[Severe depression: recurrence and chronicity]

This review paper deals with the question of the relationships between clinical severity of depression, recurrence risk and chronicity risk. About 60% of the subjects with a first episode of major depression will present a second episode lifetime. The risk of recurrence increases slightly with the severity of the index episode. Conversely, depression severity tends to be slightly higher in recurrent episodes as compared with first episodes. This is supported by a few studies of consecutive episodes within the same patients but it could also result from a selection effect. The risk that a depressive episode is still meeting the criteria of a major depressive episode two years after onset is between 10 and 20%. Neither the severity of the index episode nor its recurrent character clearly increases the risk of its chronic evolution. Finally, minor depression (as a dysthymic disorder or residual symptoms) increases the risk of a new major depressive episode. We may conclude that there are only moderate interactions between the clinical severity of depression and the risks of chronicity and recurrence. Worsening of one of these three variables will not result into a dramatic worsening of the two others. In fact, chronicity and recurrence do not specifically contribute to the severity of the next episode, they only contribute to the long-term severity of depressive disorders, which is already by itself a major issue.