The Dexamethasone Suppression Test for Diagnosis and Prognosis in Psychiatry

A modified dexamethasone suppression test (DST) has had unprecedented evaluation among biologic tests proposed for clinical use in psychiatry. It has not proved to reflect pathophysiologic changes at the level of the central nervous system or pituitary, and tissue availability of dexamethasone itself may contribute to test outcome. The sensitivity of the DST in major depression is limited (about 44% in over 5,000 cases) but is higher in psychotic affective disorders and mixed manic-depressive states (67% to 78%). The high specificity of the DST vs control subjects (over 90%) is not maintained vs other psychiatric disorders (77% specificity overall), and acute "distress" may contribute to nonsuppression of cortisol. The test may have power in differentiating severe melancholic depression, mania, or acute psychosis from chronic psychosis (87% specificity) or dysthymia (77% specificity). The DST status adds about 11% to the prediction of short-term antidepressant response. Suggestions that failure to maintain normal suppression of cortisol predicts poor outcome are not secure. Uncritical enthusiasm or excessive skepticism regarding the DST are unwarranted.