OVERNIGHT DEXAMETHASONE PRETREATMENT IMPROVES THE PERFORMANCE OF THE LYSINE-VASOPRESSIN TEST IN THE DIAGNOSIS OF CUSHINGS-SYNDROME

OBJECTIVE There is no endocrine test which is completely reliable for the confirmation of Cushing's syndrome and in separation of the variou s aetiologies. We have tested the hypothesis that overnight dexamethas one pre-treatment should result in a better performance of the lysine- vasopressin (LVP) test in the diagnosis of Cushing's syndrome. STUDY D ESIGN AND PATIENTS We studied 61 subjects, including 25 pituitary-depe ndent and 9 pituitary independent Cushing's (7 adrenal tumours and 2 e ctopic ACTH syndromes), 18 euadrenal controls, 4 depressed subjects, a nd 5 cushingoid patients. The subjects received 1 mg of dexamethasone orally at 2300 h and the following morning they were given 10 IU of ly sine-vasopressin im. MEASUREMENTS Plasma cortisol (RIA) was measured a t times -15, 0, 15, 30, 45, 60, 75, 90 and 120 minutes. RESULTS The de xamethasone-modified LVP (Dx/LVP) test resulted in four patterns of co rtisol response. The dexa sensitive pattern (positive suppression and negative response to LVP) was found in euadrenal subjects; the dexa in sensitive pattern (negative suppression and positive response to LVP) was seen in Cushing's disease; a nonresponsive pattern (negative suppr ession and negative response to LVP) was observed only in pituitary in dependent Cushing's; and an indeterminate pattern (positive suppressio n and positive response to LVP) was equivocal, being observed in 2 con trol subjects, 1 patient with Cushing's disease and 1 depressed patien t. In separating control subjects from Cushing's syndromes the Dx/LVP test had 88 . 9% sensitivity, 100% specificity and 96 . 2% diagnostic accuracy; when the test was used to segregate Cushing's disease from c ontrol subjects we found 96 . 0% sensitivity, 100% specificity and 97 . 7% diagnostic accuracy. The performance variables for the Dx/LVP tes t in separating pituitary dependent from pituitary independent Cushing 's were uniformly 100%. Depressed and cushingoid subjects did not diff er from control subjects in their cortisol patterns during the test, S uccessful removal of the pituitary microadenoma in Cushing's disease w as invariably followed by a reversal of the abnormal cortisol pattern (dexa insensitive) during the test to a dexa sensitive pattern indisti nguishable from that of control subjects. CONCLUSION These results con firm our hypothesis and suggest that an improved performance of any co rticotroph stimulus (oCRH, LVP, AVP or desmopressin) in the diagnosis of Cushing's syndrome should result from pre-treatment with dexamethas one.