A group of researchers are questioning the validity of the four day hypomanic threshold needed for a diagnosis of bipolar II. The four day rule could potentially exclude a considerable number of individuals with bipolar II.
They found that 186 bipolar II disorder patients who met the 4-day criteria did not differ significantly from 315 patients whose manic episode lasted less than 4 days on a number of illness correlates on the Mood Swings Questionnaire (MSQ).
“Our study findings are strongly consistent with previous studies arguing that the clinical phenotype of [bipolar] II disorder (and its existence) is not dependent on a minimum duration of four days as imposed by DSM-IV and DSM-5, but further advanced by validation against a number of clinical correlates and not simply by examining phenomenological expression,” the researchers Gordon Parker (Prince of Wales Hospital, Sydney, Australia) and colleagues comment.
The only difference was that patients with brief manic episodes were more likely to rate manic symptoms as being less severe than those whose episodes lasted for 4 days. The average total MSQ scores were 49.6 and 57.0, respectively.
I personally have experienced a significant mood change for less than four days. It often occurred over a a period of three days and the mood switches within a day were almost like clock work. Given the arbitrariness of the rule I’m not surprised by this study’s finding.