Attention deficit hyperactivity disorder and comorbid disorders: issues of overlapping symptoms

OBJECTIVE: Since some symptoms are shared by both attention deficit hyperactivity disorder (ADHD) and comorbid psychiatric conditions, it is possible that a diagnosis of ADHD is an artifact of the overlapping symptoms. This article focuses on the assessment of the influence of overlapping symptoms on the diagnosis of ADHD. METHOD: Three groups of subjects were studied: a group of clinically referred children and adolescents, a group of nonreferred adults who were the parents of these children and adolescents, and a group of clinically referred adults with ADHD. The authors assessed the extent of symptom overlap between ADHD and the disorders that frequently co-occur with ADHD; major depression, bipolar disorder, and generalized anxiety disorder. To determine the degree to which this symptom overlap influences these diagnoses, each individual was rediagnosed on the basis of two different techniques that corrected for the overlapping symptoms, a subtraction method and a proportion method. RESULTS: The majority of subjects who had both ADHD and a comorbid psychiatric disorder maintained their diagnosis of ADHD when the overlapping symptoms were subtracted. Moreover, when overlapping ADHD symptoms were subtracted, on average, 79% maintained their diagnosis of major depression, 56% maintained their diagnosis of bipolar disorder, and 75% maintained their diagnosis of generalized anxiety disorder. CONCLUSIONS: These findings show that ADHD is not an artifact of symptoms shared with other psychiatric disorders and that the comorbid conditions themselves are not an artifact of overlapping ADHD symptoms.