Neurodevelopmental conditions are defined in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5)1 and the 11th edition of the International Classification of Diseases (ICD-11)2 as conditions that arise early in development. They include attention-deficit/hyperactivity disorder (ADHD), autism, intellectual disabilities, communication disorders, specific learning disorders (e.g., dyslexia), and motor disorders that include developmental co-ordination disorder (and tic disorders in the case of DSM-5).
Conceptual Differences
There is a rationale for grouping these conditions3 insofar as they typically arise early in development, although they may not be identified until later. Neurodevelopmental conditions show strong overlap with each other and share risk factors in common, including family history and genetic liability. Typically, the clinical course of neurodevelopmental conditions, except for tic disorders, tends to change with maturation but otherwise usually shows a relatively steady state, rather than display a remitting and relapsing pattern. They also do not behave as clear-cut yes/no diagnostic categories; rather, they each lie on a continuum. Finally, neurodevelopmental conditions often are associated with educational differences and challenges. This spectrum of variation has led to interest in the term neurodivergence (ND) and a shift away from using the term disorder outside clinical settings.4
Many but not all the features described above separate neurodevelopmental conditions from mental health conditions such as anxiety, depression, eating disorders, and psychosis. Mental health challenges typically arise later in development than ND, with most having an onset in adolescence and early adult life. They also often show patterns of remission and relapse rather than stability.3
Thus, there are important conceptual reasons for separating or splitting neurodevelopmental and mental health conditions as is done by both the DSM-5 and ICD-11 diagnostic systems.
However, what is happening in many parts of the United Kingdom and other countries is that services and funding for neurodevelopmental conditions/neurodivergence, at least for autism, ADHD, and Tourette’s syndrome, are being separated from those for mental health. In my view, this is a problem. Why? The most important reason is that there is such a strong clinical overlap between neurodevelopmental and mental health conditions. Autism, ADHD, and Tourette’s syndrome commonly co-occur with anxiety, obsessive-compulsive disorder, depression, posttraumatic stress disorder, eating disorders, bipolar disorder, and schizophrenia.5–9
Problems With Separating Funding
Separate ND and mental health funding and services leads to the following problems:
First, those with a neurodevelopmental condition who present to mental health services may fail to have ND identified, or if it is, then this leads to referral to a different service and waiting on a separate list for support.
Equally, those who are under the care of a neurodevelopmental service who then develop a mental health condition also would have to be referred to a different service, and their mental health condition may not be recognised by the ND service. This lack of a single front door and a person-centric approach means that timely support is delayed and adds to system inefficiencies and unnecessary costs: both human and economic.
Second, it can lead to deskilling of professionals, where those in mental health services are no longer trained to identify and assess ND and thus cannot effectively treat the mental health challenge. Let us take the example of an adolescent who presents to a child and adolescent mental health service with severe depression. The clinician identifies ADHD but is not “allowed” to treat ADHD, only the depression, even though it is untreated ADHD that underlies the development and maintenance of depression. The clinician must refer the young person to a neurodevelopmental service.
There is now much research highlighting that diagnostic siloes for services and funding are simply not warranted. Overlap is the rule not the exception. My view is that a conceptual split between neurodevelopmental and mental health conditions is helpful, but that a clear-cut separation when it comes to service provision and funding support is not.