Objective: Patients with bipolar disorder often report depressive symptoms that do not meet the DSM-IV criteria for an episode. Using daily self-reported mood ratings, we studied how changing the length requirement to that typical of recurrent brief depression (2-4 days) would impact the number of depressed episodes.
Method: 203 patients (135 bipolar I and 68 bipolar II by DSM-IV criteria) recorded mood daily using ChronoRecord software on a home computer (30,348 total days; mean 150 days). Episodes of depression and days of depression outside of episodes were determined. Symptom intensity (mild versus moderate or severe) was investigated within and outside of depressive episodes.
Results: Decreasing the minimum duration criterion for an episode of depression to 2 days increased the number of patients with a depressed episode two and a half times (52 to 131), and quadrupled both the number of depressed episodes per patient (0.62 to 2.88) and the number of depressed episodes for all patients (125 to 584). With a 2-day episode length, 34% of days of depression remained outside an episode. The ratio of days with severe symptoms within episodes remained consistent (about 25%) in spite of decreasing the episode length to 2 days. Considering only days with severe symptoms, about 25% remained outside of episodes even with a 2-day length. None of the results distinguished bipolar I from bipolar II disorder.
Limitations: Self-reported data, computer access required, relatively short study length, no control group.
Conclusion: Brief depressive episodes and single days of depression outside of episodes occur frequently in both bipolar I and bipolar II disorder. Moderate or severe symptoms occur during brief episodes at a ratio similar to that for episodes that meet the DSM-IV criteria.