Does comorbid bipolar disorder increase neuropsychological impairment in children and adolescents with ADHD?

To assess differences in executive functioning between children and adolescents with attention-deficit/hyperactivity disorder (ADHD) comorbid or not with bipolar disorder (BD), and to study the neuropsychological profile of subjects with the comorbidity in a clinical sample from a developing country.

Case-control study comparing 23 participants with BD + ADHD and 85 ADHD-only subjects aged 6 to 17 years old. Both groups were drug-free. Executive function domains were assessed with the Stroop Test, the Wisconsin Card Sorting Test, and the Continuous Performance Test II.

The group with juvenile BD + ADHD showed a significantly worse performance on the Stroop task, including time in color (p = 0.002), time in color-word (p < 0.001), interference, number or errors in color and color-word (p = 0.001), and number of errors in word cards (p = 0.028). No between-group differences were found in other tests.

Our findings suggest that ADHD-only and ADHD + BD do not show differences in inhibitory control and set-shifting domains. However, children and adolescents with BD and comorbid ADHD show greater impairment in processing speed and interference control. This suggests a potentially higher impairment in the dorsolateral prefrontal cortex and may be a potential neuropsychological signature of juvenile BD comorbid with ADHD.