Abstract
Objective: The primary aim of this study is to determine whether there is any difference in Dexamethasone Suppression Test (DST) between unipolar and bipolar cases with seasonal course.

Methods: Cases with seasonal affective disorder (SAD) (exhibiting seasonal course during SCID-I diagnostic interview, which is a longitudinal course determinant according to DSM-IV) that filled the informed consent form during their recovery period were taken into this study consecutively, during their clinic follow up. The average of age of 14 unipolar cases (13 female, 1 male) was 51.2±8.7; while the average of age of bipolar cases (6 female, 1 male) was 44.3±5.2 year.

Results: Inability to be suppressed with DBT was more frequent in bipolar cases with seasonal course (100%) than unipolar cases (42.8%). Although the ratio of female/male is similar between unipolar and bipolar SAD cases, bipolar cases are younger. In bipolar SAD, childhood trauma and premenstrual syndrome were reported more often, but previous stressor and social support before the first episode were less frequent. The first episode type in all of the bipolar cases was depressive period. In bipolar group, age of onset and age of starting prophylactic treatment were earlier, period until diagnosis was longer, episode severity was more, number of episodes was higher, but episode duration was shorter and functionality scores were higher. In bipolar cases total remission between episodes was 100%, treatment adherence was 92.9%. Bipolar disorder, childhood trauma, PMS, and severe episode were found as determinants of DST negativity in SAD based on regression analysis.

Conclusion: This study was the first one to compare unipolar and bipolar cases in seasonal affective disorder and found important differences. While HPA axis irregularity is expected in light reactive SAD cases, that have characteristic atypical vegetative symptoms during the depressive periods and severe depressive periods pose resistant challenge to treatment, in bipolar SAD cases it may be usual. Another important result of the study was that, seasonal affective disorder cases with insuppressible cortisol levels with DST showed better clinical course than the other group.

Key words: seasonal affective disorder, unipolar disorder, bipolar disorder, dexamethasone supression test