An early post-operative ACTH suppression test can safely predict short- and long-term remission after surgery of Cushing's disease

PurposeThe present study evaluates the usefulness of an ACTH suppression test shortly after surgery, and to determine optimal cut-off values of included laboratory analyses, in predicting short- and long-term remission after surgery of Cushing's disease.MethodsA 48h suppression test with betamethasone 2mg/day applied after 45 transphenoidal adenomectomies in 28 patients was evaluated. Receiver operating characteristic (ROC)-curves were created for the included assays: plasma cortisol, plasma adrenocorticotropic hormone (ACTH) and urinary free cortisol (UFC). Plasma levels of cortisol and ACTH were measured both at 24 and 48h. Youden's index was used to determine cut-off with the highest sensitivity and specificity in predicting short- (3months) and long-term (5years or longer) remission. The area under curve (AUC) illustrated the clinical accuracy of the different assays.ResultsPlasma cortisol after 24h with betamethasone was most accurate in predicting both short- and long-term remission. 3months remission with cut-off 107nmol/L: sensitivity 0.85, specificity 0.94, positive predictive value (PPV) 0.96 and AUC 0.92 (95% CI 0.85-1). 5years remission with cut-off 49nmol/L: sensitivity: 0.94, specificity 0.93, PPV 0.88, AUC 0.98 (95% CI 0.95-1). Analyses of ACTH or UFC did not improve diagnostic accuracy.ConclusionsA 48h, 2mg/day betamethasone suppression test after transphenoidal surgery of Cushing's disease could predict short- and long-term remission with a high accuracy. Suppression of plasma cortisol after 24h with betamethasone to values excluding Cushings disease in the diagnostic setting yielded the highest accuracy in predicting long-term remission.