There is growing evidence that ASD and ADHD share common genetic variants, similar psychological deficits and neuroimaging differences. Perhaps it is time to put the term ‘neurodevelopmental disorders’ into the history books as well? We believe so, and we’ve coined the term ADHtism to better talk about this complex profile.
Adapted and edited by Peter Vang, ADDspeaker.org (2020)
The term ‘neurodevelopmental disorders’ has a long history, yet it had not been included in previous editions of the ICD or the DSM.
The term applies to a group of disorders of early onset that affect both cognitive and social communicative development, are multi-factorial in origin, display important sex differences where males are more commonly affected than females, and have a chronic course with impairment generally lasting into adulthood.
The term distinguishes these disorders from other more common disorders of childhood, such as anxiety and mood disorders, which were thought to arise from some type of psychosocial adversity and have a more episodic course.
In the ICD-11, the category ‘neurodevelopmental disorders’ includes;
(1) disorders of intellectual development,
(2) developmental speech or language disorders,
(3) autism spectrum disorders (ASD),
(4) developmental learning disorders,
(5) developmental motor coordination disorder,
(6) attention deficit hyperactivity disorder (ADHD),
(7) stereotyped movement disorder, and
(8) a remainder category labeled ‘other neurodevelopmental disorders’.
What’s new in ICD-11?
There are a number of very important departures from the ICD-10, which are consistent with recent literature and follow, in spirit, the changes from the DSM-IV to the DSM-5.
First, the ICD-10 does not have a specific grouping for neurodevelopmental disorders and uses slightly different terminology for the specific conditions that have been included within it — ‘mental retardation’, ‘disorders of psychological development’, and ‘pervasive developmental disorder’ are the terms used instead.
Second, hyperkinetic disorder (now termed ‘attention deficit hyperactivity disorder’ in ICD-11) appears under the ICD-10 category of ‘behavioral and emotional disorders with onset in childhood or adolescence’.
Third, it is notable that, in the ICD-10, pervasive developmental disorder is exclusionary for hyperkinetic disorder, a stipulation that is no longer present in the ICD-11. Now, in the ICD-11, both ASD and ADHD may co-exist in the same individual. The age of onset for ASD is now in the early developmental period rather than being specified as having an onset by 3 years of age.
Other major changes include the fact that the eight different pervasive developmental disorders in the ICD-10, including childhood autism, atypical autism and Asperger syndrome, have disappeared entirely and are now grouped together under one category, namely ASD. This is a notable change that still arouses some controversy.
Several systematic reviews have found that the distinctions between these subtypes appear to be of dubious diagnostic validity or to represent quantitative rather than qualitative variation.
In both the DSM-5 and the ICD-11, grouping all these individuals together is now accompanied by adding different ‘specifiers’ to the ASD diagnosis in an attempt to take account of the enormous heterogeneity inherent in the disorder’s presentation.
These specifiers include intellectual level, language level, medical or genetic comorbidities, and mental health comorbidities.
NOTE: ADHtism is a term we’ve coined here at ADDspeaker, so as to better talk about the combined symptomatology of ADHD and Autism, as our real life experience shows, that more than 50% of all who have been diagnosed with,one,or,the other, also present symptoms of the other, thereby making it even more complex to accurately diagnose. It is NOT a valid clinical term used officially…yet …
While there is general support for ‘lumping’ the ASDs rather than ‘splitting’ them, there has been little or no research on the clinical utility of these specifiers nor on whether these are the ‘right’ specifiers.
It is to be hoped that this conceptualization of a single disorder with multiple specifiers will foster a new generation of studies that attempts to consider the remarkable heterogeneity seen in ASD both between individuals with ASD but also within the same person with ASD over time.
The recognition that ADHD and ASD can coexist is also an important refinement that is extremely useful since there is good evidence that ASD individuals with concurrent ADHD can benefit from stimulant medications.
There is also growing evidence that ASD and ADHD share common genetic variants, similar psychological deficits and neuroimaging differences.
Nevertheless, despite the term ‘neurodevelopmental disorders’ now being official, it could be argued that the designation has outlived its usefulness — the various conditions contained under this grouping differ from each other (from severe ASD to mild coordination disorder) such that they have little in common.
Therefore, the allocation of treatment interventions and prognosis cannot be generalized from one neurodevelopmental disorder to another. If clinical utility is the prime criterion for the added value of diagnostic terms, then ‘neurodevelopmental disorders’ as a meta-term appears to make a minimal contribution.
Moreover, it could also be argued that all disorders with onset in childhood or adolescence are neurodevelopmental disorders. Schizophrenia, mood (including bipolar), and anxiety disorders are all brain-based disorders.
They have also, on occasion, been referred to as neurodevelopmental disorders, especially schizophrenia, as they involve difficulties in the execution of intellectual, motor, language, or social functions as well as other domains that arise from alterations in brain circuits.
Similar to the definition of neurodevelopmental disorders in the ICD-11, the presumptive etiology of mood disorders in childhood and adolescence, for example, is also ‘complex’ and is thought to arise from ‘physical’ processes (inflammatory processes, chronic sleep disturbance, possibly the microbiome) and genetic factors as well as from various types of stressful life events.
The growing awareness of the comorbidity of mood and anxiety disorders with various neurodevelopmental disorders (once the children reach adolescence) is another indication that the boundary between neurodevelopmental and non-neurodevelopmental disorders in the ICD-11 is ambiguous.
In other words, what does not constitute a neurodevelopmental disorder among disorders that arise in childhood and adolescence?
More importantly, what is the clinical utility of grouping them together and separating them from disruptive behaviour and internalizing disorders?
It is possible that mood and anxiety disorders are more closely associated with psychosocial adversity than with neurodevelopmental disorders; however, surely these are quantitative rather than qualitative differences.
Furthermore, so many evidence gaps remain in our understanding of etiology and pathogenesis that to build the foundation of a classification system on unknown and assuredly complex aetiological factors is a fragile enterprise.
The term represents child and adolescent psychiatry’s version of the old ‘functional’ versus ‘organic’ distinction that has long been done away with in adult psychiatry following remarkable advances in neuroscience.
Perhaps it is time to put the term ‘neurodevelopmental disorders’ into the history books as well?
Stein, D.J., Szatmari, P., Gaebel, W. et al. Mental, behavioral and neurodevelopmental disorders in the ICD-11: an international perspective on key changes and controversies. BMC Med 18, 21 (2020). https://doi.org/10.1186/s12916-020-1495-2