Polysomnographic characteristics of bipolar hypomanic patients: Comparison with unipolar depressed patients.

Background: Sleep profile in bipolar disorder has received little attention in comparison to sleep studies in major depressive disorders. Specific sleep abnormalities especially in REM sleep parameters have been detected in depression. The current study aimed at investigating whether bipolar disorder shares the same polysomnographic (PSG) changes or not.

Methods: All night polysomnographic assessments were made for 20 patients diagnosed to have hypomania, in addition to 20 patients with major depression and 20 healthy matched controls. All participants were examined using Standardized Sleep Questionnaire, SCID-I for psychiatric diagnosis, based on DSM-IV criteria, YMRS (for hypomanic patients), HAMD (for major depression patients), and all-night polysomnography (for all subjects).

Results: The two patient groups differed significantly from controls in their sleep profile, especially regarding sleep continuity measures, Short REML (Rapid Eye Movement Latency), with increased REMD (Rapid Eye Movement sleep density). High similarity was found in EEG sleep profile of the two patient groups, though the changes were more robust in patients with depression

Limitations: A relatively small sample size, the absence of follow up assessment, lack of consideration of other variables like body mass index, nicotine and caffeine intake.

Conclusion: Similarity in EEG sleep profile between Bipolar disorder patients and patients with major depression suggests a common biological origin for both conditions, with the difference being "quantitative" rather than "qualitative". This quantitative difference in sleep efficiency and SWS (Slow wave sleep), being higher in hypomania, might explain the rather "refreshing" nature of sleep in hypomanic patients, compared to depression.