Introduction: Bipolar disorder is associated with cognitive dysfunction in several domains. Medication effect is a potential confounder that can only be statistically controlled in many studies. The cognitive profile in bipolar disorder during remission on maintenance antipsychotics or mood stabilizers medication has not been compared before.
Methods: We compared the cognitive profile of bipolar disorder patients euthymic for 2 month or more on monotherapy with novel antipsychotics (AP) (n=16), lithium carbonate (Li) (n=25) or valproic acid (VPA; n=26). Forty-two individuals were assessed as controls. The cognitive battery included Wechsler Adult Intelligence Scale-Revised (WAIS-R) subtests, the Wechsler Memory Scale (WMS), and Wisconsin Card Sorting Test (WCST).
Results: All three patient groups compared to controls performed poorly on the working memory and verbal memory tasks (F=3.59, df=3, p=0.02 for WAIS-R Arithmetic and F=123.64, df=3, p<0.01 for WMS Logical Memory). The differences remained significant after controlling for age. Across patients, the only significant difference was between the Li and AP groups in terms of working memory. The Li group performed better (F=3.59, df=2, p=0.02) and the difference survived correction for age and clinical features.
Conclusions: The findings of this study suggest that working memory impairment in bipolar patients on monotherapy with atypical AP, whereas verbal memory impairment might be related to bipolar disorder itself. Working memory might be a state marker, whereas verbal memory could be a trait marker of bipolar disorder. Atypical AP might have an adverse effect on cognition in bipolar disorder. These findings cannot be generalized to all bipolar patients, particularly the poor responders to monotherapy.
Keywords: Bipolar disorder; atypical antipsychotic; euthymia; lithium; valproic acid.