Phase-shifted diurnal rhythm of cortisol secretion in a patient with Cushing's syndrome due to adrenocortical adenoma.

A 21-year-old woman with Cushing's syndrome was found to have a marked diurnal variation in cortisol secretion. Serum cortisol concentrations and urinary excretion of 17-hydroxycorticosteroids were normal in the morning but clearly increased in the afternoon. The patient was cured by resection of an adrenocortical adenoma. ACTH and prostaglandin E1 stimulated cortisol release from incubated adenoma tissues in vitro. The cause of the abnormal diurnal rhythm of cortisol secretion is unknown.