HIGH-DOSE DEXAMETHASONE SUPPRESSION TESTING VERSUS INFERIOR PETROSAL SINUS SAMPLING IN THE DIFFERENTIAL-DIAGNOSIS OF ADRENOCORTICOTROPIN-DEPENDENT CUSHINGS-SYNDROME - A DECISION-ANALYSIS

Differentiation of adrenocorticotropin (ACTH)-dependent Gushing's synd rome between Gushing's disease and the occult ectopic ACTH syndrome is difficult. Simultaneous bilateral inferior petrosal sinus sampling (I PSS) for ACTH levels in response to corticotropin-releasing hormone ha s high diagnostic accuracy, but its cost-effectiveness has not been an alyzed. In this study, decision analysis was used to compare two diagn ostic strategies: IPSS versus high-dose dexamethasone suppression (HDD ) followed by IPSS in those with a negative HDD test. Sensitivity anal yses were performed for all variables. The authors found that at 100% accuracy, IPSS has an incremental cost-effectiveness ratio of $1,000,0 00 per life saved. Incremental cost, incremental effectiveness, and in cremental cost-effectiveness are sensitive to the pretest probability of Gushing's disease, test characteristics, and test costs, As the pre test probability of Gushing's disease decreases, cost per life saved a lso decreases. As IPSS sensitivity and specificity rates decrease to l ess than 85%, the HDD strategy saves more lives and costs less. When t he HDD test has a 83% sensitivity rate and a 100% specificity rate, th e two strategies have equal effectiveness, and the HDD strategy remain s less expensive. The IPSS strategy saves lives whenever HDD specifici ty is less than 100%, When HDD is performed in the hospital at a cost of $2,000, the IPSS strategy is less expensive. The appropriate use of IPSS is dependent on the probability of Gushing's disease and the acc uracy and costs of the diagnostic tests. Even at relatively high opera tive risks and disutilities for transsphenoidal surgery, the cost for saving a life using the IPSS strategy is still high. The selective use of IPSS after a negative HDD is an attractive alternative, especially when the specificity of HDD approaches 100%.