Does emotion predict the course of major depressive disorder? A review of prospective studies.

PURPOSE Emotional dysfunction is a hallmark of major depressive disorder (MDD). There has been wide interest in identifying the nature and significance of emotional deficits in MDD. Given the paramount goal of identifying etiological markers of MDD that can sharpen prevention and treatment efforts, researchers have pursued emotion as a functionally significant factor and predictor of clinical course in MDD. This review is the first to summarize the literature examining emotion as a predictor of the clinical course of MDD. METHOD We conducted a systematic review of all published studies reporting on the prospective relationship between positive and negative emotionality (PE and NE)--measured at the state or trait level--and the longitudinal course of MDD in diagnosed adults. Physiological, behavioural, and subjective indices of emotion were considered. The primary analyses encompassed 28 research reports that included data from 3,798 participants and tested a total of 60 hypotheses. RESULTS Lower levels of PE predicted poorer MDD course with some consistency. Paradoxically, both lower levels of state NE and higher levels of trait NE predicted poorer MDD course. The relationships between emotionality and MDD course generally held even after initial depression symptom severity was taken into account. CONCLUSION Emotion shows promise as a predictor of MDD course. Implications of these data for current theories of emotion and MDD, the apparently divergent relation between state and trait NE and course, and future directions to further clarify the functional significance of emotion in the context of MDD are discussed.