Prevalence and correlates of cognitive impairment in euthymic adults with bipolar disorder: A systematic review

Background: Previous reviews have identified medium-large group differences in cognitive performance in adults with bipolar disorder (BD) compared to healthy peers, but the proportion with clinically relevant cognitive impairment has not yet been established. This review aimed to quantify the prevalence of cognitive impairment in euthymic adults with BD, and to describe sociodemographic, clinical and other factors that are significantly associated with cognitive impairment.

Methods: Systematic literature review. The population was euthymic community-dwelling adults with BD, aged 18-70 years, and recruited consecutively or randomly. The outcome was cognitive impairment, relative to healthy population norms. Electronic databases and reference lists of relevant articles were searched, and authors were contacted. Original cross-sectional studies published in peer-reviewed English-language journals from January 1994 to February 2015 were included. Methodological bias and reporting bias were assessed using standard tools. A narrative synthesis is presented together with tables and forest plots.

Results: Thirty articles were included, of which 15 contributed prevalence data. At the 5th percentile impairment threshold, prevalence ranges were: executive function 5.3-57.7%; attention/working memory 9.6-51.9%; speed/reaction time 23.3-44.2%; verbal memory 8.2-42.1%; visual memory 11.5-32.9%. More severe or longstanding illness and antipsychotic medication were associated with greater cognitive impairment.

Limitations: The synthesis was limited by heterogeneity in cognitive measures and impairment thresholds, precluding meta-analysis.

Conclusions: Cognitive impairment affects a substantial proportion of euthymic adults with BD. Future research with more consistent measurement and reporting will facilitate an improved understanding of cognitive impairment burden in BD.