A longitudinal follow-up study of seasonal affective disorder.

OBJECTIVE: The purposes of this study were to evaluate the long-term stability of a seasonal pattern of recurrent depression, identify possible factors associated with alteration of the seasonal pattern, and determine whether atypical vegetative symptoms during early seasonal depressive episodes predict future seasonal relapses.
METHOD: The subjects were 41 patients satisfying the criteria used in the Japanese multicenter study of seasonal affective disorder who were consistently treated at the same outpatient clinic. Their longitudinal courses were evaluated by using case records and the Schedule for Affective Disorder and Schizophrenia--Life-time Version; the mean follow-up period was 10.4 years.
RESULTS: Nine subjects (22.0%) consistently showed a fall-winter pattern of recurrence throughout follow-up. Seventeen patients with an initial fall-winter pattern subsequently tended to shift seasons or show less seasonality. This alteration in pattern was possibly associated with antidepressant therapy or life events. Eleven patients with an initial diagnosis of nonseasonal affective disorder subsequently developed seasonal affective disorder; no specific factors were associated with this change. Atypical vegetative symptoms were significantly more common in patients with stable seasonal patterns of recurrence than in those who lost seasonality.
CONCLUSIONS: Although seasonal affective disorder appeared to be altered by antidepressant treatment, the presence of a core group of patients with a consistent seasonal pattern of recurrent depression suggests the validity of seasonal affective disorder as a distinct subtype of recurrent affective illness. The findings also suggest that atypical vegetative symptoms during early seasonal depressive episodes predict the subsequent seasonality of depression.