[The long-term course of depression (epidemiology and clinical aspects)]

Depression recurs in three quarters of cases; it is therefore necessary to undertake long-term studies in order to understand the clinical and epidemiological implications. Current classifications schematically distinguish depressive episodes according to their more or less permanent and complete semiological expression (at least five symptoms over at least two weeks for a major depressive episode, versus at least two criteria for the greater part of the time over at least two years) or their time-scale (isolated or recurrent episodes; recurrent brief depressive episodes...). The terminology of therapeutic strategies is based on the temporal definitions of the depressive process. Thus one speaks of curative treatment during the acute phase of the illness (two months), maintenance treatment during recurrence (four to six months), and prophylaxis against later possible recurrences (more than six months). Epidemiological findings emphasize the importance not only of recurrence of depression (50% in the year following an index episode), but also that of becoming chronic (20%), of partial remissions (15 to 20%), and the "bipolarisation" of a unipolar illness (10 to 15%). Finally, certain risk factors for recurrence have been identified. The most important of these is a large number of previous depressive episodes.