Desmopressin Stimulation Test Performance in ACTH-Dependent Cushing Syndrome

Background: Cushing syndrome (CS) is a set of diseases that develop when the body produces too much adrenocorticotropic hormone (ACTH). ACTH stimulates the production of a hormone called cortisol. Excess cortisol can cause serious issues, such as diabetes, high blood pressure, weight gain, and mood changes. Diagnosing CS early can be difficult. One test used to diagnose CS, the desmopressin (Desmo) stimulation test (DesmoST), has not been studied in enough people to know how accurate it is. Objective: To find ways to improve the DesmoST. Researchers especially want to learn more about how well the DesmoST identifies people with specific ACTH CSs: Cushing disease (CD) and ectopic ACTH syndrome (EAS). Eligibility: People aged 18 to 70 years who have or may have CS, especially CD or EAS. Healthy volunteers are also needed. Design: Participants with CS will have 3 DesmoSTs at least 48 hours apart. The procedure for each is as follows: They will limit their fluid intake the day before each test. They will have nothing to eat or drink for 12 hours before the test. For 1 of the tests, they will take a pill that contains a hormone (dexamethasone). They will take it around 11 pm the day before the test. Desmo is given through a tube attached to a needle inserted into a vein. Blood will be drawn a total of 6 times before and after the desmo is given. Healthy volunteers will have 4 DesmoSTs. These will be 2 to 14 days apart. All participants will have follow-up visits 3 to 5 days after each test. These visits may be by phone.