Partial sleep deprivation to prevent 48-hour mood cycles.

The course of a patient with the phenomenon of 48-h mood cycles, including her response to medication and to systematic partial sleep deprivation, is described. She had only a partial response to tranylcypromine alone. Partial sleep deprivation during the second half of alternate nights successfully prevented depressive mood cycles. Three to four weeks after discontinuing tranylcypromine she lost her ability to sustain this regimen. This case demonstrates an interaction between antidepressant medication and partial sleep deprivation in the prevention of depressive mood cycles.