Laboratory evaluation for Cushing's syndrome in psychiatric patients with cortisol nonsuppression following the overnight dexamethasone suppression test.

Laboratory tests used for the differential diagnosis of Cushing's syndrome have infrequently been employed in investigations of psychiatric patients who demonstrate hypothalamic-pituitary-adrenal (HPA) overactivity, and these laboratory procedures have not previously been applied for the specific purpose of further evaluating the endocrine function of psychiatric patients with serum cortisol nonsuppression following the standard 1-mg overnight Dexamethasone Suppression Test (DST). Low-dose (4 mg/48 hr) and high-dose (16 mg/48 hr) DSTs were administered to 10 psychiatric patients who exhibited cortisol nonsuppression after the overnight DST. Patients all had normal suppression to both the low-dose and high-dose tests. HPA overactivity in these patients was thus not sufficient to meet laboratory criteria for the diagnosis of Cushing's syndrome. Study results suggest that psychiatric patients with abnormal cortisol suppression following the 1-mg overnight DST are likely to have normal responses when assessed by standard laboratory protocols used for the diagnosis of Cushing's syndrome.