• To learn the basic principles underlying the classification of psychiatric illness
• To learn the diagnostic criteria of common psychiatric illness

This lecture is the single most frequently tested topic in psychiatry SAQs/MCQs at HKUMed — past papers repeatedly ask for classification systems, reasons for classification, diagnostic criteria of specific disorders, and the concept of psychotic vs non-psychotic phenomena. It is also the foundation for every subsequent GC psychiatry lecture.

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 are qualitatively different from normal experience. A healthy person does not hear voices discussing them in the third person. These are the hallmark of psychotic disorders.

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

Everyone feels sad sometimes. Everyone worries. The difference in psychiatric illness is that these normal emotions become quantitatively excessive — they dominate the person's life, are disproportionate to the stimulus, and the person cannot control them. This is the domain of mood disorders, anxiety disorders, OCD, and PTSD.

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 are disorders where a basic physiological function is disrupted.

Addiction, including non-substance (e.g., gambling) Impulse-control disorder (e.g., trichotillomania)

The person cannot stop a behaviour despite negative consequences.

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.

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
• Overlap categories when biology overlaps — e.g., schizoaffective disorder bridges schizophrenia and mood disorders

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.

Use open-ended questions in history taking

• Example: "How is your sleep in the past week?" Avoid close-ended questions
• Bad example: "Do you have poor sleep?" Ask patients to elaborate Focus on one symptom at a time

Why open-ended? Because close-ended questions suggest the answer and can lead to false positives (patient agrees with whatever you suggest). Open-ended questions let the patient describe their experience in their own words, yielding richer and more accurate information.

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 mean they have the diagnosis. Examiners love testing this distinction.

Schizophrenia Spectrum and Other Psychotic Disorders:

Diagnostic Criteria for Schizophrenia (DSM-5):

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)

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.

Criterion D — Exclusion: Schizoaffective and mood disorders ruled out; not attributable to substance/general medical condition

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

68-year-old divorced man, 6 weeks of 3rd person auditory hallucinations + thought broadcasting + ideas of reference (newspaper/TV talking about him) + disorganized speech + poor self-care + negative symptoms (dull, stays home). 8th episode over 30 years. Progressive functional decline. Poor insight.

This vignette illustrates:

• Multiple Criterion A symptoms (hallucinations, disorganized speech, negative symptoms)
• Functional decline (Criterion B) — former university student → unemployed, divorced
• Duration > 6 months (Criterion C) — 30-year history
• 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:

• Not meet criteria for bipolar mixed episode
• Clinically significant distress or impairment
• Not due to substance or general medical condition
• Not better accounted for by bereavement (persisting > 2 months or with marked features)

A distinct period of (1) elevated, expansive, or irritable mood AND (2) increased goal-directed activities for at least 1 week, PLUS 3 or more of:

Mood Disorders Classification from the lecture:

Depressive disorders: single/recurrent episodes, dysthymia, PMDD Bipolar disorders: both manic/hypomanic/mixed AND depressive episodes occur in lifetime

• Manic/hypomanic/mixed episodes usually last for a week
• Depressive episodes can last for weeks or months
• Usually symptom-free during inter-episode period
• 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 due to substance or general medical condition

A discrete period of intense fear or discomfort, with 4 or more of the following developing abruptly and peaking within 10 minutes:

B. Recurrent unexpected attacks for at least 1 month

Key distinction: Panic attacks in panic disorder are unexpected (out of the blue). If attacks only occur in specific situations (e.g., only in social settings), consider social phobia with panic attacks rather than 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. For 3 months E. Severity by BMI: Mild ≥ 17; Moderate 16–16.99; Severe 15–15.99; Extreme < 15 F. Subtypes: Restricting type vs Binge-eating/purging type

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 other sleep disorder, substance, mental or medical condition Primary or Comorbid insomnia

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)

C. Present since childhood D. Impairment in functioning E. Not better explained by intellectual disability or global developmental delay

Persistent pattern of inattention and/or hyperactivity-impulsivity

Inattention symptoms (≥ 6 of 9):

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 (≥ 6 of 9):

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 In 2 or more settings Impairment in functioning Not exclusively during other disorders

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

Mnemonic:

• Cluster A = "Aloof" (weird, withdrawn)
• Cluster B = "Bad" (dramatic, erratic)
• Cluster C = "Cowardly" (anxious, avoidant)

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. Not better explained by another mental disorder

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

A cleaning worker with persistent severe back pain > 2 years, multiple investigations normal, overwhelmed by symptoms, ongoing compensation claim — most likely diagnosis: Somatic Symptom Disorder (previously called Somatoform Disorder).

The 3P model:

• Predisposing factors: Anxious-prone personality
• Precipitating factors: Fall from stool (physical injury)
• Perpetuating factors: Ongoing compensation claim (secondary gain), lack of diagnosis, smoking/drinking

36-year-old, 4 weeks postpartum, low mood, guilt, fleeting suicidal thoughts about jumping — Postpartum depression (not puerperal blues which resolves by 2 weeks, not puerperal psychosis which involves psychosis, not normal reaction given the suicidal ideation).

Which psychiatric condition can mimic dementia? → Depressive disorder (known as "pseudodementia" or "depressive pseudodementia")