An underlying circannual rhythm in seasonal affective disorder?

A patient diagnosed with seasonal affective disorder (SAD) carried out pros pective ratings of depression weekly for nearly a decade. A winter peak of depression and benzodiazepine intake was documented. However, over the year s, the depressive episodes shifted toward spring in an apparent free-runnin g circannual rhythm (periodogram peaks at 53 and 55 weeks). This patient ma y have an underlying seasonal propensity to depression no longer precisely entrained to environmental cues.