Electroencephalographic sleep profiles in single-episode and recurrent unipolar forms of major depression: II. Comparison during remission.

BACKGROUND: Previous studies indicate that recurrent forms of depression are associated with greater biological disturbances as compared to single-episode cases. This study examines whether the observed differences in the sleep patterns during recurrent and single-episode depression persist into remission following nonpharmacologic treatment.
METHODS: Two groups of patients (27 single episode [SE] and 53 recurrent unipolar [RU]) with major depression underwent sleep studies before and after nonpharmacologic treatment. Groups were equated for age, severity, and proportion of men and women. Groups were compared using multivariate analyses of covariance and/or analyses of covariance to examine six sets of sleep measures.
RESULTS: The differences observed between the SE and RU groups during the index episode persisted into early remission. The findings of greater disturbances of sleep continuity, rapid eye movement sleep and diminished slow wave sleep in the RU group supports the hypothesis that recurrent depression is associated with a more severe neurophysiological substrate than clinically comparable SE cases.
CONCLUSIONS: Although these observations are consistent with an illness progression model, the possibility that recurrent affective illness is associated with a more virulent, stable phenotype cannot be ruled out. Resolution of this issue requires longitudinal and family studies.