section 12.4 — ODD/CD course and prognosis)

Attention-Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterised by a persistent pattern of inattention and/or hyperactivity-impulsivity that is developmentally inappropriate, pervasive across settings, and causes clinically significant functional impairment ^[1]^[2].

Let's break down the name:

"Attention-deficit" → the core cognitive problem is a deficit in sustaining and directing attention
"Hyperactivity" → "hyper" (Greek: excessive) + "activity" → excessive motor restlessness
"Disorder" → a syndrome causing functional impairment, not just a personality trait

The key conceptual point: ADHD is not about a child being "naughty" or "lazy." It reflects neurobiological dysfunction in frontal-subcortical circuits governing executive functions — particularly inhibitory control, working memory, and attentional regulation. Think of it as the brain's "braking system" and "prioritisation system" being underactive ^[2].

Symptoms are characterized by deficits in both (ICD-10) or one (DSM-5) of: Hyperactivity/impulsivity (usually presents earlier → due to executive inhibition deficits) and Inattention (usually presents later, in school age → due to deficient attention mechanisms). Symptoms are developmentally inappropriate and occur across several settings. Symptoms emerge early by age of 12y (DSM-5) or 6y (ICD-10). ^[1]^[2]

ICD-10 vs DSM-5 Terminology

ICD-10 uses the term "Hyperkinetic Disorder" (F90) and requires both inattention and hyperactivity to be present. DSM-5 uses "ADHD" and allows diagnosis with either domain alone (inattentive, hyperactive-impulsive, or combined presentations). The DSM-5 is more inclusive. ICD-11 has now aligned more closely with DSM-5 by also allowing predominantly inattentive presentations.

2. Epidemiology

2nd commonest psychiatric disorder of childhood (after anxiety disorders) ^[2]
Worldwide pooled prevalence: approximately 5–7% of children and adolescents (meta-analyses) ^[2]
Prevalence in Hong Kong: 2.2% (males) vs 0.7% (females) — note that this likely underestimates true prevalence due to cultural factors and referral patterns ^[2]
Adult ADHD prevalence: ~2.5–4% of adults globally — a substantial proportion do not "grow out of it"
Lower prevalence in low-income countries — likely reflects under-recognition rather than true absence ^[2]

Sex ratio: Males > Females, roughly 3:1 in children (clinic-referred samples); ~2:1 in community samples
- Why the sex difference? Boys more often present with the hyperactive-impulsive (externalising) type, which is more disruptive and therefore more likely to trigger referral. Girls more often present with the predominantly inattentive (internalising) type — the "quiet daydreamer" — which is under-recognised ^[2]
Age of onset: arises early in development (before school age): 55–65% by age 7, 93% by age 12, 98% by age 16 ^[2]
- DSM-5 requires symptoms present before age 12
- ICD-10 requires symptoms present before age 6

This is a critical exam topic. ADHD rarely travels alone.

Comorbidities are very common (~50% of ADHD cases), especially in severe cases (↑ comorbidities with ↑ number of ADHD symptoms) ^[2]

Comorbidity	Approximate Frequency	Key Relationship
ODD (Oppositional Defiant Disorder)	~40%	Most common comorbidity; shares externalising trait liability ^[2]
Conduct Disorder (CD)	~20%	When ADHD + CD co-occur, prognosis is particularly poor (antisocial trajectory, substance abuse, criminality) ^[2]
Learning Disorders	~25%	Specific reading/maths disabilities; separate from ADHD but share genetic risk ^[2]
Tic Disorders	~5%	Tourette syndrome overlaps; both involve basal ganglia dysfunction ^[2]
Mood Disorders (depression, dysthymia)	~20%	Chronic failure and criticism → demoralisation; also shared genetic vulnerability ^[2]
Anxiety Disorders	~25%	Can mimic inattention (distracted by worries rather than external stimuli) ^[2]
Substance Abuse (SA)	~15%	Impulsivity → risk-taking; self-medication hypothesis ^[2]
ASD	Variable (~20–50% bidirectional)	Both are neurodevelopmental; share genetic overlap; DSM-5 now allows dual diagnosis

Overlap Table — Know This for Exams

Many ADHD symptoms overlap with other conditions. The key differentiating feature is pervasiveness and developmental onset:

Feature	ADHD	ODD/CD	GAD	Depression	Mania
Restlessness	✓		✓
Poor concentration	✓		✓	✓	✓
↑ Motor activity	✓				✓
Distractibility	✓		✓		✓
Irritability		✓	✓	✓	✓

^[2]

3. Risk Factors

Think of ADHD risk factors in a biopsychosocial framework, but the biological factors dominate:

Heritability is ~70–80% — comparable to schizophrenia and bipolar affective disorder. This is one of the most heritable psychiatric conditions ^[2]
- Family studies: ~1/4 of siblings of an ADHD proband also have ADHD ^[2]
- Twin studies: MZ > DZ concordance rates (MZ concordance ~70–80%, DZ ~30–40%) ^[2]
- Implicated genes: common and rare variants affecting dopamine and serotonin (5-HT) systems ^[2]
  - Specific candidate genes: DRD4 (dopamine receptor D4 — the 7-repeat allele), DRD5, DAT1/SLC6A3 (dopamine transporter gene), 5-HTT/SLC6A4 (serotonin transporter), SNAP-25 (synaptosomal-associated protein — involved in neurotransmitter release)
  - GWAS studies have identified polygenic architecture — many common variants of small effect rather than a single "ADHD gene"

Clinical signs suggestive of neurodevelopmental impairment/delay: clumsiness, language delay, abnormalities of speech → may result from early developmental insults ^[2]
Structural imaging: ↓ volume/cortical thickness, especially in grey matter of the basal ganglia ^[2]
- Specifically: reduced volume in the caudate nucleus, putamen, globus pallidus and prefrontal cortex (PFC)
- Cortical maturation delay: the PFC reaches peak cortical thickness ~3 years later in ADHD children vs. controls — the brain is not structurally abnormal, it is developmentally delayed
Functional studies: implicated fronto-striatal circuit, cerebellar abnormalities, white matter (WM) disruption and disordered connectivity ^[2]
- The fronto-striatal circuit (PFC → striatum → thalamus → back to PFC) is the brain's "executive control loop" — it governs planning, inhibition, working memory, and attentional set-shifting
- Cerebellar involvement explains the motor coordination difficulties (clumsiness)
Neurochemistry: hypoactivity of dopamine and noradrenaline in fronto-subcortical circuits → DRI/NRI often useful in ameliorating symptoms ^[2]
- Why dopamine? Dopamine in the PFC modulates "signal-to-noise ratio" of neural signalling — it tells the brain what is important to focus on and what to ignore. Low dopamine = poor signal-to-noise = everything gets equal attention = distractibility
- Why noradrenaline? Noradrenaline (norepinephrine) in the PFC supports sustained attention and arousal. Low noradrenaline = poor sustained attention = "zones out"
- This explains why stimulants (which increase dopamine and noradrenaline) paradoxically calm down ADHD patients — they are boosting the underactive "braking" circuits

The Dopamine Hypothesis of ADHD — Key Concept

The core neurochemical model: hypo-dopaminergic and hypo-noradrenergic states in the prefrontal cortex lead to deficient executive control (inhibition, working memory, attention). This is an inverted-U relationship — too little OR too much catecholamine activity in the PFC impairs function. Stimulant medications work by shifting patients from the "too low" side to the optimal zone.

Cognitive theories: ADHD is generally conceptualised as originating from deficits in executive functions ^[2]
- Barkley's model (1997): The core deficit is in behavioural inhibition — the inability to delay a prepotent response. This cascades into impairments in:
  - Working memory (can't hold information "online")
  - Self-regulation of affect/motivation/arousal
  - Internalisation of speech (the "inner voice" that guides behaviour)
  - Reconstitution (analysis and synthesis of behaviour — i.e., planning, problem-solving)
- Sonuga-Barke's dual-pathway model: Proposes two distinct pathways:
  1. Executive dysfunction pathway (fronto-striatal): leads to cognitive deficits → inattention
  2. Motivational pathway (ventral striatal/reward circuit): leads to delay aversion — ADHD children prefer immediate small rewards over larger delayed rewards → hyperactivity/impulsivity as an attempt to shorten subjective experience of delay

Perinatal factors ^[2]:
- Maternal alcohol and substance abuse during pregnancy (fetal alcohol spectrum → executive dysfunction)
- Low birth weight and prematurity (associated with white matter injury and PFC underdevelopment)
- Maternal smoking during pregnancy (nicotine is a dopaminergic agent → prenatal exposure may alter dopamine receptor development)
- Obstetric complications (hypoxia, infections)
Environmental factors ^[2]:
- Early psychosocial adversities (e.g., children raised in extreme deprivation) — e.g., Romanian orphan studies showed high rates of ADHD-like symptoms in severely deprived children
- Nutritional deficiencies and exposure to environmental toxins — particularly lead exposure (lead disrupts dopaminergic neurotransmission) and iron/zinc deficiency (cofactors in catecholamine synthesis)
- Excessive screen time in early childhood (controversial, but may exacerbate attentional difficulties via reinforcement of rapid attention-switching)
- Food additives / artificial colourings — modest evidence for exacerbating symptoms in some children, but not considered a primary cause

Note on Causation

A common exam mistake: ADHD is NOT caused by "bad parenting." While adverse parenting can worsen symptoms and outcomes, the primary drivers are neurobiological and genetic. Conversely, excellent parenting and structured environments can significantly mitigate symptoms — this is the basis for behavioural interventions.

4. Anatomy and Neurobiological Basis

Understanding the anatomy helps everything else make sense — the clinical features, the pharmacology, and the comorbidities.

Brain Region	Normal Function	Dysfunction in ADHD
Prefrontal Cortex (PFC) — especially dorsolateral PFC (dlPFC) and ventromedial PFC (vmPFC)	Executive functions: planning, working memory, sustained attention, inhibition, decision-making	↓ Activation → poor inhibition, distractibility, poor planning, impulsive decision-making
Basal Ganglia (caudate, putamen, globus pallidus)	Motor programme selection; gating of actions through the thalamus; reward processing	↓ Volume ^[2]; impaired action selection → motor restlessness, inability to suppress inappropriate actions
Anterior Cingulate Cortex (ACC)	Error monitoring, conflict detection, motivation	↓ Activity → failure to detect errors (careless mistakes), poor motivation for effortful tasks
Cerebellum	Motor coordination, timing, procedural learning	Cerebellar abnormalities ^[2] → clumsiness, poor timing, difficulty with sequencing
Corpus Callosum	Inter-hemispheric communication	Reduced size in some ADHD studies → disordered connectivity

Fronto-striatal (executive) circuit: PFC → caudate/putamen → globus pallidus → thalamus → PFC
- Governs: cognitive control, inhibition, working memory
- Neurotransmitter: Dopamine (D1 receptors in PFC for "stay on task"; D2 in striatum for action selection)
Fronto-cerebellar circuit: PFC → pons → cerebellum → thalamus → PFC
- Governs: motor timing, procedural learning
- Dysfunction → clumsiness, difficulty with time perception
Mesolimbic (reward) circuit: VTA → nucleus accumbens → PFC
- Governs: motivation, reward anticipation, delay tolerance
- Dysfunction → delay aversion, preference for immediate reward, poor sustained motivation

Neurotransmitter	Role in ADHD	Therapeutic Implication
Dopamine (DA)	Hypoactive in PFC and striatum → poor signal-to-noise, impaired inhibition, reward deficiency	Stimulants (methylphenidate, amphetamines) → block dopamine reuptake transporter (DAT) → ↑ synaptic DA
Noradrenaline (NA)	Hypoactive in PFC → poor sustained attention and arousal	Stimulants also ↑ NA; atomoxetine (selective NRI) specifically targets this pathway
Serotonin (5-HT)	Modulates impulsivity and emotional regulation	Less directly targeted; some genetic variants in 5-HT system implicated ^[2]

5. Classification

DSM-5 uses the term "presentation" rather than "subtype" because the presentation can change over a patient's lifetime (e.g., a child with combined type may present as predominantly inattentive in adulthood as hyperactivity diminishes):

Presentation	Criteria	Typical Profile
Predominantly Inattentive	≥ 6/9 inattention criteria (≥ 5 if age ≥ 17)	"The daydreamer" — quiet, disorganised, forgetful; more common in girls; often diagnosed later
Predominantly Hyperactive-Impulsive	≥ 6/9 hyperactivity-impulsivity criteria (≥ 5 if age ≥ 17)	"The whirlwind" — constantly moving, can't wait; more common in young children (pre-school)
Combined	Meets criteria for both	Most common presentation overall; most likely to be referred

F90.0 Disturbance of activity and attention (= ADHD combined type, without conduct disorder)
F90.1 Hyperkinetic conduct disorder (= ADHD + comorbid conduct disorder — a distinctly poor-prognosis group)
F90.8 Other hyperkinetic disorders
F90.9 Hyperkinetic disorder, unspecified

Note: ICD-10 requires both inattention and hyperactivity → it is a narrower definition than DSM-5 and essentially only captures the "combined" and "hyperactive" presentations. ICD-10 does not formally recognise a "predominantly inattentive" subtype under F90.

ICD-11 (now in use) has aligned with DSM-5 by recognising:

Predominantly inattentive presentation
Predominantly hyperactive-impulsive presentation
Combined presentation
This is a significant update for clinical practice in jurisdictions using ICD.

Mild: Few symptoms beyond minimum criteria; minor functional impairment
Moderate: Between mild and severe
Severe: Many symptoms beyond minimum criteria OR marked impairment in multiple domains (social, academic, occupational)

6. Clinical Features

The cardinal features of ADHD can be organised into three domains: inattention, hyperactivity, and impulsivity. These must be:

Pervasive (across situations) — not just at school or just at home ^[2]
Early onset (< 6y in ICD-10, < 12y in DSM-5) ^[2]
Developmentally inappropriate — beyond what is expected for the child's age and IQ
Causing functional impairment in ≥ 2 settings

Inattention presents later in school-age; best assessed at P1 (Primary 1) — because this is when sustained attention demands increase significantly and the deficit becomes apparent ^[2]

Symptom	Description	Pathophysiological Basis
Poor persistence towards goals and tasks	Cannot sustain attention on homework, chores, conversations; "zones out" mid-task	Hypoactive PFC (dlPFC) → impaired sustained attention and working memory; the dopamine "signal" that says "this task is important, keep going" is too weak
↓ Attention to details, careless mistakes	Makes errors in schoolwork that seem avoidable; skips steps	Impaired anterior cingulate cortex (ACC) error-monitoring; inadequate dopamine in PFC → poor top-down attentional control → misses fine details
Difficulty listening when spoken to directly	Appears "not to hear" even when there is no auditory problem	Not an auditory deficit — it is a filtering deficit: low DA in PFC means the brain cannot prioritise the speaker's voice over background stimuli
Fails to follow through on instructions	Starts tasks but doesn't finish; loses track of multi-step instructions	Impaired working memory (a PFC-mediated executive function); cannot hold the instruction sequence "online"
Difficulty organising tasks and activities	Messy desk, chaotic schedule, poor time management	PFC-mediated planning and sequencing deficit
Avoids tasks requiring sustained mental effort	Refuses or procrastinates on homework, reading, paperwork	Delay aversion (mesolimbic pathway) — effortful tasks with delayed reward are aversive; also genuine cognitive fatigue from compensatory effort
Loses things necessary for tasks	Loses pencils, books, phone, keys	Poor prospective memory (remembering to remember) — PFC dysfunction
Easily distracted by extraneous stimuli	Head turns at every noise; mind wanders during lessons	Impaired selective attention / attentional gating — the PFC normally suppresses irrelevant sensory input; low catecholamines → failure of this gating → all stimuli compete equally
Forgetful in daily activities	Forgets appointments, chores, bringing items to school	Impaired working memory and prospective memory (PFC-dependent)

Hyperactivity usually presents earlier than inattention → due to executive inhibition deficits ^[1]^[2]

Symptom	Description	Pathophysiological Basis
Fidgets with or taps hands/feet, squirms in seat	Constant small movements; cannot sit still	Impaired motor inhibition via fronto-striatal circuit; the basal ganglia cannot adequately suppress unwanted motor programmes → excess motor output
Leaves seat when remaining seated is expected	Gets up in class, meetings, cinema	Same motor inhibition deficit; also may represent stimulation-seeking — moving provides sensory input that partially compensates for hypo-aroused PFC
Runs about or climbs in inappropriate situations	In younger children: climbing furniture, running in corridors; in adolescents/adults: subjective feelings of restlessness	Excessive motor drive due to disinhibited motor circuits; in adults, the overt motor behaviour diminishes but the internal restlessness persists
Unable to play or engage in leisure activities quietly	Loud play, constant commentary	Impaired regulation of motor output and arousal; low PFC inhibitory tone → cannot modulate activity level to context
"On the go" or "driven by a motor"	Relentless activity from morning to night; exhausting for parents and teachers	Reflects chronically hypo-aroused PFC — the child is unconsciously trying to increase arousal through constant movement (a compensatory mechanism)
Talks excessively	Unceasing chatter; cannot stop talking even when told to	Impaired verbal inhibition (a PFC executive function); also related to impulsivity — the "brakes" on speech output are weak

Symptom	Description	Pathophysiological Basis
Blurts out answers before questions are completed	Shouts out in class; finishes other people's sentences	Impaired response inhibition (the ability to withhold a prepotent response) — this is the core executive deficit in Barkley's model; fronto-striatal "braking" failure
Difficulty waiting their turn	Cannot queue; wants everything "now"	Delay aversion (mesolimbic reward pathway dysfunction) — waiting is experienced as intensely unpleasant because the brain cannot tolerate the absence of immediate reward
Interrupts or intrudes on others	Butts into conversations and games; uses others' things without permission	Impaired social inhibition — the PFC normally applies "social brakes" to prevent inappropriate behaviour; low catecholamines → these brakes are weak

Beyond the core triad, there are important associated features:

Feature	Explanation
Disinhibition in social relationships	Acts overly familiar with strangers; no sense of social distance — reflects PFC-mediated social cognition impairment ^[2]
Recklessness in dangerous situations	Crosses roads without looking; climbs to dangerous heights — impaired risk assessment (vmPFC dysfunction) ^[2]
Impulsive flouting of social rules	Breaking rules not out of defiance (cf. ODD) but out of failure to inhibit the impulse ^[2]
Motor clumsiness	Clumsiness, language delay, abnormalities of speech — neurodevelopmental soft signs reflecting cerebellar and motor cortex immaturity ^[2]
Learning disorders	Occur with undue frequency and should be noted separately ^[2]; often co-exist because of shared frontal dysfunction, but are distinct diagnoses
Emotional dysregulation	Low frustration tolerance, anger outbursts, mood lability — increasingly recognised as a core feature rather than just a comorbidity; reflects impaired PFC regulation of limbic system
Sleep difficulties	Difficulty settling at night (the "revving brain"), delayed sleep onset; affects ~25–50% of ADHD children
Low self-esteem	Secondary to chronic academic failure, social rejection, and frequent criticism from adults

6.5 Clinical Features by Developmental Stage

Understanding how ADHD manifests across the lifespan is crucial:

Predominant presentation: hyperactivity and impulsivity (inattention is difficult to assess at this age because of wide normal variation)
Features: constant running, climbing, inability to sit for stories; frequently "into everything"; accident-prone
Only extreme levels should lead to a diagnosis in preschool children ^[2] — the normal range of activity is very wide at this age

All three domains become apparent: inattention becomes prominent as academic demands increase
Best assessed at P1 (Primary 1) — it usually takes a few weeks for new P1 students to learn to comply with classroom rules ^[2]
Functional impact: academic underachievement, peer rejection (due to intrusiveness), teacher frustration, parental stress
Childhood functional impairment: school failure, injuries ^[2]

Hyperactivity tends to diminish (becomes more of an internal restlessness)
Inattention and impulsivity persist and cause increasing problems as academic demands rise
Risk-taking behaviours emerge (substance experimentation, reckless driving, unprotected sex)
Comorbid mood/anxiety disorders and oppositional behaviours often intensify

~50% retain full diagnostic criteria in adolescence; ~40–60% experience problems in adulthood ^[2]

The presentation of ADHD changes qualitatively in adulthood ^[2]:

Domain	Childhood Manifestation	Adult Manifestation
Inattention	Difficulty sustaining attention; doesn't listen; no follow-through; cannot organise; loses important items; easily distractible; forgetful	Difficulty sustaining attention in meetings, reading or paperwork; paralyzing procrastination; slowness, inefficiency; poor time management; disorganisation ^[2]
Hyperactivity	Squirms and fidgets; can't stay seated; runs/climbs excessively; can't play/work quietly; "on the go"; talks excessively	Workaholic; overscheduled and overwhelmed; self-select very active jobs; constant activity leading to family tension; talks excessively ^[2]
Impulsivity	Blurts out answers; can't wait turns; intrudes or interrupts others	Mainly as low frustration tolerance; losing temper; quitting jobs; ending relationships; driving too fast; addictive personality ^[2]

"When deadlines cannot be met, they often then choose to procrastinate indefinitely instead of embarking on work." ^[2]

Adult ADHD — Don't Miss This

Adult ADHD is commonly missed because:

Hyperactivity is less overt — adults fidget internally rather than running around
Adults develop compensatory strategies that partially mask symptoms
Clinicians may attribute symptoms to depression, anxiety, or personality traits
The patient may not recall childhood symptoms (collateral history from parents is essential)

Diagnosis of hyperkinetic disorder can still be made in adult life. The grounds are the same, but attention and activity must be judged with reference to developmentally appropriate norms. ^[2]

Course: generally shows age-dependent ↓ severity (hyperactivity > impulsiveness > inattention) — hyperactivity is the first to improve, impulsivity partially improves, inattention is the most persistent ^[2]
~50% retain full diagnostic criteria in adolescence ^[2]
~40–60% experience problems in adulthood ^[2]
Poor prognostic factors: learning difficulties, antisocial behaviour, severe overactivity ^[2]
In particular, when comorbid with CD, patients are at risk of antisocial behaviour, criminal behaviours, and substance abuse ^[2]

When hyperkinesis was present in childhood but has disappeared and been succeeded by another condition, such as dissocial personality disorder or substance abuse, the current condition rather than the earlier one is coded. ^[2]

Life Domain	Impact
Academic	Underachievement relative to IQ; grade retention; school dropout
Social	Peer rejection (intrusiveness, turn-taking difficulty); difficulty maintaining friendships
Family	Parental stress; sibling conflict; marital strain from managing the child
Safety	Injuries/accidents from impulsivity and risk-taking ^[2]
Occupational (adults)	Occupational failure, self-esteem issues, relationship problems, substance abuse, injuries/accidents ^[2]
Legal	Higher rates of traffic violations, arrests (especially when comorbid with CD)
Emotional	Low self-esteem, demoralisation, secondary depression

High Yield Summary

Definition: ADHD is a neurodevelopmental disorder of inattention ± hyperactivity-impulsivity, pervasive across settings, with early onset (< 12y DSM-5, < 6y ICD-10), causing functional impairment.
Epidemiology: 2nd commonest childhood psychiatric disorder; M > F (3:1); prevalence ~5–7% in children; ~50% comorbid with other disorders (ODD ~40%, CD ~20%, learning disorders ~25%, anxiety ~25%, mood ~20%).
Pathophysiology: Hypoactive dopamine and noradrenaline in fronto-striatal and mesolimbic circuits → executive dysfunction (poor inhibition, working memory, attention) + delay aversion.
Genetics: Heritability ~70–80%; polygenic; involves dopamine and serotonin system genes.
Neuroimaging: ↓ Volume in basal ganglia and PFC; delayed cortical maturation; disrupted fronto-striatal connectivity.
Three symptom domains: Inattention (presents later, most persistent), Hyperactivity (presents first, improves most with age), Impulsivity (intermediate trajectory).
Lifespan: Hyperactivity > impulsivity > inattention in age-dependent improvement; ~50% retain criteria in adolescence; ~40–60% have adult functional impairment.
ICD-10 vs DSM-5: ICD-10 (Hyperkinetic Disorder, F90) requires BOTH inattention + hyperactivity; DSM-5 allows EITHER domain; ICD-11 has aligned with DSM-5.
Key comorbidity to remember: ADHD + CD = worst prognosis (antisocial trajectory, substance abuse, criminality).
Adult ADHD: Presents differently — internalised restlessness, procrastination, poor time management, relationship instability, low frustration tolerance.

Active Recall - ADHD Definition, Epidemiology, Aetiology & Clinical Features

^[1] Senior notes: ryanho-psych.md (Section 12.3 - summary table of childhood psychiatric disorders) ^[2] Senior notes: ryanho-psych.md (Section 12.3 - Attention-deficit Hyperactivity Disorder)

Differential Diagnosis of ADHD

Getting the differential diagnosis right in ADHD is absolutely crucial — and it's one of the trickiest areas in child psychiatry. Why? Because many diagnostic criteria of ADHD overlap with other comorbidities ^[2]. Inattention, restlessness, distractibility, and impulsivity are non-specific symptoms that appear across a wide range of psychiatric, neurodevelopmental, and medical conditions. Your job on the ward (and in the exam) is to parse out what is driving the symptom.

The golden rules for differentiating ADHD from its mimics:

Pervasiveness: ADHD symptoms occur across all settings (home, school, social). If symptoms only appear in one context, think of something else.
Developmental onset: ADHD is early onset (before age 12 in DSM-5, before age 6 in ICD-10). If a previously well child suddenly develops "ADHD-like" symptoms at age 14, think mood disorder, substance use, or trauma.
Course: ADHD is chronic and trait-like — present every day since early childhood. If symptoms are episodic, think bipolar, depression, or substance use.
Context of the inattention: Is the child distracted by external stimuli and novel activities (→ ADHD) or by internal worries (→ anxiety) or by low mood and anhedonia (→ depression)?

Differential Diagnosis	Overlapping Features with ADHD	Salient Differentiating Features	Why the Confusion Exists (First Principles)
Oppositional Defiant Disorder (ODD)	Resists schoolwork/tasks; disruptive behaviour; doesn't follow instructions	ODD patients resist work because they resist conforming to others' demands — characterised by negativity, hostility and defiance. This must be differentiated from aversion due to difficulty sustaining mental effort, forgetting instructions and impulsivity. ODD can occur together with ADHD. ^[2]	Both involve non-compliance, but the mechanism differs: ADHD = "can't do it" (executive dysfunction); ODD = "won't do it" (defiance). In ADHD, the child is often remorseful afterwards; in ODD, there is deliberate hostility. Remember they co-occur in ~40% of cases.
Conduct Disorder (CD)	Rule-breaking, impulsive aggression, risk-taking behaviour	CD involves premeditated aggression, cruelty, destruction of property, theft, violation of others' rights. ADHD aggression is impulsive and unplanned. CD has callous-unemotional traits.	ADHD impulsivity leads to accidental rule-breaking; CD involves intentional antisocial behaviour. When comorbid (ADHD + CD), the prognosis is particularly poor ^[2].
Learning Disorder / Intellectual Disability (ID) / Gifted Child	Appears inattentive in class; avoids schoolwork; poor academic performance	These individuals may appear inattentive because of frustration, lack of interest or limited ability. However, this inattention is not typically seen outside of school work (i.e., not pervasive). Children placed in settings inappropriate for their levels may appear bored and show typical symptoms of ADHD. Again, symptoms are not evident during non-academic tasks. ^[2]	A child with a reading disorder struggles to attend to text → looks "inattentive." A gifted child is bored in a normal classroom → looks "restless." The key: are the symptoms pervasive? In these cases, symptoms disappear in appropriately stimulating or ability-matched environments.
Autism Spectrum Disorder (ASD)	Inattention, social dysfunction, difficult behaviour; ADHD may also have impaired social function (due to e.g., inability to focus) ^[2]	In ADHD, social difficulties arise from impulsivity and poor self-control rather than the poor social skills and restricted interests seen in ASD. ADHD has normal pragmatic language skills, nonverbal social behaviour and imaginary play. ^[2]	Both are neurodevelopmental and share genetic overlap. DSM-5 now allows dual diagnosis (ADHD + ASD). The distinguishing question: does the child want to socialise but fail due to impulsivity (ADHD), or does the child have fundamental difficulty understanding social reciprocity (ASD)?
Anxiety Disorders (GAD, separation anxiety)	Poor concentration, restlessness, distractibility, difficulty completing tasks	ADHD is often accompanied by anxiety. One should distinguish the cues of their distraction — whether they are related to worrying themes (anxiety) or to external stimuli, new activities, preoccupation with enjoyable activities (ADHD). ^[2]	Anxious children look inattentive because their working memory is consumed by worry (internal stimuli), not because of PFC hypofunction. In ADHD, distraction is by the external world. Anxiety also causes somatic symptoms (stomachaches, headaches) and avoidance that ADHD alone does not. Co-occurrence is ~25%.
Depressive Disorder (MDD, Dysthymia)	Poor concentration, poor motivation, indecisiveness, psychomotor changes, irritability	Both are associated with diminished ability to think/concentrate, poor motivation towards daily activities and indecisiveness. However, depression usually has later onset and episodic course, and these symptoms usually only become prominent during depressive episodes when mood is low. ^[2]	Depression impairs concentration via anhedonia (nothing seems worth attending to) and psychomotor retardation (slowed processing). ADHD impairs concentration via hypo-dopaminergic PFC. The timeline is key: ADHD = lifelong since early childhood; depression = onset typically after puberty and episodic.
Bipolar Affective Disorder (BAD) — Mania	Distractibility, impulsivity, talkativeness, ↑ motor activity, ↑ energy ^[2]^[3]	ADHD and mania are both associated with distractibility, impulsivity and talkativeness. In BAD, these features tend to occur episodically and may be associated with elated mood and grandiosity. ^[2] ADHD should not have ↑ self-esteem, grandiosity, flight of ideas, ↓ need for sleep etc. Course: usually more chronic (trait-like) than episodic. ^[3]	This is a classic exam question. Both conditions activate similar circuits (fronto-striatal, mesolimbic). The critical differences: (1) Episodicity — mania is episodic with clear onset/offset, ADHD is chronic/trait-like; (2) Grandiosity and elation — present in mania, absent in ADHD; (3) Sleep — manic patients have genuinely ↓ need for sleep (feel refreshed after 2–3 hours), while ADHD patients want to sleep but can't settle; (4) Age of onset — BAD onset usually in late adolescence/young adulthood.
Substance Abuse (SA) Disorders	ADHD-like symptoms: inattention, impulsivity, restlessness, poor judgement	ADHD-like symptoms can occur with substance use, but these are episodic and occur only in the context of substance use. ^[2]	Substances (stimulants in intoxication; cannabis, alcohol in withdrawal) disrupt PFC function → ADHD-like picture. The key: temporal relationship to substance use. Also, ADHD predisposes to SA (~15% comorbidity), so both may coexist — the chronological history and collateral from parents about childhood behaviour is essential.
Post-Traumatic Stress Disorder (PTSD) / Trauma	Hypervigilance (→ looks like hyperactivity), poor concentration, irritability, sleep disturbance	PTSD has identifiable traumatic event(s), re-experiencing symptoms (flashbacks, nightmares), avoidance of trauma reminders, and emotional numbing. ADHD does not have these.	Trauma-exposed children can appear "hyperactive" due to hyperarousal (noradrenergic overdrive) and "inattentive" because of dissociation or intrusive trauma memories consuming working memory. Always screen for trauma/ACEs in an ADHD assessment.
Thyroid Disorders (Hyperthyroidism)	Restlessness, poor concentration, irritability, ↑ motor activity	Thyroid dysfunction has systemic signs: tachycardia, tremor, weight loss/gain, heat/cold intolerance, goitre. Thyroid function tests (TFTs) are diagnostic.	Hyperthyroidism increases overall sympathetic tone → agitation, restlessness. This is a medical mimic that must be excluded, especially in new-onset "ADHD-like" presentations.
Sleep Disorders (OSA, restless legs, insufficient sleep)	Daytime inattention, hyperactivity (paradoxically in children), irritability, poor academic performance	Sleep history reveals snoring, restless sleep, excessive daytime sleepiness. Polysomnography if indicated. Symptoms improve when sleep is normalised.	Sleep-deprived children paradoxically become hyperactive rather than sleepy (unlike adults). This is because the immature PFC is exquisitely sensitive to sleep deprivation → disinhibition → motor restlessness. Always take a sleep history.
Sensory Impairment (hearing/vision)	Appears not to listen, inattentive in class, poor academic performance	Audiometry and visual testing are normal in ADHD. Sensory impairment is not pervasive across all settings once accommodated.	A child who can't hear the teacher looks "inattentive." A child who can't see the board looks "disengaged." Simple screening resolves this.
Personality Disorders (esp. Borderline PD) — in adults/adolescents	Impulsivity, temper, mood lability; features similar to hypomania ^[3]	Personality disorders tend to involve more stable and enduring behaviour pattern (cf. episodic in mania). No FHx of BAD. Rapid shifts of mood (over hours and days). No classic symptoms of mania (↑ energy, grandiosity). Mood disturbances often triggered by interpersonal issues. ^[3]	In adults, BPD and adult ADHD both present with impulsivity, emotional dysregulation, and unstable relationships. BPD impulsivity is typically interpersonally triggered (abandonment fears), whereas ADHD impulsivity is contextually non-specific (occurs in all situations). They can co-occur.
Normal developmental variation	Active, energetic child; short attention span in young children	Wide normal variation in activity and attention, especially in preschoolers. Only diagnose if excessive for age and IQ and causing functional impairment.	Active ≠ ADHD. Some children are simply temperamentally active. The diagnosis requires functional impairment and symptoms that are clearly beyond developmental norms.

This table from the notes is high-yield for exams — it shows which features overlap across conditions ^[2]:

Feature	ADHD	ODD/CD	GAD	Depression	Mania
Restlessness	✓		✓
Poor concentration	✓		✓	✓	✓
↑ Motor activity	✓				✓
Distractibility	✓		✓		✓
Irritability		✓	✓	✓	✓

Notice: Irritability is NOT a core ADHD feature — it's a feature of ODD/CD, anxiety, depression, and mania. If prominent irritability dominates, consider these alternatives (or comorbidities) ^[2].

ADHD vs Mania — The Classic Exam Trap

This is one of the most commonly tested differentials, especially when the lecture slides list Attention deficit and hyperactivity disorder as a differential of manic episodes ^[3]. Both share distractibility, impulsivity, talkativeness, and increased activity. Remember:

Episodicity: Mania = episodes with clear onset/offset; ADHD = chronic trait since childhood
Grandiosity / ↑ self-esteem: Present in mania, absent in ADHD (ADHD patients typically have low self-esteem)
Flight of ideas: In mania, thoughts race with loose associations and goal-directed shifts; in ADHD, thoughts are scattered but do not have the pressured, driven quality
↓ Need for sleep: In mania, patients feel genuinely refreshed after minimal sleep; in ADHD, patients have difficulty initiating sleep but still need normal amounts
ADHD should not have ↑ self-esteem, grandiosity, flight of ideas, ↓ need for sleep etc. ^[3]
Course: usually more chronic (trait-like) than episodic ^[3]

ADHD vs Anxiety — The Subtle Mimic

Both produce poor concentration and restlessness. The distinguishing question is: what is the child distracted by?

ADHD: Distracted by the external world — a bird outside the window, a classmate's pencil, a noise in the corridor. The child is stimulus-driven.
Anxiety: Distracted by the internal world — worries about performance, health, family, catastrophic thoughts. The child may appear "spaced out" because their working memory is consumed by worry.

One should distinguish the cues of their distraction, whether they are related to worrying themes (anxiety) or to external stimuli, new activities, preoccupation with enjoyable activities (ADHD). ^[2]

ADHD vs ASD — Social Difficulties with Different Mechanisms

Both present with social difficulties, but the mechanism is fundamentally different:

ADHD: The child wants to socialise and understands social rules but fails to execute them because of impulsivity (e.g., interrupts, talks over others, can't take turns). Impairment is usually milder. Normal pragmatic language skills, nonverbal social behaviour and imaginary play. ^[2]
ASD: The child has a fundamental deficit in social reciprocity — struggles to read facial expressions, understand sarcasm, engage in back-and-forth conversation, or develop age-appropriate friendships. Restricted interests and repetitive behaviours are present.

DSM-5 allows both diagnoses to co-occur (previously, ASD was an exclusion criterion for ADHD).

ADHD vs Learning Disorder / ID / Gifted Mismatch

This inattention is not typically seen outside of school work (i.e., not pervasive). ^[2]

A child with undiagnosed dyslexia looks inattentive during reading — but is perfectly attentive during sports, art, or video games. A gifted child is unstimulated in a normal classroom and appears restless — but is deeply engaged when intellectually challenged. The litmus test: does the problem persist across all settings and activities? If not, it's not ADHD.

When you see a child referred for possible ADHD, your differential diagnosis workup should systematically consider:

Assessment Area	Purpose	What You're Ruling Out
Detailed developmental history (from parents)	Confirm early onset, pervasiveness, developmental trajectory	Late-onset mimics (depression, BAD, PTSD, substance use)
Behaviour across settings (home, school, social — use rating scales from both parents and teachers)	Confirm pervasiveness	Situation-specific causes (learning disorder, classroom mismatch)
Mood screen	Assess for low mood, anhedonia, elation, irritability, episodicity	Depression, BAD, dysthymia
Anxiety screen	Assess for excessive worry, avoidance, somatic complaints	GAD, separation anxiety, social anxiety
Trauma screen	Assess for ACEs, abuse, neglect, witnessed violence	PTSD, reactive attachment disorder
Substance use history (in adolescents)	Temporal relationship between substance use and symptoms	Substance-induced ADHD-like symptoms
Sleep history	Snoring, sleep duration, sleep onset latency, restless legs	OSA, insufficient sleep, circadian rhythm disorder
Medical history + physical examination	Thyroid signs, neurological signs, hearing/vision	Hyperthyroidism, seizures, sensory impairment, lead exposure
Psychometric/cognitive testing	IQ testing, academic achievement testing	Intellectual disability, specific learning disorders, giftedness
Assessment for ASD	Social reciprocity, restricted interests, repetitive behaviours	ASD (which can co-occur)

High Yield Summary

ADHD symptoms are non-specific — inattention, hyperactivity, and impulsivity appear in many conditions. Always consider the differential systematically.
The 3 golden rules for ADHD diagnosis over mimics: (a) Pervasive across ≥ 2 settings, (b) Early onset (before age 12), (c) Chronic/trait-like (not episodic).
ADHD vs ODD: "Can't do it" (executive dysfunction) vs "Won't do it" (defiance). Co-occur in ~40%.
ADHD vs Anxiety: Distracted by external stimuli (ADHD) vs internal worries (anxiety).
ADHD vs Depression: Lifelong since childhood (ADHD) vs later onset and episodic (depression). Both impair concentration but via different mechanisms.
ADHD vs Mania: Chronic trait-like course (ADHD) vs episodic with elated mood, grandiosity, ↓ need for sleep, flight of ideas (mania). ADHD should NOT have grandiosity or ↓ need for sleep.
ADHD vs ASD: Wants to socialise but fails due to impulsivity (ADHD) vs fundamental deficit in social reciprocity (ASD). Can co-occur.
ADHD vs Learning Disorder/ID/Gifted: Symptoms only during academic tasks (learning disorder) vs pervasive (ADHD).
ADHD vs Substance Abuse: Symptoms only in context of substance use (SA) vs lifelong (ADHD). Both can co-exist.
Always exclude medical causes: Thyroid, sleep disorders, sensory impairment, seizures, lead exposure.

Active Recall - ADHD Differential Diagnosis

References

^[1] Senior notes: ryanho-psych.md (Section 12.3 — summary table of childhood psychiatric disorders) ^[2] Senior notes: ryanho-psych.md (Section 12.3 — Attention-deficit Hyperactivity Disorder, including D/dx table and clinical features) ^[3] Senior notes: ryanho-psych.md (Section 7.1.2 — Approach to Elated or Irritable Mood; and Bipolar Disorder differential diagnosis of ADHD); Lecture slides: GC 163. I am a superman Bipolar disorder.pdf (p10 — Differential diagnosis of manic episode)

Diagnostic Criteria

ADHD is a clinical diagnosis — there is no blood test, no brain scan, no single questionnaire that "confirms" it. The diagnosis rests on a careful clinical assessment demonstrating that the patient meets standardised criteria. Let me walk you through both the DSM-5 and ICD-10/ICD-11 criteria, explain the reasoning behind each criterion, and then detail the full assessment algorithm and investigation modalities.

From first principles: ADHD reflects a dimensional trait (executive function capacity) that exists on a spectrum in the population — like blood pressure or height. There is no qualitative "switch" that flips at a certain biomarker level. Instead, we define a threshold above which the trait causes clinically significant functional impairment. The diagnostic criteria operationalise this threshold. Neuroimaging and neuropsychological testing can support the diagnosis but are neither sufficiently sensitive nor specific to serve as standalone diagnostic tools.

DSM-5 Diagnostic Criteria (Attention-Deficit/Hyperactivity Disorder)

The DSM-5 criteria are the most widely used globally and are the standard for clinical practice and research. I'll present each criterion and explain why it exists ^[2].

Criterion A — Symptom Domains

A persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development, with ≥ 6 of the following criteria persisting for ≥ 6 months to a degree that is inconsistent with developmental level and that directly negatively impacts social and academic/occupational activities. (≥ 5 criteria if age ≥ 17y) ^[2]

Why ≥ 6 months? — To ensure the symptoms are persistent and not transient reactions to stressors (e.g., a child who is temporarily inattentive after parental divorce). Six months is long enough to distinguish a trait from a state.

Why "inconsistent with developmental level"? — A 3-year-old who can't sit still for 30 minutes is normal. A 10-year-old who can't sit still for 5 minutes is not. The same behaviour has different diagnostic significance depending on age.

Why ≥ 5 (instead of ≥ 6) for ages ≥ 17? — Adults have developed compensatory strategies and the expression of symptoms evolves. A lower threshold acknowledges that fewer overt symptoms may still cause significant impairment in the more demanding adult environment.

Item	Criterion	Cognitive Basis
(a)	Often fails to give close attention to details or makes careless mistakes in schoolwork, at work, or during other activities ^[2]	Impaired selective attention and ACC error-monitoring → details are missed because the brain's "quality control" system is underactive
(b)	Often has difficulty sustaining attention in tasks or play activities ^[2]	Impaired sustained attention (dlPFC) → the dopamine signal that says "keep focusing here" fades too quickly
(c)	Often does not seem to listen when spoken to directly ^[2]	Impaired attentional gating → the speaker's voice is not prioritised over competing sensory input; the child is not ignoring deliberately
(d)	Often does not follow through on instructions and fails to finish schoolwork, chores, or duties at workplace ^[2]	Impaired working memory → cannot hold multi-step instructions online long enough to execute them; also impaired goal-directed persistence
(e)	Often has difficulty organising tasks and activities ^[2]	Impaired executive planning (dlPFC) → cannot break complex tasks into manageable steps or sequence them logically
(f)	Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort ^[2]	Delay aversion (mesolimbic pathway) + genuine cognitive fatigue → effortful tasks with delayed reward are experienced as intensely aversive
(g)	Often loses things necessary for tasks or activities ^[2]	Impaired prospective memory (remembering to keep track of possessions) → PFC-dependent "reminder" function is weak
(h)	Is often easily distracted by extraneous stimuli ^[2]	Impaired inhibition of irrelevant sensory input → PFC cannot suppress bottom-up attentional capture; everything competes equally for attention
(i)	Is often forgetful in daily activities ^[2]	Impaired working memory and prospective memory → forgets appointments, routine tasks, items needed for the day

Item	Criterion	Cognitive Basis
(a)	Often fidgets with or taps hands or feet or squirms in seat ^[2]	Impaired motor inhibition (fronto-striatal circuit) → basal ganglia fail to suppress unwanted motor programmes; also compensatory stimulation-seeking to increase PFC arousal
(b)	Often leaves seat in situations when remaining seated is expected ^[2]	Same motor disinhibition; stronger drive to move overcomes the learned social rule of "stay seated"
(c)	Often runs about or climbs in situations where it is inappropriate ^[2]	Excessive motor drive; in adolescents/adults, may manifest as subjective restlessness rather than overt climbing
(d)	Often unable to play or engage in leisure activities quietly ^[2]	Impaired regulation of arousal level → cannot modulate activity to match the situation's demands
(e)	Is often "on the go," acting as if "driven by a motor" ^[2]	Chronically hypo-aroused PFC → constant movement is a compensatory mechanism to upregulate arousal
(f)	Often talks excessively ^[2]	Impaired verbal inhibition → the "brakes" on speech output are weak; words are produced faster than they can be filtered
(g)	Often blurts out an answer before a question has been completed ^[2]	Impaired response inhibition (the core deficit in Barkley's model) → the prepotent response cannot be suppressed
(h)	Often has difficulty waiting his or her turn ^[2]	Delay aversion → waiting is experienced as intensely unpleasant; impaired ability to tolerate the gap between desire and gratification
(i)	Often interrupts or intrudes on others ^[2]	Impaired social inhibition → PFC-mediated "social brakes" are weak; the child knows the rule but cannot apply it in the moment

Several inattentive or hyperactive-impulsive symptoms were present prior to age 12 years ^[2]

Why age 12? — DSM-5 relaxed this from the DSM-IV threshold of age 7, based on evidence that (a) many patients (especially the predominantly inattentive type) are not identified until later in childhood, and (b) retrospective recall of symptom onset before age 7 is unreliable. Age 12 captures nearly all true ADHD cases (98% by age 16 ^[2]) while reducing false negatives.

Several inattentive or hyperactive-impulsive symptoms are present in ≥ 2 settings (e.g., at home, school or work; with friends or relatives; in other activities) ^[2]

Why ≥ 2 settings? — This distinguishes ADHD from situation-specific problems. A child who is "inattentive" only in maths class likely has a maths-specific learning disorder, not ADHD. A child who is hyperactive only at home but calm at school may have a family dynamics issue. True ADHD is pervasive because the underlying neurobiological deficit goes with the child everywhere.

There is clear evidence that the symptoms interfere with, or reduce the quality of, social, academic, or occupational functioning ^[2]

Why functional impairment? — Many people have some inattention or restlessness. You only diagnose a disorder when the symptoms cross the threshold into causing meaningful impairment. This prevents pathologising normal variation.

The symptoms do not occur exclusively during the course of schizophrenia or another psychotic disorder and are not better explained by another mental disorder (e.g., mood disorder, anxiety disorder, dissociative disorder, personality disorder, substance intoxication or withdrawal) ^[2]

Why this criterion? — As discussed in the differential diagnosis section, many conditions mimic ADHD. This criterion forces the clinician to consider alternatives. Note the word "exclusively" — ADHD can co-occur with these conditions; it just cannot be diagnosed if the symptoms are entirely explained by the other condition.

Specify presentation: (1) Predominantly Inattentive, (2) Predominantly Hyperactive-Impulsive, (3) Combined ^[2]

Also specify:

In partial remission — if full criteria were previously met but fewer than full criteria have been met for the past 6 months, yet symptoms still cause impairment
Severity: Mild / Moderate / Severe

Both impaired attention and overactivity should be present, and should be evident in > 1 situations. They should be diagnosed only if they are excessive for the child's age and IQ. ^[2]

Key differences from DSM-5:

Feature	ICD-10	DSM-5
Term	Hyperkinetic Disorder (F90)	Attention-Deficit/Hyperactivity Disorder
Required domains	Both inattention and overactivity must be present ^[1]^[2]	Either inattention or hyperactivity-impulsivity (or both) ^[1]^[2]
Age of onset	Before age 6 ^[2]	Before age 12 ^[2]
Predominantly inattentive subtype	Not formally recognised under F90	Recognised as a separate presentation
Strictness	Narrower definition → captures more severe cases	Broader definition → captures the full spectrum
Conduct disorder	Symptoms of conduct disorder are neither exclusion nor inclusion criteria for the main diagnosis, but their presence or absence constitutes the basis for the main subdivision ^[2] (F90.0 vs F90.1)	CD is coded separately as a comorbidity

The characteristic behaviour problems should be of early onset (before age 6 years) and long duration. However, before the age of school entry, hyperactivity is difficult to recognise because of the wide normal variation: only extreme levels should lead to a diagnosis in preschool children. ^[2]

Associated features include disinhibition in social relationships, recklessness in dangerous situations, impulsive flouting of social rules. ^[2]

Learning disorders and motor clumsiness occur with undue frequency, and should be noted separately (under F80–F89) when present; they should not, however, be part of the actual diagnosis of hyperkinetic disorder. ^[2]

ICD-10 vs DSM-5 — Exam Must-Know

The key conceptual difference: ICD-10 (Hyperkinetic Disorder) is stricter — it requires both inattention and hyperactivity, onset before age 6, and essentially captures only the combined/hyperactive subtypes. DSM-5 is broader — it allows either domain, onset before age 12, and recognises the predominantly inattentive presentation. In clinical practice, DSM-5 criteria are more commonly used for ADHD specifically. ICD-11 has now harmonised with DSM-5 by recognising all three presentations.

ICD-11 has made several important changes to align with DSM-5:

Now uses the term "ADHD" (not "Hyperkinetic Disorder")
Recognises three presentations: predominantly inattentive, predominantly hyperactive-impulsive, combined
Does not specify a strict age threshold — instead requires onset "during the developmental period" (generally childhood)
Allows a dimensional approach to symptom severity
Explicitly allows comorbid diagnosis with ASD

Diagnosis of hyperkinetic disorder can still be made in adult life. The grounds are the same, but attention and activity must be judged with reference to developmentally appropriate norms. ^[2]

Key points specific to adult diagnosis:

DSM-5 requires only ≥ 5 symptoms (instead of ≥ 6) for age ≥ 17 — because adults compensate and symptoms manifest differently
Retrospective confirmation of childhood onset is essential — corroborated by school reports, parental recall, or collateral history
Hyperactivity is internalised (inner restlessness, workaholism) rather than overt motor overactivity
Impulsivity manifests as low frustration tolerance, rash decisions, addictive tendencies

When hyperkinesis was present in childhood, but has disappeared and been succeeded by another condition, such as dissocial personality disorder or substance abuse, the current condition rather than the earlier one is coded. ^[2]

Diagnostic Algorithm

Step-by-Step Clinical Assessment Pathway

The assessment of ADHD follows a systematic pathway. Let me lay this out as a practical clinical algorithm:

Suspicion: detected at primary care (but not diagnosed) ^[2]

Referral typically comes from parents, teachers, or school counsellors who notice the child is "not keeping up" or "always in trouble"
In adults, self-referral is common ("I think I might have ADHD" — increasingly common with public awareness)

Subsequent approach ^[2]:

Mild: advice, support, watchful waiting; offer group parent training

Moderate: refer to specialists at school age for behavioural therapy or medications

Severe: refer to specialists for medications as 1st choice

This is the core diagnostic process. It involves multiple sources of information — you never diagnose ADHD from a single consultation or a single informant.

Detailed Assessment Components

The clinical interview is the cornerstone of ADHD diagnosis. You need information from multiple informants because behaviour varies across settings, and a single observer may miss or overemphasise certain features.

Interview with the child/adolescent:

Observe the child's behaviour during the consultation (though some children with ADHD behave well in the novelty of a 1:1 clinical setting — this does not rule out ADHD)
Ask about their own experience: difficulties at school, friendships, how they feel about their behaviour
In adolescents/adults: self-report of concentration difficulties, organisational problems, impulsivity

Interview with parents/carers:

Domain	Sample Questions from Assessment ^[2]
Attention span	How short was attention span over day-to-day tasks, e.g., packing schoolbags, completing homework?
Homework	How long does it take to finish homework? How does it compare with his peers? Does he need any 1-on-1 supervision?
Play behaviour	When playing with toys, does he often shift toys and not try to explore and has short interest in new toys?
Group activities	In group games, is he attentive, e.g., listen to coach's instructions?
Distractibility	How easily distracted is he? Does he play with stationery, toys, books, fingers? Does he go away from seat? What happens when there is any noise around?
Daydreaming	Any daydreaming? ^[2]
Listening	Does he have a good attention when others are chatting or over the phone? ^[2]
Intrusiveness	Does he try to give comment when not asked? ^[2]
Waiting ability	Is he unable to wait when asked, but often forgets what to say afterwards when asked to wait? ^[2]

Interview with teachers:

Teacher observations provide essential information about the school setting — the primary arena where inattention and hyperactivity become functionally impairing
Teacher rating scales (see below) are critical for confirming pervasiveness

Rating scales are supplementary tools — they do not make the diagnosis on their own but provide structured, quantifiable information.

Rating Scale	Informant	Content	Role in Assessment
Conners Rating Scales (CRS-3)	Parent and Teacher versions	ADHD symptoms, ODD, cognitive problems, social problems	Most widely used ADHD-specific scale; provides T-scores normed by age and sex; useful for monitoring treatment response
SNAP-IV (Swanson, Nolan, and Pelham)	Parent and Teacher	Directly maps onto DSM criteria for inattention, hyperactivity-impulsivity, and ODD	Free, quick (18 items for ADHD), easy to score; excellent for tracking symptom change
SDQ (Strengths and Difficulties Questionnaire)	Parent, Teacher, Self (age ≥ 11)	Emotional, conduct, hyperactivity/inattention, peer problems, prosocial behaviour	Broad screening tool (not ADHD-specific); useful for detecting comorbidities; widely used in UK/HK
Vanderbilt Assessment Scales	Parent and Teacher	ADHD symptoms + ODD, CD, anxiety, depression, and academic performance	Comprehensive, free, includes functional impairment and comorbidity screening
WURS (Wender Utah Rating Scale)	Self (retrospective)	Childhood ADHD symptoms recalled by adults	Used in adult ADHD assessment to help establish childhood onset
ASRS (Adult ADHD Self-Report Scale)	Self (adults)	18 items mapping to DSM-5 criteria for adults	WHO-developed screening tool for adult ADHD; quick (6-item screener available)
DIVA (Diagnostic Interview for ADHD in Adults)	Semi-structured interview	Systematic assessment of all DSM criteria in childhood and adulthood	Gold-standard structured interview for adult ADHD diagnosis

Rating Scales Are Supportive, Not Diagnostic

A common exam mistake: rating scales do not diagnose ADHD. They are tools that help quantify symptoms and provide information from multiple informants. The diagnosis is made by a clinician integrating information from clinical interview, collateral history, rating scales, developmental history, and exclusion of differential diagnoses. A child can score high on Conners and not have ADHD (e.g., if symptoms are caused by anxiety), or score borderline but clearly have ADHD with significant functional impairment.

Area	What to Assess	Why
Pregnancy and birth	Maternal smoking, alcohol, substance use; prematurity; low birth weight; obstetric complications	These are risk factors for ADHD (perinatal insults to developing PFC) ^[2]
Developmental milestones	Motor, language, social milestones	Delays may suggest broader neurodevelopmental disorder (ASD, ID); clumsiness, language delay, abnormalities of speech suggest neurodevelopmental impairment ^[2]
Family psychiatric history	ADHD, mood disorders, anxiety, substance abuse, ASD, learning difficulties in 1st-degree relatives	Heritability ~70–80%; ~1/4 of siblings have ADHD ^[2]
Early behaviour	Temperament as infant/toddler, behaviour at nursery, early reports from preschool	Establishes whether symptoms were present before age 6/12
Psychosocial context	Family structure, parenting style, ACEs, socioeconomic status, school environment	Identifies maintaining/exacerbating factors; rules out purely environmental causes (e.g., extreme deprivation)

The physical examination in ADHD assessment serves two purposes: (1) exclude medical mimics, and (2) establish a baseline before starting medication.

Examination	Purpose	Key Findings to Note
Height, weight, BMI (plotted on growth chart)	Baseline for monitoring stimulant side effects (appetite suppression → growth deceleration)	Note percentile; will need serial monitoring
Blood pressure and heart rate	Baseline for stimulant cardiovascular monitoring	Exclude pre-existing hypertension or tachycardia
Cardiovascular examination	Exclude structural heart disease before starting stimulants	Murmurs, irregular rhythm → further investigation before prescribing
Thyroid examination	Exclude hyperthyroidism as a mimic	Goitre, exophthalmos, tremor, tachycardia
Neurological examination	Assess for soft neurological signs; exclude neurological conditions	Coordination difficulties (cerebellar signs), motor tics, asymmetric reflexes; clumsiness suggests neurodevelopmental impairment ^[2]
Dysmorphic features	Screening for genetic syndromes associated with ADHD-like features	Fetal alcohol syndrome (smooth philtrum, thin upper lip, short palpebral fissures); Fragile X (long face, large ears, macroorchidism); 22q11 deletion; Williams syndrome
Skin examination	Screen for neurocutaneous syndromes	Café-au-lait spots (NF1 — associated with ADHD), ash-leaf macules (tuberous sclerosis), port-wine stains
Vision and hearing screening	Exclude sensory impairments mimicking inattention	Refractive errors, conductive hearing loss

Investigation Modalities

There is no diagnostic test for ADHD. Investigations are used to:

Exclude medical mimics (medical differential diagnosis)
Identify comorbidities (especially learning disorders)
Establish pre-treatment baselines (before starting pharmacotherapy)
Support the clinical impression (neuropsychological testing in ambiguous cases)

Investigation	Indication	Key Findings / Interpretation
Thyroid Function Tests (TFTs)	New presentation of inattention/hyperactivity, especially if systemic symptoms present	↑ T4/T3 + ↓ TSH → hyperthyroidism mimicking ADHD; rare but must be excluded. Resistance to thyroid hormone (RTH) syndrome is a rare genetic cause of ADHD + thyroid abnormalities
Full Blood Count (FBC) + Iron studies	Suspected nutritional deficiency; restless legs symptoms; pre-treatment baseline	Iron deficiency (↓ ferritin) → fatigue, restlessness, impaired cognition. Iron is a cofactor for tyrosine hydroxylase (the rate-limiting enzyme in dopamine synthesis), so low iron → ↓ dopamine → ADHD-like symptoms
Lead level	Suspected environmental exposure (old housing, industrial areas)	↑ Lead → disrupts dopaminergic neurotransmission → inattention, hyperactivity, cognitive impairment. Should be considered in high-risk populations
Urine drug screen	Adolescents/adults with new or worsening symptoms; suspected substance use	Positive for stimulants, cannabis, etc. → substance-induced ADHD-like symptoms
ECG	Before starting stimulant medication, especially if: personal/family history of cardiac disease, syncope, palpitations, sudden cardiac death in family	Prolonged QTc, pre-excitation (WPW), Brugada pattern, ventricular hypertrophy → contraindication or caution with stimulants. Stimulants have mild sympathomimetic effects → ↑ HR, ↑ BP, and rarely arrhythmias in those with pre-existing cardiac conditions
Echocardiogram	If ECG abnormal or clinical suspicion of structural heart disease	Structural anomalies that may contraindicate stimulant use
Audiometry	If hearing impairment suspected	Conductive or sensorineural hearing loss → child cannot hear teacher → appears inattentive
Vision testing	If visual impairment suspected	Refractive errors → difficulty seeing board/worksheets → appears inattentive
EEG	Suspected seizure disorder (absence epilepsy mimicking inattention — the child "blanks out")	3 Hz spike-and-wave in absence epilepsy. Note: routine EEG is NOT indicated for ADHD itself; only if clinical suspicion of epilepsy
Brain MRI	NOT routine; only if focal neurological signs, concern about structural lesion, or atypical presentation	Imaging studies show ↓ volume/cortical thickness, especially in grey matter of basal ganglia ^[2] — but these are research findings and not clinically diagnostic; MRI is normal or non-specifically abnormal in individual ADHD patients

Test Type	What It Measures	Role in ADHD Assessment
IQ Testing (WISC-V for children; WAIS-IV for adults)	Full-scale IQ, verbal comprehension, perceptual reasoning, working memory, processing speed	Identifies intellectual disability or giftedness (both can mimic ADHD); ADHD patients often show a characteristic pattern: low Working Memory Index and Processing Speed Index relative to other indices (this is supportive, not diagnostic)
Continuous Performance Test (CPT) — e.g., TOVA, Conners CPT	Sustained attention, impulsivity, response time variability	Measures omission errors (inattention), commission errors (impulsivity), and reaction time variability (attentional consistency). Sensitivity ~70–80% but not specific enough to diagnose alone; useful in ambiguous cases
Trail Making Test (Part A and B)	Processing speed, cognitive flexibility, task-switching	Part B specifically tests executive function (set-shifting); ADHD patients are often slow and make more errors on Part B
Stroop Test	Inhibitory control (the ability to suppress a prepotent response)	ADHD patients show an exaggerated "Stroop effect" — greater difficulty inhibiting the automatic reading response
Wisconsin Card Sorting Test (WCST)	Cognitive flexibility, set-shifting, response to feedback	ADHD patients may show more perseverative errors (difficulty shifting strategy when feedback changes)
Academic Achievement Tests (e.g., WIAT)	Reading, writing, mathematics achievement relative to IQ	Identifies specific learning disorders (reading disorder, maths disorder) — these occur with undue frequency and should be noted separately ^[2]; achievement significantly below IQ → specific LD

Neuropsychological Testing — When and Why?

Neuropsychological testing is not required to diagnose ADHD in straightforward cases. It is most useful when:

The clinical picture is ambiguous (e.g., inattentive only, no hyperactivity, high IQ)
You need to differentiate ADHD from a learning disorder or intellectual disability
You need to quantify the executive function deficit for educational accommodations
There is treatment resistance and you need to understand the cognitive profile better

A classic ADHD neuropsychological profile: relatively intact IQ with disproportionately low Working Memory Index and Processing Speed Index, elevated CPT omission and commission errors, and poor performance on tests of inhibitory control (Stroop, Go/No-Go).

Before starting pharmacotherapy (especially stimulants), you must establish baselines:

Parameter	Why	Frequency of Monitoring
Height and weight	Stimulants suppress appetite → risk of growth deceleration	Every 3–6 months on stimulants; plot on growth chart
Blood pressure and heart rate	Stimulants have mild sympathomimetic effects → ↑ HR, ↑ BP	Before starting; every visit for the first 3 months; then every 3–6 months
ECG	Exclude pre-existing cardiac conduction abnormalities	Before starting stimulants if indicated (varies by guideline; NICE recommends only if cardiac risk factors; some centres do it routinely)
Liver function tests	Required before starting atomoxetine (rare risk of hepatotoxicity)	Baseline; then if symptoms suggest hepatic dysfunction

Let me distil this into the practical exam framework:

Component	Establishes	Source
Clinical interview (child + parents + teachers)	Symptom presence, pervasiveness, onset, functional impairment	Core of diagnosis
Rating scales (Conners, SNAP-IV, SDQ)	Quantification of symptoms from multiple informants	Supportive
Developmental/family history	Early onset, genetic risk, perinatal risk factors	Supports Criteria B
Physical examination	Excludes medical mimics; establishes pre-treatment baselines	Essential
Investigations (TFTs, FBC, lead, ECG, audiometry, vision)	Excludes specific medical causes	As indicated
Neuropsychological testing	Cognitive profiling; identifies comorbid learning disorders; supports ambiguous cases	Not routine; as indicated
DSM-5/ICD criteria application	Formal diagnostic threshold	Required

High Yield Summary

ADHD is a clinical diagnosis — no single test confirms it. Diagnosis requires integration of clinical interview, collateral history from multiple informants, rating scales, developmental history, and exclusion of differential diagnoses.
DSM-5 Criteria: ≥ 6/9 symptoms (≥ 5 if age ≥ 17) in inattention and/or hyperactivity-impulsivity; ≥ 6 months duration; onset before age 12; present in ≥ 2 settings; functional impairment; not better explained by another disorder.
ICD-10 (Hyperkinetic Disorder): Stricter — requires BOTH inattention AND hyperactivity; onset before age 6. ICD-11 has aligned with DSM-5.
Rating scales (Conners, SNAP-IV, SDQ): Supportive but NOT diagnostic on their own. Need parent AND teacher versions to confirm pervasiveness.
Investigations are to exclude mimics and establish pre-treatment baselines: TFTs (thyroid), FBC + iron (deficiency → ↓ dopamine), lead level, audiometry/vision, ECG (pre-stimulant).
Neuropsychological testing: Not routine. Useful for ambiguous cases, comorbid learning disorders, educational accommodations. Classic ADHD profile: low working memory + processing speed indices relative to full-scale IQ.
Pre-treatment baselines: Height, weight, BP, HR, ECG (if cardiac risk factors), LFTs (if starting atomoxetine).
Multiple informant approach: ALWAYS get information from parents AND teachers — you need to confirm pervasiveness across settings.
Adult ADHD: Requires retrospective confirmation of childhood onset; threshold lowered to ≥ 5 symptoms for age ≥ 17; use DIVA or ASRS for structured assessment.
Key difference between ICD-10 and DSM-5: ICD-10 requires both domains + onset < 6y (stricter); DSM-5 allows either domain + onset < 12y (broader). ICD-11 now aligns with DSM-5.

Active Recall - ADHD Diagnostic Criteria, Algorithm & Investigations

Management of ADHD

Before diving into specifics, let's understand why ADHD management is structured the way it is. From first principles:

ADHD is a chronic neurodevelopmental condition, not an acute illness. Management is long-term — think of it like managing hypertension or diabetes, not treating pneumonia.
The neurobiological deficit (hypo-dopaminergic/noradrenergic fronto-striatal circuits) is amenable to pharmacological correction — this is why medications are so effective.
The functional impairment spans multiple domains (academic, social, family, emotional) — this is why psychosocial interventions are needed alongside medication.
Comorbidities are the rule, not the exception (~50%) — these must be addressed simultaneously or treatment will be suboptimal.

Approach to management: individualised comprehensive multimodal treatment programme ^[2]

Pre-school: usually behaviour therapy as mainstay

School age: usually a combination of medications + psychosocial therapy

Management of comorbidities, e.g., ASD, ODD/CD, mood disorder, anxiety disorders ^[2]

The MTA Study (Multimodal Treatment Study of Children with ADHD, 1999) — the largest and most influential ADHD treatment trial — established that:

Medication alone was superior to behavioural therapy alone for core ADHD symptoms
Combined treatment (medication + behavioural therapy) was superior to medication alone for certain outcomes (comorbid anxiety, oppositional behaviour, parent-child relationships, academic achievement)
Both medication and combined treatment were superior to routine community care

This is the evidence base behind the multimodal approach.

Stepwise Approach by Severity and Age

This is the foundation of management. Before any specific intervention, the child, family, and school must understand what ADHD is and what it is not.

Component	Content	Why It Matters
For parents	ADHD is a neurobiological condition, not "bad parenting" or "laziness." Explain the dopamine/noradrenaline model simply. Set realistic expectations.	Reduces parental guilt and blame; improves treatment adherence; empowers parents as partners
For the child	Age-appropriate explanation: "Your brain works differently — it's harder for you to put the brakes on." Normalise the condition.	Reduces self-blame and shame; builds self-esteem; increases engagement with treatment
For teachers/school	Explain the condition, the need for accommodations, and the expected effects of treatment	Ensures pervasive support; prevents punitive approaches that worsen outcomes

Step 1: By Age Group

Pre-school: usually behaviour therapy as mainstay ^[2]

Why not medications first in preschoolers?

The evidence base for stimulant safety and efficacy is stronger for school-age children
Preschool ADHD has a wider differential (normal developmental variation is broad at this age)
Behavioural interventions are effective at this age because parents can control more of the environment
Side effects (appetite suppression, growth deceleration) are of greater concern in younger children
If behavioural therapy is insufficient and symptoms are moderate-severe, low-dose methylphenidate can be considered by a specialist (NICE 2024 guidelines)

Management is guided by severity:

Severity	First-Line Approach	Rationale
Mild	Advice, support, watchful waiting; offer group parent training ^[2]; school accommodations	Many mild cases can be managed with environmental modifications and behavioural strategies alone
Moderate	Refer to specialists at school age for behavioural therapy or medications ^[2]	The MTA study showed medication is more effective than behavioural therapy alone for core symptoms, but combined treatment gives the best all-round outcomes
Severe	Refer to specialists for medications as 1st choice ^[2]	When functional impairment is severe, the fastest and most effective way to restore function is medication. Behavioural therapy alone is insufficient for severe ADHD.

1st line: Medication (methylphenidate or lisdexamfetamine) + psychoeducation
Adjunctive: CBT adapted for adult ADHD (focuses on organisational skills, time management, emotional regulation, cognitive restructuring)
Coaching: ADHD coaching targets practical daily-life skills
NICE (2024) recommends medication as first-line for adults (behavioural therapy alone is insufficient in most adult cases)

Pharmacological Management

Medications: very effective (most effective among all psychotropics) → more effective than psychosocial treatment ^[2]

This is a remarkable statement and worth emphasising: ADHD medications have among the largest effect sizes of any psychotropic medication in all of psychiatry. Stimulants for ADHD (effect size ~1.0) are more effective than SSRIs for depression (effect size ~0.3–0.5), antipsychotics for schizophrenia (effect size ~0.5), or lithium for bipolar disorder.

A. Stimulants (First-Line)

"Methyl-phenidate" → a piperidine derivative structurally related to amphetamine

MoA: ↑ availability of central dopamine and noradrenaline → CNS stimulant ^[2]

Mechanism in detail: Methylphenidate primarily blocks the dopamine transporter (DAT) and the noradrenaline transporter (NET) at the presynaptic terminal. By preventing reuptake, it increases the concentration of dopamine and noradrenaline in the synaptic cleft, particularly in the prefrontal cortex and striatum. This boosts the "signal-to-noise ratio" of neural signalling in the fronto-striatal circuit → improved inhibitory control, sustained attention, and working memory.

Why does a "stimulant" calm down a hyperactive child? — The paradox is explained by the inverted-U model: the ADHD brain is understimulated in the PFC. The stimulant brings catecholamine levels from "too low" to "optimal," thereby activating the brain's inhibitory control systems. The child becomes calmer because the executive "brakes" are now powered on.

Efficacy: very effective with effect size of 1.0; ↓ restlessness, ↓ aggression, ↑ attention (but ? long-term outcome) ^[2]

The question mark about long-term outcome is important: while stimulants are highly effective in the short-to-medium term, the MTA study's long-term follow-ups showed that initial medication advantages diminished over time (possibly due to adherence issues, dose adjustments, and the natural course of the condition).

Formulation	Drug Type	Onset	Duration	Doses Per Day	Common Side Effects	Uncommon Side Effects	Effect Size
Ritalin (methylphenidate IR)	CNS stimulant	20–60 min	1–4 hours	More than once daily	Decreased appetite, weight loss, insomnia, headache, abdominal pain, irritability, mood swing	Motor tics, tachycardia	1.0
Ritalin LA (methylphenidate ER)	CNS stimulant	20–60 min	8 hours	Once daily	Side effects similar to Ritalin		1.0
Concerta (methylphenidate OROS)	CNS stimulant	30 min – 2 hours	12 hours	Once daily	Side effects similar to Ritalin, but relatively milder		1.0

^[2]

Dosing: avoid dosing after 5pm in primary school and 6pm in secondary school → ↓ insomnia ^[2]

Why? — Methylphenidate's stimulant effect interferes with sleep initiation. If the last dose wears off by bedtime, the child can fall asleep. Dosing too late in the day causes the stimulant to still be active at bedtime → insomnia → next-day fatigue → worsened ADHD symptoms. This creates a vicious cycle.

Short-acting: require multiple dosing but easier to titrate to fit the child's schedule (e.g., allow off-drugs at home in the afternoon → avoid insomnia) ^[2]

Long-acting: can be dosed once daily but may have ↑ side effects later in the day ^[2]

Practical choice: Short-acting (Ritalin IR) is useful for initial titration and when flexible dosing is needed (e.g., medication-free weekends or afternoons). Long-acting (Ritalin LA, Concerta) is preferred for maintenance because:

Once-daily dosing → better adherence (the child doesn't need to take medication at school)
More consistent blood levels → smoother symptom control without peaks and troughs
Avoids the stigma of taking medication in front of peers at school

Side effects: irritability, depression, insomnia, poor appetite (with ↓ height/weight growth), ↑ tic disorders ^[2]

Side Effect	Mechanism	Management
↓ Appetite / weight loss	DA in the hypothalamic appetite centres suppresses hunger signals	Give medication with/after meals; encourage calorie-dense breakfast before medication kicks in; "drug holidays" (weekends/school holidays) to allow catch-up growth
Insomnia	Stimulant effect on ascending reticular activating system; DA/NA in wake-promoting circuits persist into evening	Avoid late dosing; switch to shorter-acting formulation if long-acting causing issues; consider adding melatonin for sleep onset
Growth deceleration	Combination of ↓ caloric intake + possible direct GH suppression (controversial)	Monitor height/weight on growth charts every 3–6 months; consider drug holidays during school vacations; generally, final adult height is minimally affected (1–3 cm reduction)
Irritability / mood lability	"Rebound effect" as medication wears off → acute catecholamine drop; or dose too high → overstimulation	Smooth the transition with overlapping doses or switch to longer-acting formulation; reduce dose if overstimulated
↑ Tic disorders	Stimulants may unmask or exacerbate pre-existing tic vulnerability (dopaminergic activation of basal ganglia) ^[2]	Monitor; if tics emerge or worsen, consider reducing dose, switching to atomoxetine, or adding an alpha-2 agonist (clonidine/guanfacine) which treats both ADHD and tics
↑ HR, ↑ BP	Sympathomimetic effect (peripheral NA release)	Monitor HR/BP regularly; avoid in uncontrolled hypertension or significant cardiac disease
Headache, abdominal pain	Sympathomimetic GI effects; tension-type headache from vasoconstriction	Usually transient; manage symptomatically; may resolve with dose adjustment

Contraindication	Reason
Structural cardiac disease, cardiomyopathy, serious arrhythmias	Sympathomimetic effects → ↑ risk of sudden cardiac death in those with underlying structural heart disease
Uncontrolled hypertension	Stimulants ↑ BP → risk of hypertensive crisis
Phaeochromocytoma	Catecholamine-secreting tumour + exogenous catecholamine enhancement → hypertensive emergency
Hyperthyroidism	Already hypersympathetic state → additive effects
Concurrent MAOIs	Both increase catecholamines → risk of hypertensive crisis; must wait ≥ 14 days after stopping MAOIs
Psychosis	Dopamine agonism can exacerbate psychotic symptoms
Caution: Tic disorders	May unmask or worsen tics (though this is debated — many children with tics tolerate stimulants well under monitoring)
Caution: Family history of substance abuse	Use when stimulants are not appropriate, e.g., FHx of SA ^[2] — diversion/misuse risk; consider non-stimulant alternatives

Lisdexamfetamine (Vyvanse/Elvanse): a prodrug — "lis" = lysine; the drug is inactive until cleaved by red blood cell enzymes to release d-amphetamine. This provides a smoother onset and longer duration (~13 hours), and reduced abuse potential (cannot be "snorted" or injected effectively because it requires enzymatic activation).
- MoA: Promotes release of DA and NA from presynaptic terminals (in addition to reuptake inhibition) → more potent than methylphenidate
- Effect size: ~1.0 (comparable to methylphenidate)
- NICE (2024): lisdexamfetamine is 1st-line alongside methylphenidate for adults; 2nd-line for children if methylphenidate is not tolerated or ineffective
- Available in HK
Dexamfetamine (Dexedrine): short-acting amphetamine; available but less commonly used as first-line

Dexmethylphenidate (Focalin) — mentioned in notes as an alternative psychostimulant ^[2]. This is the pharmacologically active d-enantiomer of methylphenidate (the l-enantiomer is thought to be less active). Available in some jurisdictions but less commonly used in HK.

B. Non-Stimulants (Second-Line)

"Atomoxetine" → a selective noradrenaline reuptake inhibitor (NRI). Though sometimes classified as an SNRI, it has minimal serotonergic activity at therapeutic doses — it primarily blocks the NET.

Property	Detail
Drug type	Non-stimulant ^[2]
MoA	↑ availability of central dopamine and noradrenaline ^[2] — specifically, by blocking NET in the PFC. In the PFC, there is sparse DAT expression, so DA clearance in the PFC actually occurs via NET. Therefore, blocking NET in the PFC increases both NA and DA there — clever pharmacology!
Onset	4–6 weeks ^[2] — much slower than stimulants (which work within 30–60 minutes). This is because atomoxetine works through gradual receptor adaptation, similar to SSRIs in depression
Duration	24 hours ^[2] — continuous coverage; no "rebound" effect
Dosing	Once daily ^[2]
Efficacy	Effect size ~0.7 ^[2] — less effective than stimulants (1.0) but still clinically meaningful
Common side effects	Epigastric discomfort, nausea/vomiting, sedation, decreased appetite, dizziness, mood swing ^[2]
Uncommon side effects	Deranged liver function ^[2]

Use: used when stimulants are not appropriate, e.g., FHx of SA, tic disorder, unresponsive to stimulants ^[2]

Why is atomoxetine preferred over stimulants in these situations?

FHx of substance abuse: Atomoxetine has zero abuse potential (it is not a controlled substance). Stimulants, being dopaminergic, have euphorigenic and reinforcing properties → risk of misuse or diversion, especially in families with substance abuse ^[2]
Tic disorder: Atomoxetine does not exacerbate tics (and may modestly improve them), whereas stimulants can worsen tics in some patients
Comorbid anxiety: Atomoxetine may have anxiolytic effects (NA modulation in the PFC can reduce anxiety), making it preferred when ADHD coexists with significant anxiety
Need for 24-hour coverage: The continuous action means coverage extends to evenings and mornings (homework time, family time) without multiple dosing

Serious rare side effect — Hepatotoxicity:

Severe liver damage (1/50,000) ^[2]

This is why baseline LFTs are recommended before starting atomoxetine. Patients/parents should be counselled to report signs of hepatic dysfunction: jaundice, dark urine, abdominal pain, unexplained nausea, pruritus.

Other important safety concern — Suicidality:

Atomoxetine carries an FDA black box warning for increased suicidal ideation in children and adolescents (similar to SSRIs)
This is rare but must be monitored, especially in the first few months of treatment

Contraindication	Reason
Concurrent MAOIs	Both enhance catecholamines → hypertensive risk
Narrow-angle glaucoma	NA-mediated mydriasis can precipitate acute angle closure
Severe hepatic impairment	Hepatically metabolised; risk of accumulation and toxicity
Phaeochromocytoma	NA enhancement in the setting of a catecholamine-secreting tumour

α₂-agonists, e.g., clonidine, guanfacine ^[2]

These are sometimes called "third-line" agents but are increasingly used as adjunctive therapy alongside stimulants.

Property	Clonidine	Guanfacine (Intuniv)
MoA	Non-selective α₂-agonist → stimulates presynaptic α₂A-receptors in the locus coeruleus → ↓ NA firing; stimulates postsynaptic α₂A-receptors in the PFC → improves signal transduction in prefrontal circuits → ↑ working memory, ↓ distractibility	Selective α₂A-agonist → more targeted action at PFC postsynaptic receptors; less sedation than clonidine because it doesn't hit other α₂ subtypes as much
Efficacy	Modest (effect size ~0.3–0.5); primarily ↓ hyperactivity, impulsivity, aggression; less effect on inattention	Moderate (effect size ~0.5–0.6); improves both inattention and hyperactivity-impulsivity
Indications	Adjunct to stimulant when partial response; monotherapy if stimulants/atomoxetine not tolerated; comorbid tic disorder (clonidine ↓ tics); comorbid insomnia (sedative effect useful for stimulant-induced insomnia)	Extended-release guanfacine (Intuniv) is FDA-approved as monotherapy or adjunct for ADHD in children ≥ 6 years
Side effects	Sedation (major), hypotension, bradycardia, dry mouth, rebound hypertension if stopped abruptly	Sedation (less than clonidine), hypotension, headache, fatigue
Key caution	Must taper gradually — abrupt cessation → rebound hypertension (α₂-receptors have been downregulated; sudden loss of α₂ agonism → unopposed sympathetic tone)	Same caution regarding tapering

Why do α₂-agonists work in ADHD? From first principles: the α₂A-receptor in the PFC, when stimulated, strengthens the connections in prefrontal networks. Arnsten's research demonstrated that optimal PFC function requires moderate levels of NA acting at α₂A-receptors. These drugs essentially "tune" the PFC by optimising NA signalling — different from stimulants but targeting the same functional outcome.

Non-Pharmacological Management

Non-pharmacological interventions ^[2]:

Parent management training (PMT): regarded as the most effective behavioural therapy ^[2]

Aim: identify problem situations and precipitating factors; offer strategies to deal with them; enhance positive and limited negative parent-child interactions ^[2]

Why is PMT the most effective behavioural intervention? Because parents are the most consistent environmental influence in a young child's life. If you change how parents respond to behaviour, you change the reinforcement patterns that maintain maladaptive behaviour. PMT is based on operant conditioning principles:

Strategy	How It Works	Behavioural Principle
Reward system	Offer reward for desirable behaviour → positive reinforcement ^[2]	Behaviours that are positively reinforced (rewarded) increase in frequency. The child learns: "When I sit still and finish my homework, I earn a star."
Time-out	Ask children to stay in isolated time-out area for a period of time for bad behaviour ^[2]	Removal of positive reinforcement (attention, play, interaction) contingent on undesirable behaviour. The child learns: "When I hit my sister, I lose access to fun things." Important: time-out is NOT a punishment — it is the removal of reinforcement.
Response cost system	Withdrawing rewards or privileges when unwanted or problem behaviour occurs ^[2]	Negative punishment (removal of a desired stimulus) → the undesirable behaviour decreases. Example: losing screen time for not following instructions.
Behaviour modelling	Behaviour modelling ^[2]	Parents model the desired behaviour → child learns through observational learning (Bandura's social learning theory).

Behavioural treatment in classroom: similar to the approach used at home with parents ^[2]

Goal: ↓ inattention and disruptive behaviour ^[2]

ADHD is a type of special education need (SEN), to be provided under inclusion education policy ^[2]

This is particularly relevant in Hong Kong, where the inclusion education policy mandates that schools provide accommodations for children with SEN, including ADHD.

Specific school accommodations ^[2]:

Accommodation	How It Helps	Behavioural/Cognitive Basis
Ensure structured and predictable routines	Reduces cognitive load; the child doesn't need to rely on impaired executive function to figure out "what comes next"	Externalising the executive function — the structure substitutes for the child's weak internal organiser
Employ cost-response token economy systems, e.g., star charts	Tangible, immediate reinforcement for on-task behaviour	ADHD children have delay aversion — they need immediate rewards, not distant ones. Token systems provide frequent, immediate positive reinforcement
Use of daily report cards	Bridge between school and home; parents can reinforce school behaviour at home	Increases consistency of behavioural contingencies across settings
Teach organisation and work/study skills	Explicit instruction in strategies that neurotypical children develop spontaneously	Compensates for the executive function deficit; teaches concrete strategies (checklists, planners, breaking tasks into steps)

Additional school accommodations (not listed in notes but clinically important):

Preferential seating (front of class, away from windows/doors) → reduces distracting stimuli
Frequent breaks → prevents attentional fatigue
Extended time on tests → allows for slower processing speed
Reduced homework load → prevents overwhelm and family conflict
Written instructions (in addition to verbal) → compensates for working memory deficit

Other interventions, e.g., social skills training, cognitive training, cognitive-behavioural training ^[2]

Intervention	Target	Evidence
Social Skills Training	Teaches turn-taking, conversation skills, conflict resolution — addresses the social impairment that arises from impulsivity	Modest evidence; most effective when combined with generalisation strategies (i.e., practised in real-world settings, not just a therapy room)
Cognitive-Behavioural Therapy (CBT)	Particularly for adolescents and adults: teaches organisational skills, time management, emotional regulation, cognitive restructuring	Strong evidence in adult ADHD (Safren model); modest evidence in children (children's metacognitive skills may not be mature enough for full CBT)
Cognitive Training (e.g., working memory training)	Computerised programs (e.g., Cogmed) that aim to strengthen working memory through repeated practice	Evidence is mixed; may improve working memory scores on tests but does not consistently transfer to real-world ADHD symptom improvement
Neurofeedback	Trains patients to modify their EEG patterns (e.g., increasing beta/theta ratio)	Inconclusive evidence; not recommended as a primary treatment by NICE or AAP; may be a useful adjunct in some cases
Exercise	Regular physical activity increases BDNF, dopamine, and noradrenaline in the brain	Growing evidence that regular aerobic exercise has modest beneficial effects on ADHD symptoms; should be encouraged as part of a healthy lifestyle
Dietary interventions	Elimination diets (removing artificial colourings/additives); omega-3 supplementation; iron/zinc supplementation if deficient	Elimination diets: small effect in some children; omega-3: modest evidence; micronutrient supplementation: helpful only if genuinely deficient. Not first-line.

Management of comorbidities, e.g., ASD, ODD/CD, mood disorder, anxiety disorders ^[2]

This is a critical part of management that is often tested:

Comorbidity	Management Approach
ODD / CD	PMT is cornerstone; stimulants reduce oppositional behaviour secondary to ADHD; treatment of comorbid disorders, e.g., ADHD, depression ^[2]; if reactive aggression persists, atypical antipsychotics for reactive aggression (evidence is modest at best; only when poor emotional regulation occurs over prolonged ranges) ^[2]
Anxiety	Treat ADHD first (often anxiety improves when ADHD is treated); if persistent, add SSRI or CBT for anxiety; atomoxetine may be preferred (has anxiolytic properties)
Depression	Treat both concurrently; SSRIs for depression + stimulants for ADHD; monitor closely for suicidality
Tic disorder	Atomoxetine or alpha-2 agonists preferred over stimulants (clonidine treats both ADHD and tics); if stimulant is needed, monitor tics closely
ASD	Medications for ADHD symptoms (start lower, go slower — ASD children are more sensitive to side effects); address ASD-specific needs (social skills, communication, sensory issues) separately
Learning disorder	Identify through psychometric testing; provide specific remediation (e.g., specialist reading intervention for dyslexia); educational accommodations
Substance abuse	Non-stimulant preferred (atomoxetine); if stimulant needed, use long-acting formulations (lower abuse potential); concurrent substance abuse treatment

A "drug holiday" refers to intentionally stopping stimulant medication during periods when academic/functional demands are lower (e.g., school holidays, weekends).

Consideration	For Drug Holidays	Against Drug Holidays
Growth	Allows catch-up growth during off-medication periods
Side effects	Reduces cumulative side effect burden
Tolerance	May prevent pharmacological tolerance	Limited evidence for true tolerance
Social function		ADHD impairs social and family interactions — not just academic function; symptoms at home cause family strain
Safety		Impulsivity persists off medication → ↑ injury risk, especially in active play during holidays
Self-esteem		Continuous symptom control may be important for peer relationships and self-esteem

The decision should be individualised — some children benefit from drug holidays (especially those with significant appetite/growth concerns), while others function best with continuous treatment.

Parameter	Frequency	Purpose
Symptom review (rating scales from parents and teachers)	Every 1–3 months initially; then every 3–6 months	Assess treatment response; adjust dose
Height and weight	Every 3–6 months (plot on growth chart)	Detect growth deceleration from stimulants
Blood pressure and heart rate	Every visit for first 3 months; then every 3–6 months	Detect cardiovascular effects of stimulants
Side effect screen	Every visit	Appetite, sleep, mood, tics
Academic performance and social function	Every 3–6 months	Assess functional outcomes beyond symptoms
Comorbidity screen	Annual or when concerns arise	New-onset mood/anxiety disorders, substance use in adolescents
Medication review	Annually	Consider trial off medication to reassess need (especially in adolescence)

Treatment	Type	Effect Size	Key Indication	Key Contraindication / Caution
Methylphenidate (Ritalin/Concerta)	CNS stimulant	1.0	1st line for school-age and adults	Structural heart disease, phaeochromocytoma, psychosis, concurrent MAOIs
Lisdexamfetamine (Elvanse)	CNS stimulant (prodrug)	~1.0	1st line for adults (NICE); 2nd line for children	Same as methylphenidate
Atomoxetine (Strattera)	Non-stimulant (NRI)	0.7	FHx SA, tic disorder, stimulant-unresponsive ^[2]	Hepatic impairment, MAOIs, narrow-angle glaucoma
Clonidine	Alpha-2 agonist	0.3–0.5	Adjunct; comorbid tics; stimulant-induced insomnia	Abrupt cessation → rebound hypertension
Guanfacine (Intuniv)	Alpha-2A agonist	0.5–0.6	Monotherapy or adjunct; comorbid tics	Same as clonidine
PMT	Behavioural therapy	0.4–0.6	Most effective behavioural therapy ^[2]; 1st line for pre-school; adjunct at all ages	None
School accommodations	Educational	Variable	SEN under inclusion education policy ^[2]	None
CBT	Psychotherapy	0.3–0.5	Adolescents and adults; organisational skills, emotional regulation	Requires sufficient metacognitive maturity

High Yield Summary

Multimodal approach: ADHD management requires individualised combination of psychoeducation, behavioural therapy, medication, and school accommodations.
Age-based strategy: Pre-school → behavioural therapy first. School-age mild → watchful waiting + parent training. School-age moderate/severe → medication ± behavioural therapy. Adults → medication first-line.
Stimulants are first-line and the most effective treatment in all of psychiatry (effect size 1.0). Methylphenidate is the most commonly used. MoA: blocks DAT and NET → ↑ DA and NA in PFC → improved executive function.
Atomoxetine (NRI, effect size 0.7) is 2nd-line: preferred when there is family history of substance abuse, tic disorder, or stimulant intolerance. Takes 4–6 weeks to work. Rare hepatotoxicity (1/50,000).
Alpha-2 agonists (clonidine, guanfacine) are 3rd-line or adjunctive: useful for comorbid tics and stimulant-induced insomnia. Must taper — do not stop abruptly (rebound hypertension).
PMT is the most effective behavioural therapy: uses positive reinforcement, time-out, response cost, and behaviour modelling.
School accommodations are a right: ADHD is a SEN under HK inclusion education policy. Structured routines, token systems, daily report cards, and organisation skills teaching are key.
Monitor: Height, weight, BP, HR, side effects, and academic/social function at every visit. Annual medication review with consideration of trial off medication.
Comorbidities must be managed concurrently: ODD → PMT + stimulants; Anxiety → consider atomoxetine or add SSRI; Tics → atomoxetine or alpha-2 agonist preferred; SA risk → non-stimulant or long-acting formulation.
Stimulant side effects to know: ↓ appetite/weight, insomnia (avoid late dosing), growth deceleration, irritability/rebound, ↑ tics, ↑ HR/BP.

Active Recall - ADHD Management

References

^[2] Senior notes: ryanho-psych.md (Section 12.3 — Attention-deficit Hyperactivity Disorder: management approach, medications, non-pharmacological interventions; Section 12.4 — ODD/CD management including treatment of comorbid ADHD)

Complications of ADHD

Complications of ADHD can be understood at two levels: (1) complications of the disease itself (untreated or undertreated ADHD leading to cascading functional impairment) and (2) complications of treatment (adverse effects of pharmacotherapy). Both are commonly tested and clinically important.

The overarching concept: ADHD is not just "fidgeting and daydreaming." It is a chronic neurodevelopmental condition whose consequences compound over time. The executive dysfunction at its core — impaired inhibition, working memory, planning, and delay tolerance — ripples outward to affect every domain of life. Think of it as a pebble dropped in a pond: the initial neurobiological deficit sends waves through academics, social relationships, self-esteem, family dynamics, occupation, and physical safety, growing wider with each developmental stage.

1. Complications of Untreated / Undertreated ADHD

The notes explicitly organise functional impairment by developmental stage ^[2]:

Childhood: behavioural problems, academic problems, difficulties with social interactions, poor self-esteem ^[2]

Complication	Mechanism (From First Principles)	Details
Academic underachievement	Inattention → cannot sustain focus on instruction, reading, homework; impaired working memory → cannot hold multi-step instructions; impaired organisation → chaotic schoolwork; poor error monitoring → careless mistakes	ADHD children typically achieve 1–2 grade levels below their intellectual potential. This is NOT because they lack intelligence — it is because the "delivery system" (executive function) that translates ability into performance is impaired. Learning disorders occur with undue frequency ^[2] — when ADHD + LD co-exist, the academic impact is multiplicative.
Behavioural problems	Motor disinhibition → disruptive behaviour in class; impulsivity → rule-breaking without malicious intent; low frustration tolerance → anger outbursts	Teachers may interpret the child as "naughty" or "defiant," but the behaviour stems from impulsive flouting of social rules ^[2] rather than deliberate opposition (cf. ODD). Frequent reprimands and punishment → learned helplessness and resentment.
Social difficulties and peer rejection	Impulsivity → interrupts, intrudes, cannot take turns; hyperactivity → perceived as "annoying"; inattention → misses social cues, doesn't follow conversation flow; disinhibition in social relationships ^[2] → acts overly familiar	ADHD children are among the most socially rejected in the classroom. Peer rejection is one of the strongest predictors of poor long-term outcome. The tragedy: these children want to have friends but their executive dysfunction sabotages social interactions.
Poor self-esteem	Chronic academic failure + social rejection + frequent criticism from adults and peers → the child internalises a narrative of "I am stupid / bad / broken"	By school-age, many ADHD children have already developed significant self-esteem difficulties. This becomes a risk factor for later depression and anxiety.
Injuries	Recklessness in dangerous situations ^[2] → crosses roads without looking, climbs to dangerous heights, impulsive physical play; impaired risk assessment (vmPFC dysfunction)	ADHD children have 2–3 times the rate of emergency department visits and accidental injuries compared to non-ADHD peers. This includes fractures, head injuries, burns, and poisoning.

Adolescence: above issues, legal issues, relationship problems, injuries ^[2]

Complication	Mechanism	Details
School dropout / academic failure	Cumulative academic deficit from childhood + increasing cognitive demands in secondary school + worsening organisational burden (multiple subjects, teachers, deadlines)	Without treatment, ADHD adolescents are at significantly higher risk of repeating a grade, being suspended, or dropping out of school entirely.
Legal issues	Impulsive decision making and recklessness (e.g., substance abuse, joining of triad) ^[2]; decision-making favouring immediate gratification over delayed consequences ^[2]	The mesolimbic "reward pathway" dysfunction means these adolescents are particularly drawn to immediately rewarding but risky behaviours. Impulsivity → shoplifting, vandalism, fighting. When comorbid with CD, particularly at risk of antisocial, criminal behaviours ^[2].
Relationship problems	Impulsivity → says hurtful things without thinking; inattention → appears not to care or listen; emotional dysregulation → anger outbursts; poor social skills from childhood carry forward	Difficulty maintaining friendships and romantic relationships; social isolation.
Substance use initiation	Impulsivity + sensation-seeking + peer influence + self-medication hypothesis (substances temporarily relieve executive dysfunction or emotional distress)	ADHD adolescents are at ~2× risk of initiating substance use and ~1.5× risk of developing substance use disorders compared to non-ADHD peers. SA (~15%) comorbidity ^[2]. Importantly, treatment with stimulants appears to be protective against later substance abuse — not causative (the "gateway drug" myth is unfounded).
Reckless driving	Impulsivity → speeding, tailgating, running red lights; inattention → misses road signs, distracted driving; delay aversion → impatience with traffic	Adolescents and young adults with ADHD have 2–4 times the rate of motor vehicle accidents, traffic violations, and licence suspensions compared to controls.
Injuries/accidents	Same impulsivity and risk-taking as in childhood, amplified by access to cars, extreme sports, and reduced parental supervision ^[2]	The injury profile shifts from playground accidents to motor vehicle accidents, sports injuries, and alcohol/substance-related injuries.

Adulthood: occupational failure, self-esteem issues, relationship problems, SA, injuries/accidents ^[2]

Complication	Mechanism	Details
Occupational failure	Paralyzing procrastination; slowness, inefficiency; poor time management; disorganisation ^[2] → chronic underperformance; impulsivity → quitting jobs ^[2] impulsively; inattention → errors, missed deadlines; emotional dysregulation → conflicts with colleagues/supervisors	Adults with ADHD have lower educational attainment, lower income, higher rates of unemployment, and more frequent job changes than matched peers. They are often "underachievers" relative to their intellectual potential. Workaholic, overscheduled and overwhelmed ^[2] — some adults compensate by overcommitting, leading to burnout.
Self-esteem issues	Decades of underachievement, criticism, and failed relationships → deeply ingrained negative self-concept ^[2]	Many adults with undiagnosed ADHD describe a lifelong sense of "not living up to my potential" — when finally diagnosed, they often experience both relief ("It's not my fault") and grief ("What could I have been?").
Relationship problems	Inattention → partner feels ignored; impulsivity → losing temper, ending relationships ^[2]; poor listening → communication breakdown; emotional dysregulation → volatile arguments; constant activity leading to family tension ^[2]	ADHD adults have higher rates of marital discord, separation, and divorce. The non-ADHD partner often becomes the "manager" of the household, leading to resentment and power imbalance.
Substance abuse (SA)	Impulsivity + sensation-seeking; self-medication (alcohol/cannabis to "slow down," stimulants to focus); addictive personality ^[2]; genetic overlap between ADHD and SA	~15–25% of adults with ADHD have comorbid substance use disorders (higher than general population). Alcohol, cannabis, and nicotine are most common. When hyperkinesis was present in childhood but has disappeared and been succeeded by another condition, such as dissocial personality disorder or substance abuse, the current condition rather than the earlier one is coded ^[2].
Injuries/accidents	Driving too fast ^[2]; impulsive risk-taking; inattention to hazards	Adults with ADHD have more traffic accidents, workplace injuries, and sports injuries.
Mood disorders (depression, anxiety)	Secondary to chronic failure, rejection, and criticism; shared genetic vulnerability; neurobiological overlap (catecholamine dysfunction)	~20% comorbid mood disorder ^[2]; ~25% comorbid anxiety ^[2]. Depression in ADHD adults is often of the "demoralisation" type — reactive to life circumstances rather than endogenous.

The ADHD Cascade — Why Early Treatment Matters

ADHD complications are cumulative and progressive. Academic failure in childhood → low self-esteem → school dropout in adolescence → substance use → occupational failure in adulthood → relationship breakdown → depression. Each untreated year adds another link to this chain. This is why early identification and treatment is so important — not just for symptom control, but to prevent this cascade of secondary complications.

Poor prognostic factors: learning difficulties, antisocial behaviour, severe overactivity ^[2]

In particular, when comorbid with CD, particularly at risk of antisocial, criminal behaviours and SA ^[2]

This deserves special emphasis because it represents the worst-case trajectory:

The ODD → CD → Antisocial PD pathway is one of the most well-established developmental trajectories in child psychiatry. ADHD acts as an accelerant on this pathway — the impulsivity, disinhibition, and executive dysfunction of ADHD amplify the antisocial tendencies of CD. Prognosis is worse for early-onset cases (antisocial behaviour in 40% early-onset cases and only 20% in adolescent-onset cases) ^[2].

2. Complications of Treatment

Side effects: irritability, depression, insomnia, poor appetite (with ↓ height/weight growth), ↑ tic disorders ^[2]

Complication	Mechanism	Clinical Significance	Management
↓ Appetite and weight loss	DA agonism in hypothalamic appetite centres → central appetite suppression ^[2]	Most common reason for parental concern; can lead to malnutrition in severe cases	Calorie-dense meals when medication has worn off; drug holidays for catch-up; consider formulation change
Growth deceleration	Combination of ↓ caloric intake + possible direct suppression of GH secretion (uncertain) ^[2]	Average final height reduction ~1–3 cm (clinically modest but parents worry); most evidence suggests catch-up occurs after discontinuation	Monitor height/weight every 3–6 months on growth chart; drug holidays during school vacations; reassure parents that final adult height is minimally affected
Insomnia	Stimulant effect on ascending reticular activating system; enhanced DA/NA in wake-promoting circuits persists into evening ^[2]	Sleep deprivation worsens next-day ADHD symptoms → vicious cycle	Avoid dosing after 5pm in primary school and 6pm in secondary school ^[2]; switch to shorter-acting formulation; add low-dose melatonin for sleep onset
Irritability / mood swings	"Rebound effect" — as medication wears off, there is an acute drop in catecholamines below baseline → transient worsening of ADHD symptoms + irritability ^[2]	Can mimic comorbid mood disorder; may cause family distress in the evening	Overlap doses; switch to longer-acting formulation to smooth the pharmacokinetic curve; dose reduction if overstimulated
Depression	Can occur as a direct pharmacological effect (rare); more commonly as rebound phenomenon or demoralisation when medication wears off ^[2]	Must distinguish from comorbid MDD	If persistent, consider dose reduction, formulation change, or switch to atomoxetine; screen for comorbid depression
↑ Tic disorders	DA agonism in the basal ganglia may unmask latent tic vulnerability or exacerbate pre-existing tics ^[2]	Controversial — some studies show stimulants do NOT worsen tics overall, but individual patients can be affected	Monitor; if tics emerge/worsen, consider reducing dose, switching to atomoxetine, or adding alpha-2 agonist (clonidine/guanfacine treat both ADHD and tics)
Tachycardia	Peripheral sympathomimetic effect (NA release at cardiac sympathetic nerve terminals → ↑ HR) ^[2]	Rarely clinically significant in healthy children; becomes concerning in those with pre-existing cardiac conditions	Monitor HR/BP at each visit; ECG if symptomatic; contraindicated in structural heart disease
Cardiovascular events (rare)	Sympathomimetic effects → ↑ HR, ↑ BP; in patients with undetected structural heart disease or arrhythmias, this can (very rarely) precipitate sudden cardiac death	Extremely rare (~1/million patient-years); risk comparable to general paediatric population	Pre-treatment cardiac screening (history, exam, ± ECG); avoid in structural heart disease, cardiomyopathy, serious arrhythmias
Abuse / diversion potential	Stimulants enhance DA in the mesolimbic reward circuit → euphorigenic at supratherapeutic doses; tablets can be crushed and snorted/injected	Primarily a concern in adolescents and adults; family members or peers may seek to obtain the medication	Use long-acting formulations (harder to abuse); lisdexamfetamine (prodrug, cannot be effectively snorted/injected); non-stimulant alternatives if high risk; monitor prescription use
Psychosis (rare)	Excessive DA agonism at supratherapeutic doses → positive psychotic symptoms (hallucinations, paranoia); very rare at therapeutic doses	Important to recognise; reversible on discontinuation	Discontinue stimulant; evaluate for underlying psychotic disorder; consider non-stimulant alternatives

Side effects: nausea, abdominal pain, LOA, sleep disturbances, deranged LFT, severe liver damage (1/50k) ^[2]

Complication	Mechanism	Clinical Significance
Epigastric discomfort, nausea/vomiting	Direct GI irritation + central NA effects on the chemoreceptor trigger zone ^[2]	Most common side effects; usually transient; take with food to minimise
Sedation	NA modulation of arousal circuits ^[2]	Can be beneficial if given at night (helps with insomnia); problematic if given in the morning
Decreased appetite	Similar to stimulants but generally less severe ^[2]	Monitor weight; less growth concern than stimulants
Mood swings / irritability	Central catecholaminergic effects ^[2]	Monitor; rare suicidal ideation (FDA black box warning) — counsel families to report changes in mood or behaviour
Deranged LFTs / hepatotoxicity	Idiosyncratic hepatocellular injury (not dose-dependent) → mechanism unclear, possibly immune-mediated ^[2]	Severe liver damage: 1/50,000 ^[2] — rare but potentially fatal. Counsel families about warning signs: jaundice, dark urine, abdominal pain, pruritus. Baseline LFTs recommended.
Suicidal ideation	FDA black box warning; mechanism uncertain — possibly related to acute NA changes during initiation affecting mood regulation	~0.4% vs 0% placebo in trials; monitor closely in first months of treatment, especially in patients with comorbid depression

Complication	Mechanism	Clinical Significance
Sedation	Central α₂-agonism → ↓ locus coeruleus firing → ↓ arousal	Most common side effect; usually transient (improves over 2–4 weeks); can be useful if given at night for stimulant-induced insomnia
Hypotension and bradycardia	α₂-agonism → ↓ sympathetic outflow → ↓ peripheral vascular resistance and ↓ HR	Monitor BP/HR; avoid in patients on other hypotensive agents
Rebound hypertension	Abrupt cessation → upregulated sympathetic nervous system (α₂-receptors have been downregulated during chronic use) → unopposed sympathetic tone	Must taper gradually — never stop abruptly. Educate families about this risk.
Dry mouth	↓ Sympathetic stimulation of salivary glands	Usually mild and transient

These are often under-appreciated but profoundly impactful:

Domain	Complication	Explanation
Family	Parental stress, marital conflict, sibling resentment	Managing an ADHD child is exhausting; parents disagree on discipline; siblings feel neglected as the ADHD child demands disproportionate attention. Parents of ADHD children have higher rates of depression and anxiety themselves.
Financial	Cost of treatment, tutoring, special education, lost parental income	In Hong Kong, specialist consultations, medications, educational psychology assessments, and tutoring create significant financial burden.
Stigma	Social stigma around ADHD diagnosis and medication use	In Chinese culture, there may be particular stigma around psychiatric diagnoses in children; some parents resist diagnosis or medication due to fear of "labelling" their child. This can delay treatment and worsen outcomes.
Educational system	Strain on teachers, disruption to classrooms	Without adequate SEN support, ADHD children are frequently punished, excluded, or moved between schools — all of which worsen outcomes.

Course: generally show age-dependent ↓ severity (hyperactivity > impulsiveness > inattention), but substantial proportion persist into adulthood or experience functional impairment ^[2]

~50% retain full diagnostic criteria in adolescence ^[2]

~40–60% experience problems in adulthood ^[2]

Long-Term Outcome	Prevalence	Key Factors
Full remission by adulthood	~20–35%	Earlier diagnosis and treatment, absence of comorbidities, supportive environment, predominantly hyperactive presentation (most likely to remit)
Partial remission (symptoms below threshold but functional impairment persists)	~30–40%	Residual inattention causing occupational and relationship difficulties; may not meet full criteria but still impaired
Full persistence into adulthood	~15–30%	Severe childhood ADHD, comorbid CD or mood disorders, learning difficulties, family adversity
Succession by another disorder	Variable	When hyperkinesis was present in childhood but has disappeared and been succeeded by another condition, such as dissocial personality disorder or substance abuse, the current condition rather than the earlier one is coded ^[2]

High Yield Summary

ADHD complications are cumulative and progressive: Academic failure → low self-esteem → social rejection → substance use → occupational failure → relationship breakdown → depression. Early treatment interrupts this cascade.
Childhood complications: Academic underachievement, behavioural problems, peer rejection, poor self-esteem, injuries from recklessness.
Adolescent complications: School dropout, legal issues (especially with comorbid CD), substance use initiation, reckless driving, relationship problems, injuries.
Adult complications: Occupational failure, chronic self-esteem issues, relationship instability, substance abuse, mood disorders, injuries/accidents.
Worst trajectory: ADHD + ODD → CD → Antisocial Personality Disorder + substance abuse + criminality. Comorbid CD is the strongest poor prognostic factor.
Stimulant complications: ↓ appetite/weight, growth deceleration, insomnia, irritability/rebound, ↑ tics, tachycardia, rare psychosis, abuse potential. Avoid dosing after 5–6pm.
Atomoxetine complications: GI upset, sedation, mood changes, rare hepatotoxicity (1/50,000), suicidal ideation (FDA black box warning).
Alpha-2 agonist complications: Sedation, hypotension, bradycardia, rebound hypertension if stopped abruptly — always taper.
Psychosocial burden: Family stress, financial cost, stigma (particularly relevant in HK Chinese culture), educational system strain.
Prognosis: ~50% retain criteria in adolescence; ~40–60% have adult problems; remission is most likely for hyperactivity, least likely for inattention.

Active Recall - ADHD Complications

References

^[2] Senior notes: ryanho-psych.md (Section 12.3 — Attention-deficit Hyperactivity Disorder: clinical features and functional impairment, course and prognosis, medications and side effects; Section 12.4 — ODD/CD course and prognosis)

High Yield Summary

Definition: ADHD is a neurodevelopmental disorder of inattention ± hyperactivity-impulsivity, pervasive across settings, with early onset (< 12y DSM-5, < 6y ICD-10), causing functional impairment.
Epidemiology: 2nd commonest childhood psychiatric disorder; M > F (3:1); prevalence ~5–7% in children; ~50% comorbid with other disorders (ODD ~40%, CD ~20%, learning disorders ~25%, anxiety ~25%, mood ~20%).
Pathophysiology: Hypoactive dopamine and noradrenaline in fronto-striatal and mesolimbic circuits → executive dysfunction (poor inhibition, working memory, attention) + delay aversion.
Genetics: Heritability ~70–80%; polygenic; involves dopamine and serotonin system genes.
Neuroimaging: ↓ Volume in basal ganglia and PFC; delayed cortical maturation; disrupted fronto-striatal connectivity.
Three symptom domains: Inattention (presents later, most persistent), Hyperactivity (presents first, improves most with age), Impulsivity (intermediate trajectory).
Lifespan: Hyperactivity > impulsivity > inattention in age-dependent improvement; ~50% retain criteria in adolescence; ~40–60% have adult functional impairment.
ICD-10 vs DSM-5: ICD-10 (Hyperkinetic Disorder, F90) requires BOTH inattention + hyperactivity; DSM-5 allows EITHER domain; ICD-11 has aligned with DSM-5.
Key comorbidity to remember: ADHD + CD = worst prognosis (antisocial trajectory, substance abuse, criminality).
Adult ADHD: Presents differently — internalised restlessness, procrastination, poor time management, relationship instability, low frustration tolerance.

High Yield Summary

ADHD symptoms are non-specific — inattention, hyperactivity, and impulsivity appear in many conditions. Always consider the differential systematically.
The 3 golden rules for ADHD diagnosis over mimics: (a) Pervasive across ≥ 2 settings, (b) Early onset (before age 12), (c) Chronic/trait-like (not episodic).
ADHD vs ODD: "Can't do it" (executive dysfunction) vs "Won't do it" (defiance). Co-occur in ~40%.
ADHD vs Anxiety: Distracted by external stimuli (ADHD) vs internal worries (anxiety).
ADHD vs Depression: Lifelong since childhood (ADHD) vs later onset and episodic (depression). Both impair concentration but via different mechanisms.
ADHD vs Mania: Chronic trait-like course (ADHD) vs episodic with elated mood, grandiosity, ↓ need for sleep, flight of ideas (mania). ADHD should NOT have grandiosity or ↓ need for sleep.
ADHD vs ASD: Wants to socialise but fails due to impulsivity (ADHD) vs fundamental deficit in social reciprocity (ASD). Can co-occur.
ADHD vs Learning Disorder/ID/Gifted: Symptoms only during academic tasks (learning disorder) vs pervasive (ADHD).
ADHD vs Substance Abuse: Symptoms only in context of substance use (SA) vs lifelong (ADHD). Both can co-exist.
Always exclude medical causes: Thyroid, sleep disorders, sensory impairment, seizures, lead exposure.

High Yield Summary

ADHD is a clinical diagnosis — no single test confirms it. Diagnosis requires integration of clinical interview, collateral history from multiple informants, rating scales, developmental history, and exclusion of differential diagnoses.
DSM-5 Criteria: ≥ 6/9 symptoms (≥ 5 if age ≥ 17) in inattention and/or hyperactivity-impulsivity; ≥ 6 months duration; onset before age 12; present in ≥ 2 settings; functional impairment; not better explained by another disorder.
ICD-10 (Hyperkinetic Disorder): Stricter — requires BOTH inattention AND hyperactivity; onset before age 6. ICD-11 has aligned with DSM-5.
Rating scales (Conners, SNAP-IV, SDQ): Supportive but NOT diagnostic on their own. Need parent AND teacher versions to confirm pervasiveness.
Investigations are to exclude mimics and establish pre-treatment baselines: TFTs (thyroid), FBC + iron (deficiency → ↓ dopamine), lead level, audiometry/vision, ECG (pre-stimulant).
Neuropsychological testing: Not routine. Useful for ambiguous cases, comorbid learning disorders, educational accommodations. Classic ADHD profile: low working memory + processing speed indices relative to full-scale IQ.
Pre-treatment baselines: Height, weight, BP, HR, ECG (if cardiac risk factors), LFTs (if starting atomoxetine).
Multiple informant approach: ALWAYS get information from parents AND teachers — you need to confirm pervasiveness across settings.
Adult ADHD: Requires retrospective confirmation of childhood onset; threshold lowered to ≥ 5 symptoms for age ≥ 17; use DIVA or ASRS for structured assessment.
Key difference between ICD-10 and DSM-5: ICD-10 requires both domains + onset < 6y (stricter); DSM-5 allows either domain + onset < 12y (broader). ICD-11 now aligns with DSM-5.

High Yield Summary

Multimodal approach: ADHD management requires individualised combination of psychoeducation, behavioural therapy, medication, and school accommodations.
Age-based strategy: Pre-school → behavioural therapy first. School-age mild → watchful waiting + parent training. School-age moderate/severe → medication ± behavioural therapy. Adults → medication first-line.
Stimulants are first-line and the most effective treatment in all of psychiatry (effect size 1.0). Methylphenidate is the most commonly used. MoA: blocks DAT and NET → ↑ DA and NA in PFC → improved executive function.
Atomoxetine (NRI, effect size 0.7) is 2nd-line: preferred when there is family history of substance abuse, tic disorder, or stimulant intolerance. Takes 4–6 weeks to work. Rare hepatotoxicity (1/50,000).
Alpha-2 agonists (clonidine, guanfacine) are 3rd-line or adjunctive: useful for comorbid tics and stimulant-induced insomnia. Must taper — do not stop abruptly (rebound hypertension).
PMT is the most effective behavioural therapy: uses positive reinforcement, time-out, response cost, and behaviour modelling.
School accommodations are a right: ADHD is a SEN under HK inclusion education policy. Structured routines, token systems, daily report cards, and organisation skills teaching are key.
Monitor: Height, weight, BP, HR, side effects, and academic/social function at every visit. Annual medication review with consideration of trial off medication.
Comorbidities must be managed concurrently: ODD → PMT + stimulants; Anxiety → consider atomoxetine or add SSRI; Tics → atomoxetine or alpha-2 agonist preferred; SA risk → non-stimulant or long-acting formulation.
Stimulant side effects to know: ↓ appetite/weight, insomnia (avoid late dosing), growth deceleration, irritability/rebound, ↑ tics, ↑ HR/BP.

High Yield Summary

ADHD complications are cumulative and progressive: Academic failure → low self-esteem → social rejection → substance use → occupational failure → relationship breakdown → depression. Early treatment interrupts this cascade.
Childhood complications: Academic underachievement, behavioural problems, peer rejection, poor self-esteem, injuries from recklessness.
Adolescent complications: School dropout, legal issues (especially with comorbid CD), substance use initiation, reckless driving, relationship problems, injuries.
Adult complications: Occupational failure, chronic self-esteem issues, relationship instability, substance abuse, mood disorders, injuries/accidents.
Worst trajectory: ADHD + ODD → CD → Antisocial Personality Disorder + substance abuse + criminality. Comorbid CD is the strongest poor prognostic factor.
Stimulant complications: ↓ appetite/weight, growth deceleration, insomnia, irritability/rebound, ↑ tics, tachycardia, rare psychosis, abuse potential. Avoid dosing after 5–6pm.
Atomoxetine complications: GI upset, sedation, mood changes, rare hepatotoxicity (1/50,000), suicidal ideation (FDA black box warning).
Alpha-2 agonist complications: Sedation, hypotension, bradycardia, rebound hypertension if stopped abruptly — always taper.
Psychosocial burden: Family stress, financial cost, stigma (particularly relevant in HK Chinese culture), educational system strain.
Prognosis: ~50% retain criteria in adolescence; ~40–60% have adult problems; remission is most likely for hyperactivity, least likely for inattention.

Attention-deficit Hyperactivity Disorder

References

1. Definition

2. Epidemiology

2.1 Prevalence

2.2 Demographics

2.3 Comorbidities

3. Risk Factors

3.1 Biological / Genetic Factors

3.2 Neurobiological Factors

3.3 Psychological Factors

3.4 Social / Environmental Factors

4. Anatomy and Neurobiological Basis

4.1 Key Brain Regions

4.2 Key Circuits

4.3 Neurotransmitters

5. Classification

5.1 DSM-5 Presentations (Specifiers)

5.2 ICD-10 Classification (Hyperkinetic Disorder, F90)

5.3 ICD-11 Update

5.4 DSM-5 Severity Specifiers

6. Clinical Features

6.1 Symptoms — Inattention Domain

6.2 Symptoms — Hyperactivity Domain

6.3 Symptoms — Impulsivity Domain

6.4 Associated Features and Signs

6.5 Clinical Features by Developmental Stage

Pre-school (ages 3–5)

School-age (ages 6–12) — the "classic" presentation

Adolescence

Adulthood

6.6 Course and Prognosis

6.7 Functional Impairment

7. Summary of Etiology and Pathophysiology — Integrated Model

Active Recall - ADHD Definition, Epidemiology, Aetiology & Clinical Features

References

Differential Diagnosis of ADHD

Differential Diagnosis Table

Overlap Summary Table

Diagnostic Decision-Making Algorithm

Key Differentiating Principles — Organised by the "Why"

Approach to the Differential — What to Assess Clinically

Active Recall - ADHD Differential Diagnosis

References

Diagnostic Criteria

Why Is the Diagnosis Clinical?

DSM-5 Diagnostic Criteria (Attention-Deficit/Hyperactivity Disorder)

Criterion A — Symptom Domains

Domain 1: Inattention (9 items)

Domain 2: Hyperactivity and Impulsivity (9 items)

Criterion B — Age of Onset

Criterion C — Pervasiveness

Criterion D — Functional Impairment

Criterion E — Exclusion

Specifiers

ICD-10 Diagnostic Criteria (Hyperkinetic Disorder, F90)

ICD-11 Update (6A05 — Attention Deficit Hyperactivity Disorder)

Adult ADHD — Diagnostic Considerations

Diagnostic Algorithm

Step-by-Step Clinical Assessment Pathway

Step 1: Suspicion / Referral

Step 2: Triage by Severity

Step 3: Comprehensive Specialist Assessment

Detailed Assessment Components

A. Clinical Interview

B. Standardised Rating Scales

C. Developmental and Family History

D. Physical Examination

Investigation Modalities

Principle: ADHD Is a Clinical Diagnosis — Investigations Serve Specific Purposes

Investigation Table

Neuropsychological Testing

Pre-Treatment Baseline Investigations

Summary: What Makes the Diagnosis

Active Recall - ADHD Diagnostic Criteria, Algorithm & Investigations

References

Management of ADHD

Guiding Principles

Management Algorithm

Stepwise Approach by Severity and Age