Circadian variation in the time of "switch" of a patient with 48-hour manic-depressive cycles.

A 43-year-old patient with regularly occurring 48-hr manic depressive cycles was studied intensively for about 2 years. While she was hospitalized, she was rated for manic behavior on a 15-point scale every 2 hr. Using predefined criteria, we have systematically analyzed 173 switches into mania and 171 switches out of mania with respect to their time of occurrence during the 24-hr day and the influence of time of switch on the intensity and duration of mania. A significantly higher number of switches into mania occurred at night (12 midnight to 8 AM) with peak incidence between 4 AM and 6 AM. Switches out of mania peaked between 10 PM and 12 midnight and also between 6 AM and 8 AM. Night switches into mania were also associated with a significantly higher peak mania rating than morning (8 AM to 4 PM) switches and higher rate of mania increment than morning and evening (4 PM to 12 midnight) switches. This indicates that time of day or circadian factors may determine the frequency and intensity of the manic process in this patient.