Cognitive Deficits in Euthymic Patients With Bipolar Disorder: State or Trait Marker?

Cognitive deficits have been demonstrated in people in the euthymic phase of bipolar disorder. This cross-sectional study compared euthymic bipolar disorder patients (n = 30) with never psychiatrically ill controls (n = 30) on a neuropsychological test battery containing tasks of executive function, the Wisconsin Card Sorting Test (WCST), attention and working memory, digits forward and backward, and speed of information processing digit symbol. Scores on the Mini-Mental State Examination (MMSE) and vocabulary test did not differ between the groups. The bipolar group was significantly impaired compared with controls on various indices of executive function on the WCST and on the digit tests. The impaired performance on the digit tests, but not the WCST, was significantly associated with medication status, notably prescribed benzodiazepines. There was no significant effect of severity or course of illness on performance. The findings support the hypothesis that impairments in executive function are present between illness episodes in bipolar disorder, and so they are not simply state markers.