History of psychiatry. Classification of mental disorders according to the International Classification of Diseases – 10th edition (ICD-10)

01History of psychiatry

Psychiatry, the medical study and treatment of mental disorders, is older than its name, which Johann Christian Reil coined in 1808. Each period of its history left something still in use: the idea that mental illness is a bodily disorder, the hospital, careful description, physical and psychological treatments, and care in the community.

From the humours to the asylum

Hippocratic medicine placed the mind in the brain and explained mental illness by an imbalance of the four humours: melancholia was an excess of black bile, and On the Sacred Disease argued that epilepsy had a natural cause. Hospitals of the medieval Islamic world, in Baghdad, Damascus and Cairo, had wards for the mentally ill. In Christian Europe most care fell to families and religious houses, and supernatural explanations lived beside the humours. Bethlem in London took in "lunatics" from about 1400 (its name became "bedlam"), and Valencia's hospital of 1409 was among the first in Europe built for them.

In the 17th century the general hospitals of Paris and other cities confined the insane with the poor and vagrant, often in chains. Moral treatment answered this in the 1790s: Vincenzo Chiarugi in Florence, Philippe Pinel with the superintendent Jean-Baptiste Pussin at the Bicêtre and the Salpêtrière in Paris, and the Quaker William Tuke, who opened the York Retreat in 1796. They freed patients from chains and treated them with kindness, routine and occupation. Pinel's pupil Jean-Étienne Esquirol described illnesses at the bedside and defined the hallucination as a perception without an object (1838).

The 19th century built public asylums across Europe. They began with hope but grew overcrowded and custodial. Wilhelm Griesinger taught that mental illnesses are diseases of the brain (1845), and the finding of Treponema pallidum in the brains of patients with general paresis of the insane (1913) proved it for one common asylum illness.

Describing and naming the illnesses

The late 19th century described the syndromes the classifications still use: Ewald Hecker's hebephrenia (1871), Karl Kahlbaum's catatonia (1874), Sergei Korsakoff's amnesic syndrome (1887) and Alois Alzheimer's presenile dementia (1906).

Bleuler's word is often misread: schizophrenia does not mean a split or multiple personality, a mistake that still feeds stigma.

Physical treatments, and abuses

Julius Wagner-Jauregg's malaria therapy for general paresis (1917) won psychiatry's first Nobel Prize, in 1927. Insulin coma (Manfred Sakel, 1933) and convulsions induced with camphor and then cardiazol (Ladislas Meduna, 1934) followed, and Ugo Cerletti and Lucio Bini gave the first electrically induced seizure in Rome in 1938. Of these only electroconvulsive therapy survives, now under anaesthesia and a muscle relaxant. Egas Moniz's prefrontal leucotomy (1935) also won a Nobel Prize, and tens of thousands of operations followed before it was abandoned for the harm it did.

Psychiatry was also used to harm. Nazi Germany sterilised mentally ill and disabled people by force and, from 1939, killed psychiatric patients: more than 70,000 in the gas chambers of the T4 programme in 1940 and 1941 alone, and many more after it. In the Soviet Union dissidents were detained in psychiatric hospitals under diagnoses such as "sluggish schizophrenia", stretched to fit dissent. These histories are why consent, mental health law and human rights now stand at the centre of practice.

The drug era and deinstitutionalisation

1. 1949

   Lithium

   In Melbourne John Cade reports that lithium calms manic patients. Mogens Schou's trials in Denmark from 1954 establish it.

2. 1952

   Chlorpromazine

   Jean Delay and Pierre Deniker in Paris give chlorpromazine to psychotic patients: the first antipsychotic.

3. 1957

   The first antidepressants

   Roland Kuhn in Switzerland reports the effect of imipramine, the first tricyclic, and iproniazid, a tuberculosis drug, becomes the first monoamine oxidase inhibitor used in depression.

4. 1958 to 1963

   Haloperidol and the benzodiazepines

   Paul Janssen in Belgium makes haloperidol. Chlordiazepoxide, the first benzodiazepine, comes in 1960 and diazepam in 1963.

5. 1959 to 1978

   The asylums empty

   Asylum populations fall from their peak in the mid-1950s. The Mental Health Act 1959 for England and Wales makes informal admission, without any forms, the usual route into hospital, Erving Goffman's Asylums (1961) and the anti-psychiatry movement attack the institution, and Italy's Law 180 of 1978, led by Franco Basaglia, closes its asylums to new admissions.

6. 1975 to 1990

   Clozapine

   Clozapine is withdrawn in several countries after deaths from agranulocytosis. A trial in 1988 shows that it works when other antipsychotics have failed, and it returns with blood monitoring.

7. Late 1980s

   The SSRIs

   Fluoxetine, the first widely used selective serotonin reuptake inhibitor, reaches the market; the newer antipsychotics follow in the 1990s.

8. 2019

   New mechanisms

   Esketamine nasal spray, acting on glutamate rather than the monoamines, is authorised in the European Union for treatment-resistant depression.

The drugs did not empty the asylums alone: social psychiatry, criticism of institutional life (Russell Barton's "institutional neurosis", 1959) and the cost of the old hospitals pushed the same way. Many patients gained freedom and better lives, but thin community services also brought a "revolving door" of readmission, homelessness and imprisonment of people with severe mental illness.

Psychiatry now

• Care in the community: community mental health teams, crisis and home treatment, early intervention for a first psychosis, units in general hospitals, and psychosocial rehabilitation built round the recovery model.
• The biopsychosocial model (George Engel, 1977): each disorder is understood, and treated, through its biological, psychological and social causes.
• Evidence: randomised trials and meta-analyses, national guidelines (in the UK, NICE since 1999), and psychological treatments tested like drugs, such as cognitive behavioural therapy.
• Neuroscience and genetics: imaging, and genome-wide studies that find hundreds of common variants of small effect (see neurobiology and genetics).
• Rights: mental health laws that limit and review detention, the UN Convention on the Rights of Persons with Disabilities (2006), and the involvement of service users.

02Classification of mental disorders

Why classify

A diagnosis lets clinicians communicate in a word, predict the course, choose a treatment, study comparable patients, count disorders and plan services. It also has costs: a label can stigmatise, can pass for an explanation, and can hide the individual. It is justified only when it helps the patient.

The ideal classification sorts diseases by cause. The causes of most mental disorders are unknown, so psychiatry defines syndromes: groups of symptoms and signs with a typical course. A diagnosis is reliable when clinicians agree on it, and valid when it corresponds to a real, distinct condition; psychiatry has worked hardest on reliability.

The principles behind ICD-10 and DSM

Operational criteria answered a crisis of reliability. Around 1970 the US–UK Diagnostic Project found that New York psychiatrists diagnosed schizophrenia far more often than London psychiatrists in similar patients, until a standardised interview closed the gap. Research criteria in the 1970s, then DSM-III in 1980, defined each disorder explicitly, and ICD-10 followed.

Categories are a convention: most symptoms lie on a continuum with normal experience, and severity scales and personality traits treat them as dimensions, as ICD-11 partly does. Two old words survive as descriptions: psychotic symptoms (hallucinations, delusions, grossly disorganised behaviour) lose contact with reality, while neurotic symptoms, such as anxiety and obsessions, exaggerate normal experience with insight kept. ICD-10 no longer divides disorders into psychoses and neuroses, although "neurotic" stays in the name of its F4 block.

ICD-10 chapter V

The International Classification of Diseases is the WHO's classification of all diseases; mental disorders first had their own section in ICD-6 (1948). ICD-10 was endorsed in 1990 and came into use from 1994. Its mental disorders are chapter V, F00 to F99.

1. 1

   The letter

   F marks a mental or behavioural disorder.
2. 2

   The first digit

   The block: F2 is schizophrenia and related disorders, F3 the mood disorders.
3. 3

   The second digit

   The category: F32 a depressive episode, F33 recurrent depressive disorder. In F1 it names the substance: F10 is alcohol.
4. 4

   After the point

   The subtype or state: F32.2 severe depressive episode without psychotic symptoms, F20.0 paranoid schizophrenia, F10.3 alcohol withdrawal; .8 means other and .9 unspecified.

In the F1 block the character after the point is the same for every substance: .0 acute intoxication, .1 harmful use, .2 dependence syndrome, .3 withdrawal state, .4 withdrawal with delirium, .5 psychotic disorder, .6 amnesic syndrome, .7 residual and late-onset psychotic disorder. So F10.4 is delirium tremens and F10.6 Korsakoff syndrome.

Chapter V comes in versions for different users: the Clinical Descriptions and Diagnostic Guidelines (the "blue book", 1992), with room for clinical judgement; the Diagnostic Criteria for Research (the "green book", 1993), stricter, for homogeneous research groups; a primary care version; and a multiaxial version with three axes, the clinical diagnoses (mental and physical, with personality disorder and intellectual disability), disabilities (rated 0 to 5 in personal care, work, family and social life), and contextual factors, coded with the Z codes. Several countries use national versions, such as Germany's ICD-10-GM.

03DSM-5-TR and ICD-11

DSM-5-TR compared with ICD-10

The American Psychiatric Association's manual began in 1952 (DSM-I). DSM-III (1980) brought operational criteria and five axes; DSM-5 (2013) dropped the axes; and DSM-5-TR (2022) added prolonged grief disorder and codes for suicidal behaviour and non-suicidal self-injury. It has no codes of its own and uses those of ICD-10-CM.

ICD-11

ICD-11 was adopted by the World Health Assembly in 2019 and has been in force since 1 January 2022. Its mental disorders are chapter 6, coded from 6A00 (6A20 schizophrenia, 6A71 recurrent depressive disorder), and its diagnostic manual followed in 2024. It was developed alongside DSM-5, so the two are now close in structure. Countries move to it slowly, and most European health systems still code with ICD-10 or a national version of it.