Objective: Most patients with bipolar disorder experience depressive symptoms outside of an episode of depression as defined by DSM-IV criteria. This study explores the frequency of brief depressive episodes, lasting 1 to 4 days, using daily self-reported mood ratings.
Method: Mood ratings were obtained from 448 patients (281 bipolar I, 167 bipolar II) using ChronoRecord software (91,786 total days). Episodes of depression and days of depression outside of episodes were determined. The intensity of depressive symptoms (mild versus moderate to severe) was compared.
Results: Using the DSM-IV length criteria, 61% of all depressive days occurred outside of a depressed episode. Decreasing the minimum length criterion to 2 days, both the number of patients experiencing a depressed episode (128 to 317) and the mean percent of days spent in a depressed episode by each patient (7.9% to 17.8.%) increased by about 2½ times, and 34.3% of depressed days remained outside of an episode. Depending on the episode length, the proportion of days within an episode with severe symptoms varied from 1/3 to 1/4 for episodes lasting from 14 to 2 days, and 1/4 for single-day episodes. There was no significant difference in the frequency of brief depressive episodes between bipolar I and II disorders. For all episode lengths, patients taking antidepressants spent 4% more days within an episode and 6% more days with depressive symptoms outside of an episode than those not taking antidepressants.
Conclusion: Brief depressive episodes lasting 1 to 4 days occur frequently in bipolar disorder and do not distinguish between bipolar I and II disorders. Symptoms of moderate to severe intensity occur on 1/4 to 1/3 of the days in brief depressive episodes. This study did not address brief depression in those without bipolar disorder. Patients taking antidepressants experienced more brief depressive episodes. Controlled trials are needed to assess the impact of antidepressants on subsyndromal depressive symptoms.