Meta-analysis of neuropsychological functioning in euthymic bipolar disorder: an update and investigation of moderator variables

Abstract

Cognitive impairment is frequently observed among individuals with bipolar disorder during acute and euthymic phases of the illness. The purpose of this study was to provide an updated meta-analysis on the neuropsychological functioning of euthymic bipolar disorder individuals and to explore study design, demographic, and clinical variables that could moderate observed effects. Searches were conducted on Medline and PsychInfo databases and 28 studies were selected that met inclusion criteria. A total of 28 cognitive variables were examined in the meta-analysis. The effects of four continuous (age, percent female, education, and illness duration) and two dichotomous (clinical course and diagnostic rigor) moderator variables were explored. Compared to controls, euthymic bipolar disorder individuals demonstrated impaired neuropsychological functioning across almost all domains, with medium-large effect sizes. Notably, vocabulary and word reading did not differ from controls. Sex did not impact neuropsychological functioning, and neuropsychological impairment decreased as education increased. Contrary to expectations, age and illness duration were negatively correlated with cognitive impairment. Diagnostic rigor of euthymia did not appear to impact effect sizes; however, clinical course received some tentative support as a moderator variable. Current results suggest that generalized, rather than specific, cognitive impairment characterizes euthymic bipolar disorder. Age, illness duration, education, and clinical course may moderate these broad cognitive effects. Against this general impairment backdrop, there may be a relative preservation of crystallized verbal ability.