Comparison of preoperative and postoperative ACTH concentrations after bilateral adrenalectomy in Cushing's disease

Up to one-third of subjects who have had bilateral adrenalectomy for treatment of Cushing's disease will develop Nelson's syndrome. To examine the value of pre-operative ACTH assays in predicting outcome, we have studied fifteen cases of Cushing's disease treated by bilateral adrenalectomy and pituitary irradiation. Three patients developed Nelson's syndrome. There was no significant correlation between preoperative ACTH level, either 8 am 'basal' or during metyrapone testing, and ACTH concentration post-treatment. Plasma ACTH concentration in the first year after treatment, however, showed a highly significant correlation with the latest postoperative value (n = 14, r = 0.684, P less than 0.01), even more marked when subjects with duration of follow-up less than 3 years were excluded (n = 11, r = 0.836, P less than 0.002). In nine of fifteen patients, plasma ACTH showed either no change or a definite fall during subsequent follow-up. We conclude that plasma ACTH measurement in the first post-operative year is a good indicator of eventual outcome. The continued fall in plasma ACTH shown in many patients after the first year of treatment suggests an effect of irradiation on the pituitary.