Neuro-endocrine aspects of the dexamethasone suppression test in psychiatry

Abstract

A large proportion of patients with depression exhibit an increased activity of the hypothalamo-pituitary axis as assesed by measurement of excretion of urinary 17-hydroxy-corticosteroids (1), plasma cortisol levels (2) or urinary free cortisol excretion (3). The diurnal secretory pattern of plasma cortisol over a 24 h period shows an increased number and magnitude of secretory episodes in depressed patients (4). The adrenocortical response to exogeneous ACTH is normal (5), while an important test in the differential diagnosis of Cushing's syndrome is that the increase of plasma ACTH and cortisol concentrations in response to the stress of an insulin-induced hypoglycemia is in general normal in depressed and absent in patients with Cushing's syndrome (6). An interesting feature of the activation of the hypothalamo-pituitary-adrenal axis in at least 50% of depressed patients is an insufficient suppression of plasma cortisol concentrations in the overnight 1 or 2 mg dexamethasone test (7). It was shown in several studies (8, 9) that in the 2 mg dexamethasone suppression test (DST) non-suppressors had significantly higher urinary cortisol levels than suppressors, while all non-suppressors had urinary cortisol levels above the normal range. This correlation had not been observed in the 1 mg DST in several studies (9, 10, 11).