Endocrine Abstracts

Objective: To evaluate the results of the early postoperative low-dose (1 μg) ACTH (adrenocorticotropin) stimulation test in patients with Cushing’s disease (CD) in order to predict long-term outcome of transsphenoidal surgery.

Methods: We reviewed the serum cortisol response to 1 μg synthetic ACTH (1–24) in the second week after pituitary surgery in 40 patients with Cushing’s disease. Median follow-up was 48.5 months (range 6–106).

Results: Eighty-eight percent of patients in sustained remission (cure) recorded peak cortisol concentrations below 774 nmol/l (28.0 μg/dl) after stimulation with 1 μg synthetic ACTH. All patients with recurrent disease after initial remission (relapse) also showed ACTH-stimulated peak cortisol levels below 774 nmol/l. All patients with persistent Cushing’s disease after surgery (failures), except one, noted absolute peak cortisol levels greater than 774 nmol/l in response to ACTH stimulation.

Conclusion: The postoperative low-dose ACTH stimulation test can be useful in testing the integrity of the pituitary–adrenal axis after pituitary surgery. In patients with Cushing’s disease, the low-dose ACTH stimulation test has a sensitivity of 93% and a specificity of 88% in predicting immediate remission after pituitary surgery. Successful resection of a corticotroph adenoma causes a sudden drop in circulating plasma levels of endogenous ACTH. Subsequent down-regulation of ACTH-receptor expression in the adrenal cortex might explain the relative hyporesponsiveness to exogenous ACTH stimulation in patients in remission after pituitary surgery compared to patients with persistent Cushing’s disease.