To the Editor.—
Arató et al1 recently reported a "seasonal influence" on dexamethasone suppression test (DST) results in unipolar depression. They noted a "significantly less frequent DST nonsuppression in winter than in summer" based on a X2 statistic. In our opinion, the use of this statistic is in error. We agree that a general analysis of seasonal variation in DST makes sense, but there is no reason a priori to expect that any differences would be exclusively between summer and winter. Seasonal variations in affective disorders2,3 and associated biochemical measures occur during spring and fall.4,5 Beck-Friis et al6 noted a trend for a higher incidence of depression during spring and fall among patients with normal DST results, whereas patients with DST nonsuppression tended to be depressed equally throughout the year. Seasonal analyses of urinary corticosteroid and plasma cortisol levels have yielded patterns that span all
Brewerton TD, Gwirtsman HE. Seasonal Dexamethasone Suppression Test Results. Arch Gen Psychiatry. 1987;44(10):920. doi:10.1001/archpsyc.1987.01800220092014
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