Cognition in older adults with bipolar disorder versus major depressive disorder

Objectives: Bipolar disorder (BD) and major depressive disorder (MDD) are associated with cognitive dysfunction in older age during both acute mood episodes and remitted states. The purpose of this study was to investigate for the first time the similarities and differences in the cognitive function of older adults with BD and MDD that may shed light on mechanisms of cognitive decline. Methods: A total of 165 subjects with BD (n = 43) or MDD (n = 122), ages 65 years [mean (SD) 74.2 (6.2)], were assessed when euthymic, using comprehensive measures of cognitive function and cognitive-instrumental activities of daily living (C-IADLs). Test results were standardized using a group of mentally healthy individuals (n = 92) of comparable age and education level. Results: Subjects with BD and MDD were impaired across all cognitive domains compared with controls, most prominently in Information Processing Speed / Executive Function. Despite the protective effects of having higher education and lower vascular burden, BD subjects were more impaired across all cognitive domains compared with MDD subjects. Subjects with BD and MDD did not differ significantly in C-IADLs. Conclusion: In older age, patients with BD have worse overall cognitive function than patients with MDD. Our findings suggest that factors intrinsic to BD appear to be related to cognitive deterioration and support the understanding that BD is associated with cognitive decline.