Dexamethasone suppression test in diagnosis of depressive illness

Neuroendocrine abnormalities present in depressive illness and use of the dexamethasone suppression test (DST) in diagnosing depression are reviewed. The coexistence of neuroendocrine disturbances and depressive illness may be explained by a central nervous system neurochemical abnormality. Norepinephrine appears to inhibit hypothalamic corticotropin-releasing factor, thus decreasing ACTH secretion by the pituitary and, in turn, cortisol secretion by the adrenal glands. Thus, a deficiency in brain norepinephrine may lead to both depressive symptoms and increased adrenal cortisol production. Episodes of cortisol secretion are longer and more frequent in depressed patients, and the circadian rhythm of cortisol release is altered. Dexamethasone does not suppress plasma cortisol levels in depressed patients as compared with normal subjects. Abnormal DST results were obtained in 40-70% of inpatients and 20-50% of outpatients diagnosed as having unipolar primary depression or major depressive illness. The incidence of abnormal DST results in most nondepressed psychiatric patients is comparable with that in normal subjects. DST results do not distinguish between unipolar and bipolar depression but may differentiate primary from secondary depression. Depressed patients with abnormal DSTs responded positively to drug treatment. DST nonsuppressors responded more favorably to norepinephrine-reuptake blockers, while DST suppressors preferentially improved with serotonin-reuptake blockers. Normalization of DST response has been associated with clinical improvement. Certain drugs, a number of psychiatric conditions, and several major physical illnesses may alter DST response. The DST is a commonly used and practical tool in evaluating depressive illness; however, its diagnostic value in depressed outpatients and elderly depressed patients is not clear.(ABSTRACT TRUNCATED AT 250 WORDS)