How can Continuous Performance Test help to assess inattention when mood and ADHD symptoms coexist?

Depression and attention-deficit/hyperactivity disorder (ADHD) are prevalent, and often comorbid, disorders, with varying severity levels among patients. Inattention is a symptom present in both disorders, which often makes their differential diagnosis difficult in clinical practice (depression only versus comorbidity). This study aimed to investigate the influence of depressive symptoms on attention performance using one of the most common tasks in clinical practice, the continuous performance test (CPT). Ninety-three college students (60 men, 33 women) with a mean age of 24 years old were investigated with self-reports and semi-structured interviews for ADHD; the Beck Depression Inventory (BDI) was used for depression ratings. Attention measures were derived from the CPT. There was no correlation between depression and ADHD symptoms; in addition, depression was not correlated with any of the CPT scores; ADHD symptomatology was the only predictor of changes in those CPT variables (commission and omission errors and d prime). ADHD-associated impairment on the CPT was not augmented by the presence of depressive symptoms, making neuropsychological results on this test helpful for the differential diagnosis. When attention deficits are observed in individuals with mild or moderate depression, they are most likely not attributed to depression.