Inappropriate secretion of adrenocorticotropin from corticotroph hyperplasia in a case of Addison's disease.

A patient with Addison's disease, treated with conventional hydrocortisone replacement, developed deep hyperpigmentation, headache and vomiting. Plasma adrenocorticotropin (ACTH) level was extremely high, showing abnormal diurnal rhythm. Suppression of ACTH with glucocorticoids was attenuated and the responses to ovine corticotropin-releasing hormone (oCRF) and lysine vasopressin (LVP) were absent. Magnetic resonance imaging (MRI) suggested an enlargement of the pituitary gland, while immunohistological examination of pituitary fragments obtained by transsphenoidal surgery revealed corticotroph hyperplasia without microadenoma. Postoperatively, plasma ACTH returned to normal and adequately responded to oCRF and LVP. Over the year since surgery, the symptoms have gradually improved and the patient has resumed normal activities.