Bilateral inferior petrosal sinus sampling in the differential diagnosis of adrenocorticotropin-dependent Cushing's syndrome: A comparison with otherdiagnostic tests

To compare bilateral inferior petrosal sinus sampling (IPSS) with high dose dexamethasone (HDD) and CRH testing (using recently proposed stringent res ponse criteria) in the differential diagnosis of ACTH-dependent Gushing's s yndrome, we reviewed 53 consecutive cases. The main analysis was Limited to 45 cases with confirmed diagnosis: 44 with pituitary dependency, proven by confirmatory histology and/or significant biochemical improvement after pi tuitary surgery, and 1 with ectopic ACTH syndrome. After HDD (2 mg every 6 h for 48 h), 21 of the 44 pituitary cases met the stringent more than 90% s uppression criterion. Twenty-three of the 44 pituitary cases also underwent CRH testing; 16 of 23 met a stringent response criterion of a more than 50 % serum cortisol rise. For HDD and CRH testing combined, 8 of 23 fulfilled both stringent criteria, 10 of 23 had discordant results, and 5 of 23 faile d to fulfil either of the stringent criteria for pituitary dependency. IPSS was performed in all 44 of the proven pituitary cases; 36 had petrosal/per ipheral ACTH ratios of 2.0 or more without CRH stimulation. Thus, in patien ts with proven pituitary disease, stringent response criteria to HDD and CR H testing were fulfilled by only 48% and 70%, respectively. IPSS, which gav e direct evidence of pituitary ACTH secretion in 82% of the cases, is there fore considered necessary in a significant proportion of cases.