RESUMO
Different approaches are used to determine the cause of Cushing's syndrome (CS). In this study we evaluated the validity of nocturnal high dose dexamethasone and metyrapone tests in patients with CS of different etiology. A total of 61 patients (51 women, 10 men), aged 13-61, were studied. Definitive etiological diagnosis was established on imaging, surgical and pathological findings, and/ or the clinical evolution after treatment. On that basis, the patients were classified as follows: 41 with Cushing's disease, 16 with adrenal tumors (11 adenomas and 5 carcinomas) and 4 with ectopic CS. Nocturnal dexamethasone (8 mg) test was carried out in all the patients; in 43 out of the 61 patients, 11-deoxicortisol responses to metyrapone were also determined. The sensitivity, specificity, accuracy and positive predictive power for the diagnosis of pituitary CS were calculated for both tests. For the nocturnal dexamethasone test, values were 85, 100, 90 and 100%, respectively (n = 61); the sensitivity and specificity increased to 95 and 97% by repeating the test in six false negative patients. Results for the metyrapone test were 90, 85, 88 and 93%, respectively (n = 43). When both tests were considered together, the values were 97, 100, 98 and 100% higher, although not significantly, than those for each separate test (n = 43). In conclusion, we believe that the combination of metyrapone and nocturnal high dose dexamethasone tests carried out on an outpatient basis has enough sensitivity, specificity, diagnostic accuracy and positive predictive value to be employed as an easy and low cost strategy in the etiological diagnosis of CS.