Early postoperative LDDST enhances remission prediction beyond morning cortisol in cushing's disease.

PURPOSE: Transsphenoidal surgery (TSS) is the recommended treatment for Cushing's disease (CD). While low morning serum cortisol (MSeC) indicates early remission, the predictive value of an early postoperative overnight 2 mg low-dose dexamethasone suppression test (LDDST) remains unclear. This study compares the accuracy of early postoperative MSeC and LDDST for predicting early and long-term remission after TSS.

METHODS

We retrospectively analysed 342 CD surgical cases, who underwent TSS in our department between 2004 and 2024. Morning cortisol measurements were obtained postoperatively. An overnight 2 mg LDDST was performed on postoperative day five, in selected cases, preferentially in those without immediate postoperative biochemical remission (MSeC > 50 nmol/L), rather than as a universal screening test.

RESULTS

Immediate postoperative biochemical remission (IPBR; MSeC < 50 nmol/L) was achieved in 170 cases (49.7%). LDDST was performed in 197 cases (57.6%), with complete suppression (< 50 nmol/L) in 137 (69.5%). Remission at first follow-up (3-6 months) was significantly higher in cases with IPBR (99.4%) and/or complete LDDST suppression (98.5%) compared to those without (45.0%; p < .0001*). Long-term remission also correlated significantly with postoperative MSeC and LDDST (p < .0001*). ROC analyses confirmed strong predictive accuracy for remission during first FU (AUC MSeC: 0.9229; LDDST: 0.9413) and long-term (AUC MSeC: 0.8267; LDDST: 0.8058). Five-year recurrence risk was 71.1% without LDDST suppression versus 6.8% with suppression.

CONCLUSION

Early postoperative MSeC and LDDST are reliable predictors of remission after TSS in CD. MSeC < 50 nmol/L safely define biochemical remission. LDDST adds diagnostic value, particularly in cases with borderline, normal or elevated MSeC, and should be included in routine postoperative assessment.