Classification of diseases and the neurodevelopmental disorders: the challenge for DSM‐5 and ICD‐11

Fundamental to communication about and research into diseases is a diagnostic classification system based on phenomenology and pathophysiology. There are two major diagnostic classification systems for mental and behavior disorders in current use: the DSM-IV published by the American Psychiatric Association and the ICD-10 published by the World Health Organization.1, 2 Each includes the neurodevelopmental disorders affecting coordination, speech, language, and specific academic learning; and in addition autism, attention-deficit–hyperactivity disorder, tics and Tourette disorder, stereotyped movements, and intellectual disability. Both the DSM-IV and ICD-10 are currently being revised and I have been privileged to be a member of the neurodevelopmental work groups for both systems. The challenges to revision are many – including whether change is needed at all! Some have proposed a radical merger for the ICD-10 of mental and behavioural disorders with neurological disorders, arguing that organic/inorganic distinctions are no longer tenable,3 but that may be for future editions. Hyman has written about the dangers of 'reification'; that simply by creating classification systems, research is inhibited into whether the diagnoses are 'real' or not.4 A number of the current diagnoses are seldom used. A further challenge is the recognition that many disorders that were once considered categorical are now considered dimensional.5, 6 Working in the field of neurodisability what had struck me most forcibly about the current classification systems was how frequently the children and young people I met did not quite meet criteria for certain disorders, necessitating a 'not otherwise specified' diagnosis; how they seemed to change from one diagnosis to another as they grew older; how variably different clinicians used certain diagnoses (notably Asperger disorder, autism, and pervasive developmental disorder not otherwise specified [including atypical autism]); and also how often the children and young people seemed to have a complicated mix of disorders which was not allowed for by the diagnostic systems. One agreeable feature of sharing experiences in the workgroups with others from across the globe is that they had found the same. The American Psychiatric Association and World Health Organization have each approached the task from a different basis but with an intention to harmonize. For both systems reliability, validity, and utility are important. The DSM is a classification system setting criteria for diagnosis and research, which is also a clinical tool and the basis of remuneration in the USA. The World Health Organization's priority is a broader utility and the ICD-11 is intended to have clinical, teaching, training, and health statistics use world-wide not only for mental health professionals but importantly for primary care staff and others across many different cultural settings. More contentiously, in the western world, both diagnostic systems have moved beyond medical classification and been used to set eligibility for both services and benefits. A major change has been that during the current revision of the DSM-IV the importance of the classification system to users, i.e. those with mental, behavioural, and neurodevelopmental problems themselves, has been recognized and public involvement has been sought. The DSM-5 proposals have attracted a large number of comments both positive and negative including the view that 'normality' is being medicalized. What we do know about the pathophysiology of neurodevelopmental and mental and behavioural disorders indicates a complex mix of genetic and non-genetic risk factors. In the absence of biomarkers, diagnostic criteria for mental and behavioral disorders will continue to depend upon surface features of behavior (i.e. phenomenology), but the work groups have proposed that diagnoses without a clear scientific basis will be removed. As an example, in the DSM-5, autism spectrum disorder replaces autism, Asperger disorder, childhood disintegrative disorder, and pervasive developmental disorder not otherwise specified thus 'lumping' rather than 'splitting' and leaving the field open for future research into more valid subgroups. The uniqueness of the individual will be recognized by specifying pattern of onset, course, and associated descriptive features (e.g. intellectual ability). Dimensions will be recognized by promoting a quantitative approach to symptom severity and while symptoms have to be impairing of everyday function for the diagnosis of a disorder in DSM-5, the framework of the ICF7 is promoted as the basis of measurement of impairment for the individual. Whether this is regarded as progress by other users remains to be seen but I think description of the individual, their strengths and weaknesses, other problems, and hence their needs will be an improvement.