Impaired cognitive flexibility in patients with attention deficit hyperactivity disorder (ADHD) may be entirely due to the presence of comorbid bipolar disorder, say researchers.
The team found that 51 ADHD patients who also had bipolar disorder had significantly poorer results on the Wisconsin Card Sorting Test (WCST) than 278 patients who had ADHD alone.
“Overall, our current and previous findings on ADHD–[bipolar disorder] comorbidity point to a scenario where ADHD is mostly associated with inhibitory control impairments, and [bipolar disorder] with set-shifting problems,” say study author Claiton Bau (Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil) and co-workers.
Patients with comorbid bipolar disorder achieved an average of 86.1 correct answers on the WCST. Those with ADHD alone managed 93.7 correct answers, which did not significantly differ from the average of 94.3 correct answers achieved by 91 mentally healthy controls.
Likewise, ADHD patients with bipolar disorder made more total errors than those without, at 41.9 versus 34.3, and more non-perseverative errors, at 22.2 versus 16.7, although their scores did not differ for perseverative errors and perseverative responses. Patients with bipolar disorders also completed significantly fewer categories than those with ADHD alone, at 5.3 versus 6.4.
Other comorbidities, including depressive, anxiety, panic, and substance abuse disorders, were not significantly associated with patients’ scores on the WCST.
“The neuropsychological evaluation of executive functions in ADHD should thus consider the presence or absence of comorbid [bipolar disorder],” write the researchers in Bipolar Disorders.
They stress the importance of detailed neurocognitive evaluation, since comorbid psychiatric disorders appear to influence specific aspects of executive function, which, in turn, “ imply poorer psychosocial functioning.”
The team says: “Understanding the specific impairments attributable to ADHD or [bipolar disorder] might improve differential diagnosis and lead to new studies on the development of appropriate interventions.”
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