Longitudinal Course of Cognitive Deficits in Bipolar Disorder: a Meta-analytic Study

Objective: Persistent cognitive deficits in bipolar disorder represent a major impediment to functional adjustment, but their static or progressive nature remains to be ascertained. The aim of this study was to synthesize findings from longitudinal research in order to examine the trajectory of cognitive impairment in bipolar disorder.

Method: A literature search was conducted through online databases covering the period between January 1990 and February 2014. Two approaches were undertaken. First, the results of longitudinal studies including neuropsychological assessment of stable bipolar patients at baseline and after a follow-up period of at least one year were meta-analyzed so as to obtain overall test-retest effect sizes for neurocognitive domains. Second, meta-analysis was restricted to longitudinal studies of bipolar patients including a control group. Patients' and controls' overall test-retest effect sizes were compared.

Results: Bipolar patients' performance on 14 cognitive measures remained stable after a mean follow-up period of 4.62 years. When meta-analysis was restricted to controlled studies, no patient-control differences were found regarding longitudinal cognitive outcomes.

Limitations: Test-retest differences for medication variables and mood state could not be controlled. Sufficient data were not available to investigate a wider array of neuropsychological domains. Furthermore, most primary studies included relatively short test-restest intervals.

Conclusion: To date, the available evidence from longitudinal studies is not in accordance with the hypothesis of a progressive nature of cognitive deficits in BD. The implications of this finding for further research are discussed.