Two-year course of cognitive function and instrumental activities of daily living in older adults with bipolar disorder: evidence for neuroprogression?

Background. While bipolar disorder (BD) is a leading cause of disability, and an important contributor to disability in BD is cognitive impairment, there is little systematic research on the longitudinal course of cognitive function and instrumental activities of daily living (IADLs) in late-life. In this report, we characterize the 2-year course of cognitive function and IADLs in older adults with BD. Method. We recruited non-demented individuals 50 years and older with BD I or BD II (n=47) from out-patient clinics or treatment studies at the University of Pittsburgh. Comparator subjects ('controls') were 22 individuals of comparable age and education with no psychiatric or neurologic history, but similar levels of cardiovascular disease. We assessed cognitive function and IADLs at baseline, 1- and 2-year time-points. The neuropsychological evaluation comprised 21 well-established and validated tests assessing multiple cognitive domains. We assessed IADLs using a criterion-referenced, performance-based instrument. We employed repeated-measures mixed-effects linear models to examine trajectory of cognitive function. We employed non-parametric tests for analysis of IADLs. Results. The BD group displayed worse cognitive function in all domains and worse IADL performance than the comparator group at baseline and over follow-up. Global cognitive function and IADLs were correlated at all time-points. The BD group did not exhibit accelerated cognitive decline over 2 years. Conclusions. Over 2 years, cognitive impairment and associated functional disability of older adults with BD appear to be due to long-standing neuroprogressive processes compounded by normal cognitive aging rather than accelerated cognitive loss in old age.