Classification attempts to bring some order into the great diversity of phenomena encountered in clinical practice. ^[1]

Think of it this way: if every clinician described depression in their own words, no two psychiatrists could agree on who has it, what to prescribe, or what outcome to expect. Classification solves this by creating shared diagnostic categories.

"To identify groups of patients who share similar clinical features, so that suitable treatment can be planned and the likely outcome predicted." ^[1]

"Able to develop a standardized approach in diagnosis." ^[1]

Additional reasons from the PSY01 introductory lecture and supporting notes ^[2][3]:

• Facilitates communication between patients, professionals, and researchers
• Enables epidemiological research (you can't study prevalence if you can't define the condition)
• Supports training and education
• Guides medico-legal decisions (e.g., fitness to plead, involuntary admission criteria)

Hallucination, delusion, disorganized speech, catatonia

These examples are phenomena that require precise description before diagnostic attribution. Hallucinations and delusions may occur in primary psychotic disorders, mood disorders, delirium, neurological or other medical illness, and substance/medication-related states. Culture, sleep-wake transitions and context also matter; the presence of one phenomenon does not by itself diagnose schizophrenia.

Depressed mood, worries, checking, recall of fearful or traumatic events Symptoms are excessive, irrational, and uncontrollable

Sadness, worry, checking and trauma memories all occur outside disorder. The slide's phrase "excessive, irrational and uncontrollable" is a useful contrast but not a universal test: assess persistence, context, proportionality, control, distress, functional impact and the specific criteria. Do not tell a depressed or traumatised person that their experience is simply "irrational."

Impaired cognitive functioning — e.g., cognitive decline in dementia Impaired social functioning — e.g., deficits in social-emotional reciprocity in ASD Impaired attention — e.g., ADHD

Here the problem is not an abnormal experience per se, but a deficit in a normally developed capacity.

Impaired sleep (insomnia, hypersomnia, parasomnia, circadian rhythm disorders) Impaired sexual and gender function (erectile disorder, gender dysphoria, paraphilia) Impaired eating (eating disorders) Impaired experience of pain and other somatic symptoms Impaired elimination (enuresis)

These examples involve basic functions or embodied experience, but the slide's grouping is only a teaching scaffold. Gender dysphoria should not be described as an "impaired gender function", and a paraphilic interest is not automatically a paraphilic disorder; diagnosis depends on the relevant criteria, distress/impairment and/or harm or risk to others.

Addiction, including non-substance (e.g., gambling) Impulse-control presentations (the slide gives trichotillomania)

The person has difficulty controlling a behaviour despite adverse consequences. Taxonomy caution: DSM-5/DSM-5-TR places trichotillomania under obsessive-compulsive and related disorders, not the disruptive/impulse-control chapter. Gambling disorder is classified with substance-related and addictive disorders.

Personality disorders

These represent enduring, pervasive patterns of inner experience and behaviour that deviate markedly from cultural expectations, are inflexible, and lead to distress or impairment.

These properties can conflict: a very simple rule may be reliable but invalid, while a nuanced formulation may be more faithful to the person but harder to standardise. Reliability is necessary for a useful classification, not proof that its categories are biologically discrete.

Ideally, there should be qualitative difference in biological underpinnings between diagnoses, but limited evidence is available that different disorders have distinct genetic factors, neurophysiology, neuropathology, and neuroimaging findings.

This is a critical concept. In cardiology, an MI has a clear biological marker (troponin rise + ECG changes + wall motion abnormality). In psychiatry, we have no equivalent. The current system relies on:

• Self-report of psychiatric symptoms — inherently subjective
• Distress or impairment in functioning — the symptoms must matter clinically
• Diagnostic overlap and heterogeneity remain common. Schizoaffective disorder is not simply "both symptom groups at once"; its diagnosis depends on the longitudinal relationship between mood episodes and psychosis.

Clearer criteria result in higher reliability

Examples from the lecture:

• "Pervasive low mood" is more reliable than "low mood" (adds a qualifier)
• "Poor sleep at least 3 times per week" is more reliable than "poor sleep" (adds a frequency threshold)

The lesson: operationalize your criteria — make them measurable and quantifiable.

Begin with open-ended questions in history taking

• Example: "How is your sleep in the past week?" Follow with focused questions when needed
• Example: after the narrative, clarify sleep onset, awakenings, total sleep, opportunity and daytime impact Ask patients to elaborate Focus on one symptom at a time

Why begin open? It lets the patient describe experience in their own language and reduces premature framing. Closed questions are not inherently bad: they are useful for clarifying frequency, duration, risk and specific criteria after the narrative. Avoid leading, compound and accusatory wording.

Every symptom should be characterized along these dimensions:

Screening tools — not for diagnosis, only for screening

Why the distinction matters: A positive screen means the patient needs further clinical assessment. It does not establish diagnosis, cause, severity of risk or treatment need by itself. Conversely, a low total score never overrides a concerning clinical history or response to a safety item.

Schizophrenia Spectrum and Other Psychotic Disorders:

Diagnostic Criteria for Schizophrenia (DSM-5/DSM-5-TR):

Criterion A — Characteristic Symptoms: 2 or more of the following, each present for a significant portion of time during a 1-month period:

1. Delusions
2. Hallucinations
3. Disorganized speech (e.g., frequent derailment or incoherence)
4. Grossly disorganized or catatonic behaviour
5. Negative symptoms (affective flattening, alogia, avolition)

At least one of the two or more symptoms must be delusions, hallucinations or disorganised speech. The slide's list is visually complete but omits this discriminator.

Criterion B — Social/occupational dysfunction: one or more major areas of functioning markedly below the level achieved prior to onset

Criterion C — Duration: Continuous signs of the disturbance persist for at least 6 months. This 6-month period must include at least 1 month of symptoms (Criterion A). May include periods of prodromal or residual symptoms.

Further exclusions — schizoaffective and bipolar/depressive disorders with psychotic features; substance/medication or another medical condition; and, where autism spectrum disorder or a childhood communication disorder is present, schizophrenia is added only when prominent delusions or hallucinations also meet the required duration.

Clinical Vignette from the Lecture — "Mr. Tung" ^[1]:

68-year-old divorced man, 6 weeks of voices discussing him and reading his thoughts aloud, referential/persecutory interpretations of people and media, disorganised speech, poor self-care and negative symptoms. This is his eighth episode over a 30-year illness, with marked occupational and relationship decline and poor insight.

This vignette illustrates:

• Multiple Criterion A symptoms (hallucinations, disorganized speech, negative symptoms)
• Functional decline (Criterion B) — former university student → unemployed, divorced
• The current exacerbation is only 6 weeks, but the longitudinal 30-year course establishes duration; never diagnose from the latest episode alone
• Chronic, relapsing course with poor insight and treatment non-adherence

Characteristic Symptoms: 5 or more during the same 2-week period; at least one must be (1) depressed mood or (2) loss of interest/pleasure:

Mnemonic: SIG E CAPS (Sleep, Interest, Guilt, Energy, Concentration, Appetite, Psychomotor, Suicidality) — plus depressed mood.

Additional criteria:

• Clinically significant distress or impairment
• Not attributable to a substance or another medical condition
• Establish whether there has ever been a manic or hypomanic episode; if so, reconsider unipolar MDD and assess the bipolar spectrum

A distinct period of elevated, expansive or irritable mood AND persistently increased activity or energy, lasting at least 1 week and present most of the day nearly every day (or any duration if hospitalisation is necessary), plus 3 or more symptoms — 4 if mood is only irritable:

The disturbance must cause marked social or occupational impairment, require hospitalisation to prevent harm, or include psychotic features, and it must not be attributable to a substance or another medical condition. This distinguishes mania from hypomania as well as from ordinary high energy.

Mood Disorders Classification from the lecture:

Depressive disorders: single/recurrent episodes, dysthymia, PMDD Bipolar disorders: episodic pathological elevation/irritability and energy; depressive episodes are common but their diagnostic role differs by subtype

• Mania usually lasts ≥ 1 week unless hospitalisation is needed; hypomania lasts ≥ 4 consecutive days; "mixed episode" has been replaced by mixed-features specifiers
• Depressive episodes can last for weeks or months
• Inter-episode recovery varies; residual symptoms and functional impairment can persist
• Subtypes: Bipolar I, Bipolar II, Cyclothymia

A. Excessive anxiety and worry occurring more days than not for at least 6 months, about a number of events or activities B. Difficult to control the worry C. 3 or more of:

D. Clinically significant distress or impairment E. Not attributable to a substance or another medical condition, and not better explained by another mental disorder

For adults, at least 3 of the 6 associated symptoms are required; for children, only 1 is required. The worry must be difficult to control and span a number of domains rather than being confined to the focus of another disorder.

A panic attack is an abrupt surge of intense fear or discomfort that reaches a peak within minutes, with 4 or more of the following:

For panic disorder: recurrent unexpected panic attacks, with at least one attack followed by ≥ 1 month of persistent concern/worry about further attacks or their consequences, and/or maladaptive behavioural change related to the attacks.

Key distinction: The 1-month rule applies to what follows an attack, not to attacks occurring continuously for a month. Panic attacks are a specifier that can occur across disorders; panic disorder requires recurrent unexpected attacks plus the aftermath criterion and substance/medical/other-disorder exclusions. If attacks are exclusively cued by social scrutiny, for example, consider social anxiety disorder rather than automatically adding panic disorder.

Generalized anxiety disorder, Panic disorder, Agoraphobia, Social phobia, Specific phobia, Separation anxiety disorder, Selective mutism, Anxiety disorder substance-induced/another medical condition, OS/US Anxiety disorder

Anorexia nervosa, Bulimia nervosa, Binge-eating disorder, Pica, Rumination disorder, Avoidant/restrictive food intake disorder, OS/US

Diagnostic Criteria for Anorexia Nervosa:

A. Restriction of energy intake → significantly low body weight B. Intense fear of gaining weight OR persistent behaviour interfering with weight gain C. Disturbance in body image / undue influence of weight on self-evaluation / lack of recognition of seriousness D. Current subtype: restricting vs binge-eating/purging, based on behaviour during the last 3 months

Insomnia disorder, Parasomnias, Hypersomnolence/Narcolepsy, Circadian rhythm disorders, Breathing-related sleep disorders (e.g., OSAS), Restless leg syndrome/PLMD

Diagnostic Criteria for Insomnia Disorder:

A. Dissatisfaction with sleep quantity or quality: difficulty initiating, maintaining, or early morning awakening B. Clinically significant distress or impairment C. At least 3 nights per week for at least 3 months D. Despite adequate opportunity for sleep E. Not better explained by another sleep-wake disorder and not attributable to a substance; coexisting mental or medical disorders do not exclude insomnia when the sleep complaint warrants independent clinical attention The older primary/secondary distinction has been replaced by insomnia disorder with relevant comorbidities documented

A. Persistent deficits in social communication and social interaction across multiple contexts:

• Deficits in social-emotional reciprocity (e.g., failure of normal back-and-forth conversation)
• Deficits in nonverbal communicative behaviours (e.g., abnormal eye contact and body language)
• Deficits in developing, maintaining, and understanding relationships (e.g., absence of interest in peers)

B. Restricted, repetitive patterns of behaviour, interests, or activities:

• Stereotyped behaviours (e.g., lining up toys, echolalia)
• Insistence on sameness (e.g., rigid thinking)
• Fixated interests (e.g., unusual objects)
• Hyper- or hypo-reactivity to sensory input (e.g., sounds, touch, lights)

All 3 social-communication/social-interaction domains are required, plus at least 2 of 4 restricted/repetitive domains. A checklist of isolated traits is not sufficient.

C. Present in the early developmental period, although features may become fully manifest only when social demands exceed capacity or may later be masked D. Impairment in functioning E. Not better explained by intellectual disability or global developmental delay; ASD and intellectual disability can co-occur when social communication is below that expected for general developmental level

Persistent pattern of inattention and/or hyperactivity-impulsivity

Inattention symptoms (persisting ≥ 6 months; ≥ 6 of 9 for children up to age 16, ≥ 5 for age 17+ and adults):

Careless mistakes, difficulty sustaining attention, doesn't listen, doesn't follow through, difficulty organizing, avoids sustained mental effort, loses things, easily distracted, forgetful

Hyperactivity-Impulsivity symptoms (same age-adjusted count and duration):

Fidgets, leaves seat, runs/climbs inappropriately, can't play quietly, "on the go," talks excessively, blurts out answers, can't wait turn, interrupts others

Present prior to age 12 Several symptoms in 2 or more settings Impairment in functioning Not exclusively during a psychotic disorder and not better explained by another mental disorder

Cluster A: "Odd/Eccentric" — Paranoid, Schizoid, Schizotypal Cluster B: "Dramatic/Emotional" — Antisocial, Borderline, Histrionic, Narcissistic Cluster C: "Anxious/Fearful" — Avoidant, Dependent, Obsessive-Compulsive

The familiar shorthand is A: odd/eccentric, B: dramatic/emotional/erratic, C: anxious/fearful. These are memory aids, not descriptions to apply to a person; diagnose from enduring, pervasive criteria and impairment rather than stereotypes.

Diagnostic Criteria for Borderline Personality Disorder (BPD):

A pervasive pattern of instability of interpersonal relationships, self-image, and affects, and marked impulsivity, beginning by early adulthood, indicated by 5 or more of:

A. Significant cognitive decline from previous level in 1 or more domains: complex attention, executive function, learning and memory, language, perceptual-motor, social cognition — based on informants or cognitive tests B. Interfere with independent living C. Does not occur exclusively in delirium D. Not better explained by another mental disorder

Evidence for decline combines concern from the individual, a knowledgeable informant or clinician and preferably standardised cognitive assessment. The function criterion is the visual discriminator: major NCD interferes with independence in everyday activities; mild NCD does not, although greater effort or compensatory strategies may be needed.

Intermittent explosive disorder, Oppositional defiant disorder, Conduct disorder, Antisocial personality disorder, Kleptomania (stealing), Pyromania (fire setting), OS/US