Abstract
Cross-sectional studies have found impaired cognitive functioning in patients with bipolar disorder, but long-term longitudinal studies are scarce. The aims of this study were to examine the 6-year longitudinal course of cognitive functioning in patients with bipolar disorder and healthy controls. Subsets of patients were examined to investigate possible differences in cognitive trajectories. Patients with bipolar I disorder (n = 44) or bipolar II disorder (n = 28) and healthy controls (n = 59) were tested with a comprehensive cognitive test battery at baseline and retested after 6 years. We conducted repeated measures ANCOVAs with group as a between-subject factor and tested the significance of group and time interaction. By and large, the change in cognitive functioning between baseline and follow-up did not differ significantly between participants with bipolar disorder and healthy controls. Comparing subsets of patients, for example those with bipolar I and II disorder and those with and without manic episodes during follow-up, did not reveal subgroups more vulnerable to cognitive decline. Cognitive performance remained stable in patients with bipolar disorder over a 6-year period and evolved similarly to healthy controls. These findings argue against the notion of a general progressive decline in cognitive functioning in bipolar disorder.
Highlights
Cross-sectional studies have found impaired cognitive functioning in patients with bipolar disorder, but long-term longitudinal studies are scarce
Cognitive performance remained stable in patients with bipolar disorder over a 6-year period and evolved to healthy controls
These findings argue against the notion of a general progressive decline in cognitive functioning in bipolar disorder
Summary
Patients with bipolar disorder show cognitive impairment relative to healthy controls at the group level.[1,2,3,4] the first systematic review that determined the prevalence of cognitive impairment in euthymic adults with bipolar disorder found large variation in the proportion of clinically relevant cognitive impairment across studies: the prevalence of impairment (5th per centile threshold) ranged from 5 to 58% depending on cognitive domain.[4]. Cross-sectional studies have reported that subsets of patients with bipolar disorder feature clinically significant cognitive impairment whereas others perform within the normal range.[14,15,16,17] It has been argued that overall group differences are driven by a subgroup of patients with marked levels of impairment.[4] We have previously found that manic episodes predict decreased grey matter volume in dorsolateral prefrontal cortex at follow-up.[18] We have reported baseline findings from our study showing that the majority of patients with bipolar disorder perform on a par with healthy controls, and patients with bipolar I and II disorder perform ,[3] a subgroup (30%) showed memory impairments.[17] It is not known whether this cognitive subgroup or bipolar subtypes show a different long-term cognitive trajectory.[8]
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