MedWire News: Hypersomnia among bipolar disorder (BD) patients who are in an inter-episode period may predict future depressive symptoms, results from a US study suggest.
Writing in the Journal of Affective Disorders, Allison Harvey (University of California, Berkeley) and team explain that BD patients "in the inter-episode period spend roughly 50% of their time unwell, and these symptoms predict relapse into mania or depression. Hence, there is a critical need to identify aspects of the illness that contribute to inter-episode dysfunction and to relapse."
They add: "Hypersomnia may be one candidate contributing to inter-episode dysfunction and to relapse, but is understudied in BD."
To investigate, the researchers studied 56 BD patients aged a mean of 35.6 years who were in an inter-episode period at the time of enrollment, and 55 similarly aged mentally healthy individuals.
All of the participants were assessed at baseline for possible hypersomnia using five indices: the Duke Structured Interview for Sleep Disorders (DSISD), the Inventory of Depressive Symptomatology-Self Report version (IDS-SR), the Inventory of Depressive Symptomatology-Clinical Version (IDC-C), the Beck Depression Inventory-Second Edition (BDI-II), and a 7-day sleep diary.
Each participant was interviewed approximately 6 months later and assessed for current mood status.
Among the bipolar disorder patients, mean depression score on the IDS-C at follow-up was 11.3 and the mean mania score on the Young Mania Rating Scale was 2.6.
Hypersomnia was more common in the bipolar group than in the control group according to the DSISD, IDS-SR, BDI-II, and sleep diaries regarding total sleep time, with no differences in hypersomnia prevalence found between the groups on the IDS-C, or on the sleep diary regarding time in bed.
Inter-episode prevalence estimates of hypersomnia varied from 4% to 50% in the bipolar group depending on the index used to assess it. However, convergent scores from three of the indices indicated that 25% of BD patients had inter-episode hypersomnia.
After accounting for baseline levels of depression, the researchers found that scores on the IDS-C and the BDI-II significantly predicted future depressive symptoms among the BD patients.
Differences in hypersomnia rates between BD patients who were not medicated, taking one medication, and taking more than one medication were not significant, the researchers note.
Harvey and team conclude: "This study demonstrates that hypersomnia in the inter-episode period of bipolar disorder relates to future depressive symptoms, and adds to the growing body of evidence on the importance of inter-episode symptoms predicting bipolar relapse."
They add: "Though no gold standard measure for hypersomnia currently exists, this research takes a step towards identifying a clinically and empirically useful hypersomnia assessment."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
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