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

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.

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.

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.

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.