[Speed of onset of depressive episodes: a clinical criterion helpful for separating uni- from bipolar affective disorders].

Objective: Depressive episodes can begin abruptly or start very slowly (over weeks). This relevant clinical feature of affective disorders has not been systematically investigated so far. The aim of this study was to analyze speed of onset of depressive episodes in patients with unipolar depression (UD) and bipolar affective disorders (BD).

Methods: 158 adult patients with UD (N = 108) and BD (N = 50) were examined using the structured "Onset-of-Depression Inventory". Only patients without acute critical life events preceding the onset were included in the study.

Results: There was a significant positive correlation between speed of onset of the present and that of the preceding depressive episode (rho = 0.66; p < 0.001). The association between speed of onset and speed of decay of depressive episodes failed to be significant (rho = 0.20; p = 0.09). Patients with bipolar disorder were found to develop depressive episodes significantly faster than patients with major depression (p < 0.001): Whereas depressive episodes started in 58% of patients with bipolar disorder within one week, this was only the case in 7.4% of patients with major depression.

Conclusions: Within subjects, the speed of onset of depression is similar across different episodes. In the absence of acute critical life events, rapid onset of depressive episodes (within one week) is typical for bipolar depression, but not for unipolar depression. A rapid onset of depressive episodes might point to BD in patients with solely depressive episodes in the past and to subgroups with different neurobiological pathogenetic mechanisms.