Patients with bipolar disorder have been reported to have neurocognitive deficits; however, it is not known whether the cognitive dysfunctions are state-dependent or a stable trait. Lithium and valproate, 2 of the most widely used mood stabilizers in the treatment of bipolar disorder, have also been associated with cognitive impairment. However, the degree and pattern of neurocognitive impairment in euthymic bipolar patients on either monotherapy with lithium or valproate have not been compared before in depth.
We compared 17 euthymic outpatients with bipolar disorder (BD) on lithium monotherapy to 11 euthymic outpatients with BD on valproate monotherapy and 29 comparison subjects using tests measuring immediate verbal memory and executive functions in addition to 3 subtests of the Wechsler Adult Intelligence Scale Revised. The groups were similar in terms of level of education, duration and severity of illness, and gender distribution. Patients on lithium monotherapy were older than patients on valproate and healthy controls. Mood symptoms as assessed by standardized scales were mild to non-existent in both patient groups.
Immediate verbal memory was impaired in both patient groups compared to controls, where the main effect of age was not significant. No significant differences could be found on the other cognitive measures.
Both lithium and valproate may be associated with immediate verbal memory impairment, sparing other cognitive functions. Presence of a similar verbal memory deficit in the lithium and valproate groups suggests that this deficit might be intrinsic to BD or that the 2 medications influence immediate verbal memory similarly. Larger samples of remitted bipolar patients on monotherapy should be studied for more precise conclusions.