4.2.1 ICD-11 classification and diagnostic systems

What classification is for

• Classification groups disorders, diagnosis applies a category to one person, and formulation explains that person's difficulties in context.

• Shared categories support communication, research, coding, service planning and treatment decisions.

• A diagnosis needs clinically significant distress or functional impairment: orderly, perfectionist, planned behaviour with neither is normal.

• Distress or social disadvantage alone does not make a diagnosis, but understandable distress can still meet criteria for a treatable disorder.

The ICD-11 framework

The International Classification of Diseases, 11th revision (ICD-11) is the World Health Organization's classification of health conditions. Its clinical descriptions and diagnostic requirements guide the diagnoses in this textbook.

• Clinical judgement applies the requirements to the person's circumstances; a symptom count alone is not a diagnosis.

• Sexual orientation is not a mental disorder, and gender incongruence is classified within sexual health.

Principles of classification

ICD-11 is a descriptive, hierarchical, categorical system that adds dimensional features and permits comorbid diagnoses.

• Categorical classification keeps each disorder distinct and in one place, which lets ICD give uniform case counts for health statistics reported to WHO.

• Operationalised classification defines each disorder by explicit criteria, such as a symptom count, a minimum duration and stated exclusions, to make diagnosis reliable.

• The hierarchical principle ranks disorders so that a lower one is diagnosed only once those above it are excluded, and a higher-order diagnosis absorbs lower-order symptoms.

• Hierarchy does not let psychosis override a mood disorder automatically: chronology and the criteria decide, and a substance-induced or medical syndrome can coexist with an independent disorder.

ICD-11 is partly dimensional in three areas: personality disorder, schizophrenia and other primary psychotic disorders, and depressive episodes.

How a category is built

• Qualifiers refine a diagnosis by subtype, course, severity, remission or associated features, such as melancholia, rapid cycling or insight.

• A symptom checklist alone can misclassify delirium, thyrotoxicosis or stimulant effects as a primary psychiatric disorder, so physical illness, drugs, intoxication and withdrawal are assessed first.

• A provisional diagnosis, ranked differential or unspecified category is better than an unjustified definitive label that persists in later records.

• Reification treats a description as an explanation, and diagnostic overshadowing blames new symptoms on an existing diagnosis, which can delay physical care.

• A formulation sits alongside the diagnosis: predisposing, precipitating, perpetuating and protective factors, the person's priorities and a care plan.

Reliability and validity

• Reliability is consistency between raters or assessments; clear diagnostic requirements and structured assessment can improve it.

• Cohen's kappa corrects agreement for chance but is sensitive to prevalence, so high agreement on negative cases can hide poor recognition of a rare disorder.

• Validity is whether a category identifies a meaningful condition; Robins and Guze listed clinical description, laboratory findings, distinction from other disorders, follow-up and family studies as evidence.

• Applying a rule consistently does not make a category biologically valid, and polythetic criteria allow wide variation within one diagnosis.

• Clinical utility is whether a category improves communication, prediction and treatment.

Recording the whole presentation

ICD-11 does not use a multiaxial system. Record coexisting mental and physical disorders, functioning, disability and relevant psychosocial circumstances, rather than expecting one diagnostic label to describe everything.

ICD-11 structure

• ICD-11 Chapter 6, mental, behavioural or neurodevelopmental disorders, has 21 top-level groupings.

• ICD-11 takes a lifespan approach: conditions such as separation anxiety disorder can be diagnosed in adults when their requirements are met.

• Each diagnosis keeps its own developmental requirements, and behaviour is judged against developmental stage and cultural context.

• Excoriation (skin-picking) disorder, prolonged grief disorder and gaming disorder are distinct ICD-11 diagnoses.

• Selective mutism sits with the anxiety or fear-related disorders, beside separation anxiety disorder, not among the neurodevelopmental disorders.

• The puerperal category with psychotic symptoms takes psychotic syndromes that begin within about six weeks of delivery.

• Sleep-wake disorders and sexual dysfunctions have their own chapters, and gender incongruence sits under sexual health.

• ICD-11 recognises that gender and gender identity vary, so gender variance alone is not a disorder.

• The ICD diagnosis rests on gender identity (incongruence between experienced gender and assigned sex, bodily discomfort, wish to live as the experienced gender), and sexual orientation plays no part.

• Malingering is not a mental disorder: it is coded in chapter 24 among factors influencing health status, whereas feigning without external incentive (factitious disorder) is in chapter 6.

• Paraphilic disorder involving solitary or consenting behaviour needs marked distress about the arousal pattern itself or significant risk of injury or death; distress that only reflects others' disapproval is excluded.

Mood disorders

History

Kraepelin's mixed states arise when mood, thought and activity move in opposite directions at once: a stupor with elevated mood is mixed, whereas a stupor with low mood is pure depression.

Episode durations

Untreated, a manic episode lasts about four months before remitting, and a depressive episode about six months.

Mania and hypomania

• ICD-11 separates mania from hypomania by severity, not symptom list: an episode is manic if it causes marked impairment, needs admission or intensive treatment to prevent harm, or includes delusions or hallucinations.

• Hypomania excludes psychotic symptoms by definition, so their presence makes the episode manic; manic, mixed and depressive episodes can all carry them.

• A full manic syndrome with a fixed grandiose delusion is mania with psychotic symptoms, graded by functional severity and by whether the belief is a true delusion.

• Delusions in mania usually match the elevated mood, so grandiose content is commonest and persecutory ideas come next.

• A first manic episode in a well adult brings elevated mood, less need for sleep, grandiosity and distractibility for over a week, in clear consciousness.

• A low bedside cognitive score explained by distractibility does not imply an organic cause.

Depressive episode

• The core of a depressive episode is low mood or loss of interest, with associated symptoms, present most days.

• ICD-11 grades it mild, moderate or severe by symptom intensity and impairment; moderate means several marked symptoms and considerable difficulty in several domains, with some function kept.

• Delusions or hallucinations can accompany a moderate or severe episode but exclude a mild one, and they do not by themselves decide between moderate and severe.

• ICD-11 qualifiers cover prominent anxiety symptoms, panic attacks, persistent episode, melancholia and seasonal pattern.

• A seasonal pattern is a regular seasonal relationship with episode onset and remission, accounting for a substantial majority of the relevant episodes.

• In young people, depression can show as irritability rather than low mood, with anhedonia, early waking, weight loss and falling function that does not brighten with company.

• Normal adolescence includes arguing with parents, preferring friends to family and sleeping late, with enjoyment and function intact.

• A new episode after a past one is recurrent depression even when anxiety and avoidance are prominent, because low mood, anhedonia and biological symptoms take primacy over secondary worry.

A depressive episode can be diagnosed within weeks of bereavement when the picture goes beyond normal grief.

Mixed states

• A mixed episode has several prominent manic and depressive symptoms together or rapidly alternating, on most days for at least two weeks unless treatment shortens it.

• A depressive mixed state is a full depressive picture with racing thoughts, pressured speech and more goal-directed activity, short of mania.

• Excited depression has overactivity with slowed rather than racing thought.

Bipolar, cyclothymic and recurrent depressive disorders

Tap to enlarge

• An earlier unipolar diagnosis is reviewed when mania or hypomania appears.

• Cyclothymia is under-recognised because its swings are mild and the highs often pleasant; people present with the burden of the lows or with alcohol or drug problems.

• A treatment-emergent affective switch is hypomania or mania arising while a depressed patient takes an antidepressant, with no earlier highs, fading once the drug is withdrawn.

• Bipolar III is an informal term, not an ICD-11 diagnosis. Assess whether a treatment-emergent episode persists beyond the direct treatment effects before assigning a bipolar diagnosis.

• Rapid cycling is four or more mood episodes in 12 months; antidepressant use is the factor particularly linked with it, though the direction of the link is uncertain.

Mood symptoms and psychosis

• Depression arising after a psychotic relapse has settled, with guilt, biological features and residual schizophrenic symptoms, is depressive symptoms within schizophrenia, recorded with the ICD-11 depressive mood symptoms qualifier; assess separately whether a depressive disorder also meets requirements.

• Mood-incongruent psychotic features with formal thought disorder and incongruous affect, without a sustained mood episode, point to schizophrenia rather than psychotic mania, psychotic depression or schizoaffective disorder.

Disorders specifically associated with stress

• Acute stress reaction is an immediate, transient response with daze, agitation and autonomic arousal; ICD-11 does not class it as a mental disorder.

• PTSD requires its characteristic clusters for at least several weeks, with significant impairment; persistence alone does not establish the diagnosis.

• Adjustment disorder brings preoccupation with the stressor and failure to adapt, causing impairment; acute stress reaction follows an exceptionally threatening event, within hours.

• ICD-11 PTSD has three core clusters: re-experiencing in the present with a sense of current threat, avoidance, and hyperarousal such as exaggerated startle.

• Emotional numbing and detachment predict a poor prognosis, with chronic distress, poor interpersonal functioning and lower quality of life.

• ICD-11 complex PTSD needs the full PTSD picture plus three disturbances in self-organisation: affect dysregulation, negative self-concept and relationship difficulty.

• Complex PTSD has a stable, persistently negative self-view, whereas borderline personality disorder has an unstable self-image shifting between positive and negative.

• Names for trauma-related illness moved from shell shock, implying physical injury from the blast, to war neurosis, reflecting the view that stress alone could cause illness.

Anxiety or fear-related disorders

• Generalised anxiety disorder is persistent, hard-to-control worry about several everyday matters on most days for at least several months, with muscular, autonomic and cognitive symptoms and no single trigger.

• A panic attack is a generalised autonomic surge of fear, typed by trigger, timing and symptom count, never by localised origin.

• Panic disorder is defined by recurrent unexpected panic attacks and is coded separately from agoraphobia.

• Agoraphobia is fear of several situations, such as crowds, public transport or being alone away from home, where escape or help would be unavailable.

• Specific phobia is diagnosed only when excessive fear causes avoidance, or endurance with intense fear, and clinically significant distress or impairment.

• Social anxiety disorder is marked fear of scrutiny and negative evaluation across social and performance situations, with avoidance and somatic symptoms; mood is intact away from scrutiny.

• Separation anxiety disorder is fear of being apart from attachment figures, typically worry that harm will befall them.

• School refusal brings physical complaints on school mornings that fade at home and are absent at weekends and holidays, without separation fear.

Selective mutism

• ICD-11 selective mutism needs adequate speech in some settings but consistent failure to speak in others, for at least a month and not confined to the first month of school.

• Silence from unfamiliarity with the language does not count.

• Social anxiety disorder is present in most children with selective mutism.

Obsessive-compulsive or related disorders

• ICD-11 OCD needs obsessions, compulsions or both; obsessions alone are enough, and neither insight nor avoidance is part of the criterion.

• ICD-11 offers an insight qualifier (fair to good, or poor to absent) across this grouping.

• Compulsions can relieve an intolerable sense of incompleteness, driven by rigid rules or a 'not just right' feeling, so OCD stands when no feared consequence is reported.

• Checking is the most frequently reported compulsion, ahead of washing, counting and ordering; washing follows the commonest obsession, contamination.

• OCD has ego-dystonic obsessions driving a rule-bound compulsion with no realistic link to the feared outcome, unlike the diffuse, shifting worry of generalised anxiety disorder.

• Intrusive OCD images are recognised as the person's own, whereas PTSD images are relivings of a real trauma.

• Hoarding within OCD neutralises obsessional anxiety and stays unwanted and distressing; in hoarding disorder saving is value-driven and may be enjoyed, and the amount kept does not separate them.

• Hypochondriasis is persistent preoccupation with having a serious disease despite negative tests and reassurance, with fear of the disease, not the symptom, driving repeated consultation.

• Hypochondriasis is 'with poor to absent insight' when conviction of illness stays fixed despite negative tests and reassurance and is unchanged when the person is calm.

Bodily distress and dissociative disorders

Bodily distress or bodily experience

• Bodily distress disorder involves distressing bodily symptoms with excessive attention that persists despite appropriate assessment and reassurance, on most days for at least several months.

• It typically presents with several shifting symptoms, and a coexisting or contributing medical condition does not exclude it when attention is clearly disproportionate.

• It lacks hypochondriasis's fear of a serious undiagnosed illness.

• Symptoms do not have to be medically unexplained; assess the degree of attention and impairment in context.

• Briquet's syndrome is a historical description of multiple shifting physical symptoms; current diagnosis requires the ICD-11 bodily distress features rather than an unexplained-symptom count.

• Neurasthenia is not a separate ICD-11 diagnosis; reassess fatigue and bodily symptoms rather than assuming they meet bodily distress disorder requirements.

• Body integrity dysphoria is a persistent, childhood-onset desire for a specific physical disability, with distress from the non-disabled body.

• It has no concern about appearance, unlike body dysmorphic disorder, and is ego-syntonic and unresisted, unlike the intrusive, resisted obsessions of OCD.

Dissociative

• Dissociative neurological symptom disorder involves involuntary motor, sensory or cognitive symptoms inconsistent with recognised neurological disease; a preceding stressor is not required.

• Depersonalisation-derealisation disorder is persistent or recurrent depersonalisation (self, body or actions feel unreal or detached), derealisation (surroundings feel unreal or dreamlike) or both, with reality testing intact.

• Dissociative fugue is purposeful travel with preserved self-care and loss of personal identity, often with a new name, after a stressor; dissociative amnesia has the memory loss without journey or new identity.

• Fugue is classified within dissociative amnesia (ICD-11 with or without fugue), not as its own disorder.

• Ganser syndrome brings approximate answers that just miss, clouded consciousness and later amnesia, classically in a man facing trial.

• Ganser syndrome may be recorded under other specified dissociative disorders in ICD-11 after alternative causes are assessed.

Schizophrenia: history and concepts

Kraepelin and Bleuler

• Emil Kraepelin created dementia praecox in the 1899 edition of his textbook, uniting catatonia, hebephrenia and paranoid states.

• Kraepelin divided the major psychoses by longitudinal course: early-onset, chronic, deteriorating dementia praecox with no recovery, against relapsing and remitting manic-depressive insanity.

• Eugen Bleuler introduced schizophrenia in 1908, replacing dementia praecox, and set it out in his 1911 monograph.

• He named it for loosening of associations and the split between thought and affect, and did not accept that every patient deteriorated.

• Bleuler's fundamental symptoms, present in every case, are the four As: loosened associations, affect, ambivalence and autism; alogia is not among them.

• His accessory symptoms (hallucinations, delusions, catatonia) are common but not needed; Schneider's first-rank symptoms belong to this accessory tier.

• Bleuler added simple schizophrenia to the existing subtypes, fitting his view that positive psychotic features were not necessary.

Other names and terms

• Jacob Kasanin coined schizoaffective psychosis in 1933 from nine young patients with good premorbid adjustment, whose abrupt post-stress psychoses blended schizophrenic and affective features and resolved fully within months.

• Schizoaffective disorder sits at the intermediate point between schizophrenia and mood disorder on a unitary psychosis continuum; its nosological status is otherwise contested.

• Crow's 1980 model divides schizophrenia into type I (positive symptoms, acute course, good drug response, dopamine change) and type II (negative symptoms, cognitive impairment, poor response, enlarged ventricles, structural change).

• Crow did not originate the positive and negative distinction.

• Paranoia comes from the Greek para (beside) and nous (mind), literally beside the mind.

Concepts

• Kurt Schneider originated the first-rank symptoms, which are not specific: about 10% of people with other psychotic illnesses show one or more, up to about 19% when studies look for them directly.

• Impaired insight was the most frequent single feature of schizophrenia in the WHO International Pilot Study of Schizophrenia, consistent across cultures.

• Secondary negative symptoms have an identifiable external cause: positive symptoms, depression, antipsychotic side effects or understimulation.

• Childhood socioeconomic disadvantage, measured as low or falling parental income, is linked with a higher later risk of schizophrenia.

• The oneiroid state is a dream-like, immersive, scenic hallucinatory experience with some clouding of consciousness, accompanying catatonia in acute schizophrenia.

Historical subtypes

Paranoid, hebephrenic, catatonic, residual and simple schizophrenia are older labels. ICD-11 replaces subtypes with symptom and course qualifiers; these historical descriptions do not establish a current diagnosis.

Schizophrenia in ICD-11

ICD-11 schizophrenia needs at least two of seven symptom groups, at least one from the four core groups.

• ICD-11 requires the symptoms most of the time for at least one month, without counting any prodromal or residual phase.

• ICD-11 replaces subtypes with symptom and course specifiers, and keeps schizoaffective and schizotypal disorder within the grouping.

• ICD-11 rates six symptom domains (positive, negative, depressive mood, manic mood, psychomotor, cognitive), which belong to the primary psychotic grouping only, not to a mood disorder with psychotic features.

• The continuous course specifier applies when full requirements are met for nearly all of a course lasting a year or more, with only brief subthreshold spells, including a first episode lasting over a year.

Late life

• Late-onset schizophrenia shows a female excess, prominent hallucinations, fewer negative symptoms, less formal thought disorder, lower family loading, sensory impairment and premorbid paranoid or schizoid traits.

• Very-late-onset schizophrenia-like psychosis starts after 60, with a partition delusion, persistent voices, female sex, isolation and uncorrected hearing loss, and intact cognition and self-care.

Other primary psychotic disorders

Delusional disorder

• Content is usually stable and circumscribed, such as persecutory, jealous or somatic beliefs; passivity experiences or other characteristic schizophrenia symptoms point elsewhere.

• There are no hallucinations, thought disorder or mood disorder, except occasional hallucinations tied to the theme (ICD-11), such as crawling or biting skin sensations in delusional infestation.

• Affect, speech and behaviour outside the delusional theme are largely preserved.

• It begins in middle adult life with a persistent course and preserved functioning, later and less deteriorating than schizophrenia.

• Record the delusional theme clinically; ICD-11 uses course qualifiers rather than a fixed list of thematic subtypes.

• Induced delusional disorder (folie à deux) is a delusion passing from a primary patient to a closely tied associate, often a relative in relative isolation, and usually fading once the two are separated.

• It arises mostly within the nuclear family; couples are the most frequently reported pairing, sisters next.

Schizotypal disorder

• ICD-11 places schizotypal disorder with schizophrenia and other primary psychotic disorders, outside the personality disorders.

• It brings odd dress, vague or circumstantial speech, magical thinking, illusions, ideas of reference, paranoid ideation and social anxiety that does not ease with familiarity, so the person seems eccentric or nonconformist.

• Fixed delusions or hallucinations are psychotic-level symptoms that fall outside it.

Catatonia, organic and late-life presentations

• Catatonia during an established primary mental disorder is catatonia associated with another mental disorder (ICD-11), once substance, medication and medical causes are excluded.

• Delirium (acute confusional state) is an acute, fluctuating disturbance of attention, orientation and arousal, often worse at night, with lucid spells and a physical precipitant.

• Alcohol withdrawal delirium differs from other delirium by needing recent heavy drinking and autonomic signs.

• Visual hallucinations, often of people or animals, outnumber other modalities in delirium.

• Delirium may persist after the precipitating illness improves; a prolonged course needs reassessment of ongoing causes and baseline cognition.

• Dementia with Lewy bodies shows fluctuating cognition and attention, recurrent well-formed visual hallucinations of people or animals, rapid eye movement (REM) sleep behaviour disorder and parkinsonism.

• ICD-11 frontotemporal dementia has insidious onset, gradual worsening, behavioural or language variants, and early sparing of memory, psychomotor speed and visuoperceptual and visuospatial ability.

• Diogenes syndrome is severe self-neglect and domestic squalor with withdrawal and calm refusal of help, often in capable people living alone; hoarding disorder's core is difficulty discarding possessions.

Substance use, addictive behaviours and sleep

• ICD-11 allows alcohol dependence after 3 months of daily or near-daily drinking, though the features are usually expected over 12 months; the 1-month threshold belongs to harmful pattern of use.

• ICD-11 separates an episode of harmful use from a harmful pattern of use; harm may affect the user's health or others' health through substance-related behaviour.

• The Edwards and Gross (1976) alcohol dependence syndrome has seven elements and keeps harm from drinking outside the definition.

• Salience in that syndrome is drinking outranking other priorities and pleasures, reordering the rest of life.

• Alcoholic hallucinosis (alcohol-induced psychotic disorder with hallucinations) begins with heavy drinking and continues in clear consciousness after stopping, without withdrawal signs, lasting under a month.

• Alcoholic hallucinosis usually resolves quickly once drinking stops, and persisting symptoms respond to antipsychotics.

• Caffeine intoxication follows recent use with clinically significant changes such as restlessness, tremor, insomnia or tachycardia; susceptibility varies and ICD-11 sets no fixed dose threshold.

• Excessive daytime sleepiness with cataplexy, a brief emotion-triggered loss of muscle tone with preserved awareness, identifies narcolepsy.

Personality disorders

ICD-11 model

• ICD-11 personality disorder is a pervasive disturbance of self and interpersonal functioning over an extended period, typically two years or more; the two-year figure is an example, not a fixed minimum.

• ICD-11 uses one diagnosis graded by severity, plus optional trait domain qualifiers.

• The five trait domains are negative affectivity, detachment, dissociality, disinhibition and anankastia, with an optional borderline pattern specifier.

• Negative affectivity is broad, intense negative emotion with poor regulation, low self-esteem, negativistic attitudes and mistrust.

• Severity reflects the extent of self and interpersonal dysfunction, impairment and harm; trait qualifiers describe the pattern rather than determine the grade.

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Clinical personality patterns

The following names describe familiar clinical patterns in older literature. They are not separate ICD-11 personality disorder categories; record severity and the relevant trait domains. Schizotypal disorder belongs to the primary psychotic disorders.

• The avoidant person still wants contact, whereas the schizoid person has no wish for closeness.

• Histrionic emotion is shallow and played to an audience, whereas borderline mood swings are intense, deeply felt and triggered by interpersonal stress.

• OCD obsessions are ego-dystonic, unwanted and recognised as senseless, whereas obsessive-compulsive personality traits are ego-syntonic and felt as reasonable; ICD-11 captures the personality pattern with the anankastia qualifier.

Borderline pattern

• The ICD-11 borderline pattern qualifier accompanies personality disorder severity and requires at least five of nine characteristic features.

• Up to three quarters report childhood physical or sexual abuse and prolonged early separation, with insecure attachment as the proposed link.

• Childhood sexual abuse has the most consistent, replicated association with borderline personality disorder of any childhood adversity.

• Impulsive and self-destructive behaviour improves soonest, with or without treatment, while dysphoria, anger, emptiness and abandonment concerns are the most stable.

• Borderline and schizotypal personality disorders cause the most occupational impairment, avoidant is intermediate and obsessive-compulsive least (Skodol and colleagues, 2002, Collaborative Longitudinal Personality Disorders Study).

Dissocial pattern

• Dissociality is disregard for others' rights and feelings, with self-centredness, lack of empathy and potentially deceitful or exploitative behaviour.

• Impulsivity is described separately by disinhibition; add it only when prominent.

• ICD-11 personality disorder has no universal minimum age of 18, but an enduring disturbance must be distinguished from normal adolescent development.

Disruptive behaviour and impulse control

• Conduct disorder is a persistent pattern of serious rule violation, such as truancy, staying out at night against parental rules and theft.

• Oppositional defiant disorder is defiance without serious violation of rules or others' rights.

• Callous-unemotional traits (the 'with limited prosocial emotions' specifier) bring under-arousal, fearlessness, reduced physiological response to distress, low guilt, shallow affect, novelty-seeking and instrumental aggression.

• In ICD-11 'with limited prosocial emotions' is available for both oppositional defiant and conduct-dissocial disorder, and signals a worse outlook.

• Intermittent explosive disorder and oppositional defiant disorder with chronic irritability-anger both show disproportionate outbursts; significant physical aggression leans towards the former, and defiant, headstrong or vindictive behaviour belongs to the latter only.

Feeding and eating disorders

Anorexia nervosa

• Anorexia nervosa rests on a triad: significantly low body weight, persistent restriction or other behaviour preventing weight restoration, and weight or shape dominating self-evaluation.

• ICD-11 no longer requires endocrine disturbance such as amenorrhoea, and thyroid results are not part of the criteria.

• ICD-11 uses no fixed body mass index (BMI): the adult threshold of 18.5 kg/m2 is a guideline, and loss of over 20% of body weight within six months can replace it.

• ICD-11 classes anorexia by weight band (significantly low; dangerously low, with BMI under 14.0; in recovery at normal weight) and by pattern (restricting or binge-purge).

• Unreported shape and weight preoccupation is inferred from monitoring and checking, including seeking weight-loss advice, and from extreme avoidance of size cues.

• When full criteria are met, they displace the residual other specified category (atypical anorexia nervosa).

• Monozygotic twin concordance exceeds dizygotic concordance, the twin evidence for heritability.

• There is no consistent social class gradient, so the picture of an illness of affluent Western families is not borne out.

Bulimia nervosa and binge-eating disorder

• Bulimia nervosa is recurrent binge eating followed by repeated compensatory behaviour, typically purging; Gerald Russell first described it as a syndrome in 1979.

• Bulimia is told from binge-eating disorder by regular compensatory behaviour, which need not be purging (fasting or driven exercise count), at a weight that is not significantly low.

ARFID

• ARFID is restrictive or avoidant eating without weight-and-shape psychopathology, whereas restriction in anorexia nervosa is driven by fear of weight gain or pursuit of thinness.

• Weight loss, nutritional compromise and impairment do not separate ARFID from anorexia nervosa.

• Restriction is driven by sensory features, fear of an aversive consequence of eating (choking, vomiting, pain) or low interest in food, often with a wish to gain weight.

• ARFID is the eating disorder most associated with autism spectrum disorder, through shared sensory sensitivity.

Neurodevelopmental and early-childhood disorders

Autism spectrum disorder

• ICD-11 treats autism spectrum disorder as one category, with qualifiers for intellectual development, functional language and loss of previously acquired skills.

• It spans every level of language and intellectual ability, so impaired reciprocal social communication with preserved language is autism spectrum disorder, not a separate category.

• It usually first becomes evident in the second year of life, at 12 to 24 months.

• Lorna Wing and Gould's 1979 Camberwell work proposed the triad of impairments (social interaction, communication, imagination), later collapsed into the current social-communication and restricted-behaviour dyad.

• Social communication is abnormal, with odd prosody, formal or pedantic speech and limited gesture and gaze.

• A young child may show delayed echolalia, pronoun reversal, poor eye contact, distress at change and restricted, repetitive behaviour.

• Asperger syndrome is a legacy label; ICD-11 assesses autism spectrum disorder and describes intellectual and language functioning separately.

ADHD, intellectual disability and attachment

• ADHD has three core features: inattention, hyperactivity and impulsivity; ICD-11 requires significant symptoms before age 12, although diagnosis may occur later.

• ICD-11 sets the threshold for a disorder of intellectual development at about two or more standard deviations below the mean (roughly the 2.3rd percentile), in intellectual functioning and adaptive behaviour.

• ICD-11 reactive attachment disorder is a child who, after grossly inadequate early care, seeks and accepts little or no comfort from any adult, even an adequate new caregiver.