The Dexamethasone-CRH Stimulation Test: A Single-Center Experience

Background: The diagnostic value of adding a Corticotropin Releasing Hormone (CRH) Stimulation Test to the 2-day Low Dose Dexamethasone Suppression Test (Dex-CRH Test) has been debated in the literature. We hypothesized that adding CRH to LDDST would provide additional case detection in patients suspected of having Cushing’s disease (CD). Methods: We identified 118 patients who underwent the Dex-CRH test to evaluate ACTH-dependent CS from a prospectively maintained pituitary database over 12 years. Seven patients were excluded (2 lost to follow up, 2 were on Dilantin with no available Dexamethasone (Dex) level, 2 had cyclic CD, and 1 suspected noncompliance with Dex intake). Three patients with ectopic ACTH Syndrome had very high cortisol levels after both LDDST and Dex-CRH tests. The remaining 108 patients are the subjects of this analysis. Patients were instructed to take 8 doses of Dex 0.5 mg PO every 6 hours starting at noon with the last dose of Dex taken at 6 AM. Ovine CRH injection (1 µg/kg, max 100 mcg) was given IV 2 hours afterwards. Cortisol was measured 2 hours after the last Dex dose prior to and 15 minutes after CRH administration. CD diagnosis was made based on positive ACTH staining on pituitary pathology and/or development of hypocortisolism postoperatively. Patients with no Cushing disease (NCD) are the group of patients in whom CD diagnosis could not be confirmed after a minimum follow up of 30 months. Results: Among 108 patients who underwent Dex-CRH test, 66 had CD and 42 had NCD. The female sex ratio, and median (range) for each of age, BMI, and follow-up duration in months were as follows with no statistically significant difference between the two groups: CD: 83%, 40 (15–82), 34 (30–42) and 63 (24–102). NCD: 88%, 40 (20–71), 37 (31–43) and 52 (30–67). Among 66 patients with CD, 5 patients (7.6%) 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 these three patients the LDDST was normal (cortisol post-Dex was 1.4 µg/dL and increased to 3.1 µg/dL 15-min post CRH). A cortisol cut-off value of > 1.4 µg/dL at 15 min during Dex-CRH test provided a sensitivity of 100%, specificity of 93%, and diagnostic accuracy of 97% to diagnose CD. When patients without a Dex level were excluded from the analysis (n=74), the sensitivity did not change but specificity and accuracy of Dex-CRH test further increased to 97% and 99%, respectively. Conclusion: The CRH test addition to the 2-day LDDST provided additional case detection in 5/66 (7.6%) of patients with CD. It resulted in one additional false-positive case compared to LDDST. Measurement of Dex level provided improved diagnostic accuracy of DEX-CRH test.