Postoperative follow-up of Cushing's disease using cortisol, desmopressin and coupled dexamethasone-desmopressin tests: a head-to-head comparison.

OBJECTIVE: Predicting the outcome of patients operated on for Cushing's disease (CD) is a challenging task. Our objective was to assess the accuracy of immediate postsurgical plasma cortisol, desmopressin test and the coupled dexamethasone-desmopressin test (CDDT) as predictors of outcome.

DESIGN AND PATIENTS: Sixty-seven patients with initial remission and a minimal postsurgical follow-up greater than 18 months were included in this retrospective bicentre study.

MEASUREMENTS: Follow-up included 3-6 months followed by yearly 24-h urinary-free cortisol, ACTH and cortisol plasmatic levels, a 1-mg overnight dexamethasone suppression test (1-mg DST), desmopressin test and the CDDT. ROC curves were performed to define the optimal threshold of immediate postsurgical cortisol level and 3- to 6-month desmopressin test and CDDT, as predictors of final outcome in comparison with classical biological markers of recurrence.

RESULTS: Eleven patients presented recurrence. The patient's median follow-up was 52 months (range, 18-180). As early predictors of outcome, immediate postsurgical plasma cortisol level <35 nmol/l predicted the lack of recurrence with 93% negative predictive value (NPV), whereas predictive positive value (PPV) was 25%. During the follow-up, the CDDT was more precise than the desmopressin test in predicting the lack of recurrence (100% NPV) when performed in the first 3 years after surgery. Positivity of the CDDT was defined based on ROC curves by ACTH and cortisol increments >50%. The CDDT was highly reproducible, as the same response was observed every year in 91% of the patients.

CONCLUSIONS: Adding the CDDT the first 3 years after surgery to immediate postsurgical cortisol evaluation should allow obtaining an optimal follow-up management of patients operated for Cushing's disease.