Emergent Divergence

Autism is associated with a wide array of co-occurring conditions. In fact, it is widely discussed that Autistic people have “all the things”, meaning that we are prone to conditions that are otherwise considered rare or in some cases problematic. When talking about this topic however, one thing comes up more often than anything else. Attention Deficit Hyperactivity Disorder, or as it is better known, ADHD. This comes up so often that some have already assumed that it is a part of the autism spectrum. The truth is a little more complicated. While ADHD is very common for Autistic people (who have labelled the combination as AuDHD) it is still considered a seperate issue from that of autism. But should it be?

How common is ADHD in Autistic people?

ADHD occurs at an enormously higher rate in the Autistic population when compared to the overall global population. Rong et al (2021) put the figure at 40.2% of Autistic people, with some studies placing the figure even higher. Further meta-analysis however indicates that in the general population, only 2.58% of adults are diagnosed ADHD (Song et al, 2021), while another found that ADHD is diagnosed in 3-12 year olds and 12-18 years olds in 7.6% and 5.6% of individuals respectively (Salari et al, 2023).

There is an addendum to these figures, however. Much of the existing literature specifically looks at those diagnosed. I have explored in previous writing how almost 1.2 million people in the UK are estimated to be undiagnosed Autistic, compared to less than 450,000 diagnosed. This means that figures may be different if self-diagnosis was included (which would be prudent given the significant barriers to diagnosis in many countries), and they may also be different if diagnostic pathways were more easily accessed.

Further to this, research has indicated that when autism and ADHD occur together, it presents it’s own unique external presentation, that is observably different from both autism and ADHD when observed in isolation (Carta et al, 2020). This provides an evidence base for community anecdotes and my own experience that the two together (dubbed AuDHD in community spaces) present their own unique neurocognitive style.

French et al (2023) identified risks of impact on wellbeing, social interactions, as well as increased risk of substance use and criminality from undiagnosed ADHD and/or autism. It is clear that not only is ADHD a significant intersection in Autistic experience, but a matter of vital importance when considering outcomes for a person’s life.

Should the co-occurrence of autism and ADHD be a discrete diagnostic category?

Ask any AuDHD’er, and they will attest to the fact that their experience differs from that of people who experienced Autistic or ADHD cognition in isolation. In addition, this particular dual diagnosis presents its own set of risk factors that make it prudent to curate support beyond that which one might provide for only autism or ADHD individually.

Beyond statistics and peer-reviewed research are the community concepts that highlight distinct mechanisms for crisis situations in AuDHD’ers. In particular, I consider Adkin’s monotropic split and spiral, and the burnout to psychosis cycle. Anecdotally reports and experiences suggest these concepts are a frequent feature in AuDHD mental health, suggesting that by recognising this co-occurrence as a discrete identity we might open up academic research towards something more meaningful for this populations wellbeing.

In truth, ADHD is difficult to disambiguate from autism, and in some regard, it would almost seem to make sense to amalgamate it into a new a broader definition of the autism spectrum. However, the only thing I feel we can confidently say with the current knowledge base we have is that AuDHD, the co-occurrence of the two, presents a unique neurocognitive identity that is functionally and experientially different from autism or ADHD on their own.

References

Carta, A., Fucà, E., Guerrera, S., Napoli, E., Valeri, G., & Vicari, S. (2020). Characterization of clinical manifestations in the co-occurring phenotype of attention deficit/hyperactivity disorder and autism spectrum disorder. Frontiers in Psychology, 11, 861.

French, B., Daley, D., Groom, M., & Cassidy, S. (2023). Risks associated with undiagnosed ADHD and/or autism: A mixed-method systematic review. Journal of Attention Disorders, 27(12), 1393-1410.

Rong, Y., Yang, C. J., Jin, Y., & Wang, Y. (2021). Prevalence of attention-deficit/hyperactivity disorder in individuals with autism spectrum disorder: A meta-analysis. Research in Autism Spectrum Disorders, 83, 101759.

Salari, N., Ghasemi, H., Abdoli, N., Rahmani, A., Shiri, M. H., Hashemian, A. H., … & Mohammadi, M. (2023). The global prevalence of ADHD in children and adolescents: a systematic review and meta-analysis. Italian journal of pediatrics, 49(1), 48.

Song, P., Zha, M., Yang, Q., Zhang, Y., Li, X., & Rudan, I. (2021). The prevalence of adult attention-deficit hyperactivity disorder: A global systematic review and meta-analysis. Journal of global health, 11.