"Normal suppression" to dexamethasone in Cushing's disease: an expression of decreased metabolic clearance for dexamethasone.

The adrenal cortical function of a patient with pituitary-dependent Cushing's syndrome exhibited normal responsiveness to conventional doses of dexamethasone (Dex) over several years of evaluation. "Periodic hormonogenesis" did not seem to explain the phenomenon. Plasma concentrations of Dex were measured to ascertain whether an abnormality in Dex metabolism might explain the apparent discrepancy in Dex responsiveness. Plasma levels of Dex after oral administration of the steroid were higher than normal, suggesting that decreased clearance of Dex accounts for the phenomenon of "normal suppression" in this patient with Cushing's syndrome.