A meta-analysis of cognitive deficits in euthymic patients with bipolar disorder

BackgroundA number of studies have reported evidence of cognitive deficits in euthymic bipolar patients. Qualitative reviews of the literature have indicated impairments in executive functions and declarative memory are most consistently reported. However, not all primary studies conducted to date have had sufficient power to detect statistically significant differences and there have been few attempts to quantify the magnitude of impairments. This review aims to combine data from available studies to identify the profile of neuropsychological deficits in euthymic bipolar patients and quantify their magnitude.MethodSystematic literature review and meta-analysis.ResultsLarge effect sizes (d ≥ 0.8) were noted for aspects of executive function (category fluency, mental manipulation) and verbal learning. Medium effect sizes (0.5 ≤ d < 0.8) were found for aspects of immediate and delayed verbal memory, abstraction and set-shifting, sustained attention, response inhibition, and psychomotor speed. Small effect sizes (0.2 ≤ d < 0.5) were reported for verbal fluency by letter, immediate memory, and sustained attention.LimitationsSufficient data were not available to investigate all domains. For example analyses did not include measures of visuospatial function.ConclusionEuthymic bipolar patients demonstrate relatively marked impairment in aspects of executive function and verbal memory. It is not yet clear whether these are two discrete areas of impairment or are related to one another. Future investigations should clarify the functional significance of deficits and indicate whether patients will benefit from ameliorative interventions.