Sleep Problems in Euthymic Bipolar Disorders: A Review of Clinical Studies

Sleep disturbance is of considerable interest to researchers in bipolar disorders (BD) and clinicians are increasingly aware of the impact of sleep disruptions on the course of BD (prediction of relapse) and treatment selection (sleep problems are frequently medication-refractory). The aim of this paper is to synthesize the data on the nature and prevalence of sleep problems in euthymia as observed by clinicians and reported by their patients and to explore the potential influence of study design on research findings in BD. A literature search identified 11 publications that included (i) euthymic cases and (ii) reported the prevalence of self-or observer-rated sleep problems. Study samples included from 20 to >700 euthymic BD cases, and about 60% of studies included a comparison group. Broadly conceptualized 'sleep problems' were reported in >50% of the BD cases on average, but specifically defined sleep disorders such as insomnia were reported in about 20% BD cases. This review highlights that sleep disturbances are a major clinical issue in BD even in individuals who are currently euthymic. The reported rates of insomnia and hypersomnia may indicate disturbances in the arousal or circadian systems may be key factors in increasing the rates of sleep difficulties. However, there were only a few high quality clinical studies that report self-or observer-rated prevalence data, and so developing consensus on definitions of different sleep problems in BD or greater application of the criteria used in sleep and circadian rhythm research would be potentially useful steps to allow greater cross-study comparisons of findings.