Background: In patients with affective disorders, the full-blown symptomatology of a depressive episode can develop very fast (e.g., within 1 d) or slowly over weeks or months. These differences in the speed of onset of depression are likely to reflect stable intraindividual differences in neurobiological pathomechanisms. This article presents available data on this issue from published studies and from a recently unpublished study and discusses the relevance of these data for diagnostic, therapeutic, and research purposes.
Methods: On the basis a database search, we reviewed the literature on speed of onset of depressive episodes. Results of a study for which only some of the data have previously been published involving 205 patients with unipolar or bipolar depression were also considered.
Results: Five older studies produced data concerning the speed of onset of depressive episodes. In addition, our research group has conducted 2 other more recent studies that used the Onset of Depression Inventory to assess the speed of onset of depressive episodes. The major findings of the studies we examined were that depression developed within 1 week in 50% to 58% of patients with a bipolar disorder, whereas only in 7.4% to 21.4% of those with unipolar depression. Different depressive episodes appeared to develop at a similar speed within individual subjects (correlation coefficients: 0.46 to 0.66).
Conclusions: Consistent evidence from 2 studies that used the Onset of Depression Inventory revealed that rapid onset of a depressive episode is more common in patients with bipolar disorder than in those with unipolar major depressive disorder and may be an indication of a latent, not yet expressed, bipolar disorder. The neurobiology of the speed of onset of depressive episodes is a topic for future research.