ADHD Rarely Comes Alone, and Why That Guides Treatment

What the review found

A child who has ADHD and one other diagnosis is what a clinic ordinarily sees. Somewhere between 60 and 100 percent of children with ADHD also exhibit one or more comorbid disorders that often continue into adulthood. That estimate comes from a 2019 review of the comorbidity literature in the World Journal of Clinical Cases, written by Sundar Gnanavel and three colleagues working in NHS trusts in Durham and Newcastle and at Patan Academy of Health Sciences in Nepal.

The review is a narrative one. Its four authors read across sixty references and summarised them, without stating the search strategy, the inclusion criteria, or the appraisal of study quality that a systematic review requires. The method shows in the width of the ranges. Learning disorders are reported in anywhere from 10 to 92 percent of children with ADHD, a spread that describes how differently the studies were conducted at least as much as it describes children.

Read with that caution, the individual figures still converge on a picture. ADHD affects 5 to 8 percent of school children. Major depression is reported in 12 to 50 percent of young people with ADHD, more than five times the rate among young people without it, and the depression typically begins several years after the attention difficulties do. Anxiety symptoms are reported in 15 to 35 percent, and 30 to 50 percent of children with ADHD also meet criteria for conduct disorder or oppositional defiant disorder. Figures drawn from clinics run higher than figures drawn from communities, because the children who reach a specialist carry more.

The review gives anxiety a particular role. Anxiety in ADHD may partially inhibit the impulsivity and response inhibition deficits, may make working memory deficits worse, and may be qualitatively different from anxiety occurring on its own.

That role has a consequence for treatment, which the review reports at second hand from the Multimodal Treatment of ADHD study. Children who had both ADHD and an anxiety disorder were, in that trial, particularly responsive to behavioural therapy, more so than the other comorbidity groups. Children who had ADHD, anxiety, and oppositional defiant or conduct disorder responded preferentially to medication and behavioural therapy combined. For children with ADHD alone, and for those with ADHD and oppositional defiant or conduct disorder, behavioural intervention in isolation did not appear beneficial.

What it means for you and your child

A second diagnosis usually arrives as an escalation. One condition felt like something you could learn, and now the report names two, and the arithmetic seems to point somewhere frightening. The prevalence figures argue against that arithmetic. An ADHD standing entirely on its own is the less common presentation, and clinicians who work with these children expect to find something beside it.

The second condition also carries information that the first one does not. In the MTA results as this review describes them, anxiety predicted which children gained from behavioural therapy, and the presence of oppositional or conduct problems predicted that the same therapy, offered alone, would not help. A child with ADHD and worry and a child with ADHD and defiance are poorly served by the same plan, and the difference between them is legible in advance.

On bipolar disorder, the condition parents most often fear a second label predicts, the review is unusually direct, stating that a clinical diagnosis of ADHD is not a reliable antecedent in the developmental trajectory toward bipolar disorder, and that the association between the two appears more co-incidental than causal. Several studies cited in the review also suggest that ADHD with a comorbid condition may not be a distinct phenotype of its own, since the interaction of the two did not predict core deficits such as executive function beyond the independent effects of each. Two diagnoses in one child describe two conditions to work with, each behaving much as it behaves alone.

None of this promises that naming a second condition will make a treatment succeed. The evidence for the treatment claim is one trial’s result reported second hand, inside a review whose ranges are too wide to settle any prevalence question, and the authors themselves note that mixing parent, teacher, clinician and self-report accounts can inflate a comorbidity rate as easily as hide it. What survives all of that is modest and worth having. A fuller description of a child changes the list of things worth trying for that child.

The word on the report that seemed to make everything harder is the word most likely to narrow what gets tried first. Your child is in the majority.