The Addition of Corticotropin-Releasing Hormone to 2-day Low Dose Dexamethasone Suppression Test Provides Additional Case Detection

Abstract

Abstract PURPOSE: To assess the diagnostic value of adding a Corticotropin-Releasing Hormone (CRH) Stimulation Test to the 2-day Low Dose Dexamethasone Suppression Test (Dex-CRH Test). METHODS: We identified 65 patients with Cushing disease (CD) and 42 patients in whom a diagnosis of Cushing disease could not be confirmed (NCD) after a minimum follow-up of 14 months, all of whom had undergone the Dex-CRH test. RESULTS: The female sex ratio, median (range) age, and BMI were similar between the two groups. The follow-up for patients with CD and NCD was 66 (4-146) and 52 (14-146) months, respectively. Among 65 patients with CD, 5 (7.7%) had a cortisol level ≤ 1.4 µg/dl after LDDST but were appropriately classified as CD with a cortisol level >1.4 µg/dL at 15-min post CRH stimulation. In contrast, 3/42 patients (7.1%) in NCD had an abnormal Dex-CRH test. In only one of three patients, the LDDST was marginally normal (cortisol was 1.4 µg/dL and increased to 3.1 µg/dL 15-min post CRH). A cortisol cutoff value of > 1.4 µg/dL during the Dex-CRH test provided a sensitivity of 100%, specificity of 93%, and diagnostic accuracy of 97% to diagnose CD. Analysis that included only patients with a Dex level (n=74), the sensitivity did not change, but the specificity and accuracy of the Dex-CRH test increased to 97% and 99%, respectively. CONCLUSION: The Dex-CRH Test provided additional case detection in 5/65 (7.7%) patients with CD. It resulted in one false-positive case compared to LDDST. Measurement of dexamethasone improved the diagnostic accuracy of the test.