Serial dexamethasone suppression tests in psychiatric illness: Part II. A study in major depressive disorder.

Weekly dexamethasone suppression tests (DSTs) were performed in 35 patients with major depressive disorder until clinical response. At initial evaluation, 65% of the patients showed nonsuppression, and 85.7% showed nonsuppression at least once during the treatment period. Normalization of the DST results usually coincided with or occurred before clinical recovery, although isolated "peaks" of DST nonsuppression occurred in 45.7% of the patients, irrespective of the clinical course. The test was not useful as a predictor of clinical recovery or relapse. Moderately ill depressed patients had significantly higher nonsuppression rates than schizophrenic or manic patients with corresponding severity scores, indicating that different factors might be associated with nonsuppression in different diagnoses. However, many abnormal DST results could neither be related to the course of the depression nor to the severity of illness; thus other factors must also be responsible for DST nonsuppression.