Cushing's Syndrome Testing: Dexamethasone-CRH Test

Some individuals have high cortisol levels but do not develop the progressive effects of Cushing's syndrome, such as muscle weakness, fractures, and thinning of the skin. These individuals may have pseudo-Cushing's syndrome, which was originally described in people who were depressed or drank alcohol to excess, but is now known to be more common. Pseudo-Cushing's does not have the same long-term effects on health as Cushing's syndrome and does not require Cushing's syndrome treatment directed at the endocrine glands. Observation over months to years will distinguish pseudo-Cushing's from Cushing's syndrome. However, the dexamethasone-CRH test was developed to distinguish between the conditions more rapidly so that Cushing's syndrome patients can receive prompt treatment. This test combines the dexamethasone suppression and the CRH stimulation tests. Elevations of cortisol during this test suggest Cushing's syndrome.

 

Some patients may have sustained high cortisol levels without the effects of Cushing's syndrome. These high cortisol levels may be compensating for the body's resistance to the effects of cortisol. This rare syndrome of cortisol resistance is a genetic condition that causes hypertension and chronic androgen excess.

 

Sometimes, other conditions may be associated with symptoms of Cushing's syndrome. These include polycystic ovarian syndrome, which can cause menstrual disturbances, weight gain beginning in adolescence, excess hair growth, and impaired insulin action and diabetes. Commonly, weight gain, high blood pressure, and abnormal levels of cholesterol and triglycerides in the blood are associated with resistance to insulin action and diabetes; this has been described as "metabolic syndrome X." Patients with these disorders do not have abnormally elevated cortisol levels.