Depressive episodes take significantly less time to develop in patients with bipolar disorder (BD) than in those with unipolar depression, German study findings confirm.
The researchers found that the duration of depressive episode onset among BD inpatients was slightly more than 1 week, compared with around 1 month in those with unipolar depression.
"Clinicians should consider the possibility of a hidden bipolarity in patients who develop a depressive episode within a few days," advise Maria Strauss and colleagues from the University of Leipzig.
The findings come from a study of 24 BD patients and 122 with unipolar depression who were aged at least 18 years and treated for a depressive episode at the team's institution. Of the unipolar depression patients, 42 had experienced their first depressive episode and 80 had recurrent depressive disorder.
The speed of depressive episode onset, defined as the duration from the first signs of depressive symptoms until manifestation of a full-blown depressive syndrome, was assessed using the Onset-of-Depression Inventory (ODI).
The researchers found that BD patients had a significantly shorter median duration of depressive episode onset than those with unipolar depression, at 8.5 versus 28.0 days.
Among patients with unipolar depression, those with recurrent depression had a significantly shorter median duration of depressive episode onset than those with a first episode, at 28.0 versus 38.5 days.
Furthermore, 50.0% of BD patients developed a full-blown depressive episode within a week of onset compared with 16.7% of first-episode depression patients and 25.0% of those with recurrent depression.
"The findings of this study confirm that the speed of onset of depressive episodes differs between BD and unipolar depression," conclude Strauss et al in the Journal of Affective Disorders.
They add: "It should be noted that the speed of depression onset is an intra-individually quite stable clinical characteristic symptom that can be used to detect bipolarity.
"Future studies should address the question whether the speed of onset assessed with the ODI is helpful to delineate subgroups of patients with affective disorders which are more homogeneous concerning their pathophysiological mechanisms, their phenotypes, genotypes and therapeutic response."
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