Onset of depressive episodes is faster in patients with bipolar versus unipolar depressive disorder: evidence from a retrospective comparative study.

OBJECTIVE

Depressive episodes can have a very fast onset (< 1 hour) or start very slowly (> 1 month). This interesting aspect, pointing to different neurophysiological pathomechanisms, has not been systematically evaluated so far. The aim of this study was to describe speed of onset of depressive episodes in a consecutive sample of patients with at least 1 depressive episode and to investigate potential differences between patients with major depression versus bipolar affective disorders concerning this variable.

METHOD

We examined 158 consecutive adult patients with major depression (N = 108) and bipolar disorder (N = 50) diagnosed according to criteria of the International Statistical Classification of Diseases, 10th revision, by applying the structured Onset-of-Depression Inventory. Patients with acute critical life events preceding the onset were excluded from final analyses. Data were collected between December 2001 and January 2007.

RESULTS

There was a significant positive association between speed of onset of the present depressive episode and that of the preceding depressive episode (rho = 0.66, p < .001). Patients with bipolar disorder developed full-blown depressive episodes significantly faster than patients with major depression (p < .001): Whereas depressive episodes began within 1 week in 58% of patients with bipolar disorder, this was the case in only 7.4% of patients with major depression.

CONCLUSION

Intraindividually, the speed of onset of depression is similar across different episodes. In the absence of acute critical life events, fast onset of depressive episodes (within 1 week) is common in bipolar disorder but rare in major depression. This aspect might be useful to identify depressive episodes occurring within a bipolar affective illness and might characterize a subgroup of patients with a distinct neurobiology.