Cognitive functioning in euthymic bipolar I and bipolar II patients

There is growing evidence of cognitive impairment as a trait factor in bipolar disorder. The generalizability of this finding is limited because previous studies have either focussed exclusively on bipolar I disorder or have analysed mixed patient groups. Thus, it is still largely unknown whether bipolar II patients perform differently from bipolar I patients on measures of cognitive functioning.

A total of 65 patients with bipolar I disorder, 38 with bipolar II disorder, and 62 healthy controls participated in the study. Patients had to be euthymic for at least one month. Clinical and demographic variables were collected in a clinical interview and with the Structured Clinical Interview for DSM-IV. Cognitive functioning was assessed using a neuropsychological battery. Univariate and multivariate analyses of variance were conducted for analyzing possible differences between the groups.

The multivariate analysis of covariance (MANCOVA) indicated overall differences in neuropsychological performance between the three groups (Pillai Spur: F 1.96, p = 0.003). Post hoc comparisons revealed that patients with bipolar I disorder showed significantly lower scores in psychomotor speed, working memory, verbal learning, delayed memory, and executive functions than healthy controls. Patients with bipolar II disorder showed significant deficits in psychomotor speed, working memory, visual/constructional abilities, and executive functions compared to controls, but not on verbal learning and delayed memory. The two patient groups did not differ significantly from each other on any domain tested.

These results support a similar pattern of cognitive deficits in both subtypes of bipolar disorder.