The Corticotropin-releasing hormone test in the postoperative evaluation of patients with cushing’s syndrome

After surgical cure of Cushing’s syndrome most patients develop transient secondary adrenal insufficiency that lasts for approximately 1 yr. Since ACTH-secreting pituitary adenomas generally respond to ovine CRH (oCRH), we tested the hypothesis that an early postoperative response to oCRH may indicate the presence of residual pituitary tumor and, therefore, predict recurrence. We also assessed the usefulness of oCRH for monitoring the recovery of the hypothalamic-pituitary-adrenal axis and for clarifying the pathophysiology of this condition. Thirty-four patients cured of Cushing’s syndrome (29 with Cushing’s disease, 3 with adrenal adenomas, and 2 with the ectopic ACTH syndrome) had an evening oCRH test 1-2 weeks after surgery. Nine patients (6 with Cushing’s disease, 2 with adrenal adenomas, and 1 with the ectopic ACTH syndrome) participated in a longitudinal evaluation and had repeated oCRH and 1-h ACTH tests at 2-month intervals for a year after surgery. Patients were considered to be cured on the basis of at least 3 subnormal urinary [<20 μg/24 h (<55 nmol/day)] or morning plasma cortisol levels [0600-0900 h; <6 μg/dL (<170 nmol/L)] in the first 2 weeks after surgery. The plasma ACTH and cortisol responses to oCRH in the early postoperative period were subnormal in 23 and normal in 6 patients with Cushing’s disease. Three patients developed recurrent Cushing’s disease (3, 3, and 23 months after transsphenoidal surgery). All 3 were among the 6 who had a normal early postoperative response to oCRH. All of the 23 patients who had a subnormal response to oCRH in the early postoperative period have remained in remission for an average followup period of 14 months (6-42 months). Thus, the recurrence rate was significantly greater in patients with normal oCRH tests in the early postoperative period (P < 0.001, by x² analysis). Surgically cured patients with adrenal adenomas or ectopic ACTH secretion also had subnormal plasma ACTH and cortisol responses to oCRH during the early postoperative period. During longitudinal evaluation for 12 months after surgery, the ACTH and cortisol responses to oCRH increased progressively (regardless of the cause of Cushing’s syndrome). Cortisol responses to oCRH correlated significantly with the cortisol responses to exogenous ACTH (r = 0.89; P < 0.00001). We conclude that most patients with Cushing’s syndrome have suppressed responses to oCRH during the early postoperative period. A normal early postoperative response in the patients with Cushing’s disease may identify a subgroup of patients who are at increased risk of recurrence.