Objective: Some investigators have suggested decreasing the minimum hypomania episode length criterion from 4 days, as in the DSM-IV, to 2 days. Using daily self-reported mood ratings, we studied the impact of changing the length requirement on the number of hypomanic episodes in patients with bipolar disorder.
Method: 203 patients (135 bipolar I and 68 bipolar II by DSM-IV criteria) recorded mood daily using ChronoRecord software (30,348 total days, mean 150 days). Episodes of hypomania and days of hypomania outside of episodes were determined.
Results: Decreasing the minimum duration criterion for an episode of hypomania from 4 to 2 days doubled the mean percent of days in a hypomanic episode for each patient (4% to 8%), doubled the number of patients with a hypomanic episode (44 to 96) and increased the number of hypomanic episodes for all patients about three-fold (129 to 404). With a minimum episode length of 4 days, bipolar I patients were more likely to report hypomania outside episodes than bipolar II patients (p=0.010), but with a length of 2 or 3 days there was no significant difference in the distribution of hypomania outside of episodes by diagnosis. With a 2-day length, about one-third (36%) of hypomania remained outside of an episode.
Limitations: Self-reported data, computer access, relatively short length, fewer bipolar II than bipolar I patients.
Conclusion: As the minimum length for an episode of hypomania decreases, there was a large increase in both the number of episodes and number of patients with episodes. One-day hypomania outside of episodes occurs frequently in both bipolar I and bipolar II disorder.