Don’t judge a book by its cover: ADHD-like symptoms in obsessive compulsive disorder

Reported OCD–ADHD comorbidity rates are highly variable and the two disorders are characterized by opposite symptomatology and antithetical pathophysiology. We hypothesized that OCD-related attentional impairment could be misdiagnosed as ADHD symptoms. Thirty adults with OCD, thirty with ADHD, and thirty matched healthy controls (HC) completed disorder-specific measures and an ADHD DSM-IV based questionnaire examining childhood and current symptoms. The ADHD group met significantly more current and childhood ADHD criteria than the other groups. Within the HC and ADHD groups, but not the OCD group, significant positive correlations were found between childhood and current ADHD symptoms. Only within the OCD group, obsessive–compulsive symptoms and ADHD criteria correlated positively. These findings support the predictions of the executive overload model of OCD, suggesting that ADHD-like symptoms in OCD may be a consequence of OCD symptomatology. Clinical implications of a potential misdiagnosis should be considered in light of the probability that stimulant medication exacerbates OCD symptoms. This is particularly important in children, where ADHD diagnosis is based primarily on informant reports.

► Reported rates of adult OCD–ADHD co-occurrence are unusually inconsistent.
► OCD and ADHD are associated with antithetical phenomenology and pathophysiology.
► Manifestations of OCD-related inattention may be misdiagnosed as ADHD symptoms.
► In OCD only, current ADHD symptoms correlate with OC symptoms.
► Risk of misdiagnosis, especially in children when primarily relying on informants.