The rate of co-occurrence of ADHD and OCD has been reported to be as high as 60%. A question persists, however, on whether ADHD-OCD comorbidity is a true entity or whether symptoms attributed to one may be facets of a phenotype of the other.
The rate of co-occurrence of ADHD and OCD has been reported to be as high as 60%.1 A question persists, however, on whether ADHD-OCD comorbidity is a true entity or whether symptoms attributed to one may be facets of a phenotype of the other. Abramovitch and colleagues2 argue that ADHD-like symptoms can manifest in persons with OCD and that this phenomenon is being misdiagnosed as comorbid ADHD-OCD. To clarify the issue, the researchers performed a systematic review of the scientific literature.
The team searched 33 years’ worth of medical literature, excluding articles that were not in English, did not base diagnoses on measures dictated by the Diagnostic and Statistical Manual of Mental Disorders, and did not provide data on ADHD-OCD co-occurrence. Forty-eight studies met inclusion criteria, representing 43 pediatric samples and 14 adult samples.
The researchers found that ADHD-OCD co-occurrence rates are highly inconsistent, ranging from 0% to 60%, particularly in pediatric studies. Most of the studies examined clinical samples although the reliable barometer for determining prevalence is nonreferred or general population samples. The wide variance was specifically seen in studies that focused on ADHD symptoms in OCD, whereas occurrence rates for studies examining OCD symptoms in ADHD (most performed in general population samples) were 3% to 7.5%. The research team, therefore, argued that a selection bias may be at play in a good deal of the scientific literature on ADHD-OCD co-occurrence.
How ADHD and OCD can co-occur is confounding, and some say that the disorders are polar opposites. ADHD is an externalizing disorder associated with impulsiveness and risk-taking behavior, mediated by dopaminergic neurochemistry. OCD, on the other hand, is an internalizing disorder associated with risk avoidance and restraint, neurochemically mediated by serotonin. Patients with OCD display frontostriatal hyperactivation whereas those with ADHD display frontostriatal hypoactivation.
The research team pointed out, however, that OCD in pediatric patients may differ neurologically from OCD in adolescents and adults. Whereas frontostriatal hypermetabolism may be present in adults with OCD, it is not in young children with OCD. In contrast to adolescent and adult OCD, pediatric OCD may be associated with decreased frontostriatal activity, which is associated with impulsive behavior as seen in ADHD. Thus, young patients with OCD may display symptoms that potentially lead to misdiagnosis of ADHD, in turn leading to inflated rates of ADHD-OCD comorbidity.
In addition, the researchers suggested that ADHD-like symptoms in patients with OCD may be attributable to executive function overload caused by obsessive rumination. Consequent neuropsychological deficits shared by ADHD can then be mistaken for ADHD, they say.
Finally, they comment that more accurate studies are sorely needed to better explain why and whether ADHD and OCD co-occur. They point out that misdiagnosis of ADHD in OCD can be particularly problematic, as stimulant therapy can significantly exacerbate OCD symptoms.
1. Abramovitch A, Dar R, Mittelman A, Schweiger A. Don't judge a book by its cover: ADHD-like symptoms in obsessive-compulsive disorder. J Obsessive Compuls Relat Disord. 2013;2:53-61.
2. Abramovitch A, Dar R, Mittelman A, Wilhelm S. Comorbidity between attention deficit/hyperactivity disorder and obsessive-compulsive disorder across the lifespan: a systematic and critical review. Harv Rev Psychiatry. 2015 Jun 6. [Epub ahead of print]