SAT598 7mg-dexamethasone Suppression Test For The Differential Diagnosis Of Cushing’s Syndrome

Abstract

Abstract Disclosure: D. Cuevas Ramos: None. G. Garza García: None. W. Hernández Núñez: None. F.J. Gómez Pérez: None. Introduction: Establishing the cause of Cushing’s syndrome remains challenging. Bilateral Inferior Petrosal Sinus Sampling (BIPSS) is the gold standard for distinguishing between Cushing's disease (ACHT-secreting pituitary adenoma) and an ectopic source of ACTH. However, BIPSS is an invasive test and is not widely available. Therefore, we sought to explore the diagnostic efficacy of the 7 mg dexamethasone suppression test (7mg-dexa) for establishing the diagnosis of Cushing's disease (CD). Methods: We reviewed 1375 cases with pituitary adenomas. From them, 191 cases had confirmed diagnosis of CD from 1999 to 2022. Of these, 25 patients underwent 7 mg dexamethasone suppression test together with BIPSS during their diagnosis workup. A diagnosis of CD was established in 21 patients, confirmed after neurosurgery, with a pathology report of ACTH+ secreting pituitary adenoma, and a biochemical resolution of CS. The additional 4 cases showed an adrenal source of CS. Suppression of 50% or more in the afternoon (of day 1 after 7 mg-dexa IV infusion by 7h starting at 7:00 hrs at 1 mg/hr) was considered consistent with CD. A central-to-peripheral plasma ACTH gradient of ≥2 before and after desmopressin stimulation was also considered consistent with CD during the BIPSS. We calculated kappa index to evaluate concordance between diagnostic test. Also, sensitivity (S), specificity (E), positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were calculated. Results: The mean age was 43±12.1 years, with a BMI of 30±5.6 kg/m2, 86% females. For the basal ACTH values during BIPSS, the S=76%, E=75%, PPV=94%, NPV=37%, LR+=3, LR-=0.3. For the post-stimulation BIPSS, the S=95%, E=75%, PPV=95%, NPV=75%, LR+=3, LR-=0.06. Using the 7mg-dexa, a S=91%, E=75%, PPV=95%, NPV=60%, LR+=3.6, LR-=0.12. Kappa between test was 0.6 before stimulation, and 0.7 after desmopressin stimulation showing acceptable concordance. Conclusion: The 7 mg-dexa showed similar and acceptable diagnostic performance in comparison with basal or stimulated BIPSS. Since 7mg-dexa inhibition test is less invasive and less expensive, further clinical research to evaluate its utility in CD diagnostic approach is in order. Presentation: Saturday, June 17, 2023