Endocrine Abstracts

Although bilateral inferior petrosal sinus sampling (BIPSS) is the most accurate procedure for the differential diagnosis of ACTH-dependent Cushing’s syndrome, a false-negative rate of 4–15% has been reported. An even lower sensitivity has been shown in patients with equivocal responses to CRH and/or high-dose dexamethasone suppression test (HDST). In the present study we investigated whether the administration of CRH plus desmopressin (DDAVP) during BIPPS, which is considered to be a more potent stimulus, improves the sensitivity without compromising the specificity of the procedure.

The results in 55 patients, 48 with confirmed Cushing’s disease (CD) (36 women, 12 men, mean age 42.4±12.5 years) and 7 with confirmed occult ectopic ACTH syndrome (oEAS) (1 woman, 6 men, mean age 44±20.4 years) that underwent BIPSS using a combined stimulus with CRH plus DDAVP were retrospectively analysed. The sensitivity for a basal IPS/P gradient >2 was 60.4%, with 100% specificity and a diagnostic accuracy of only 65.5%. After stimulation with DDAVP and CRH, 47/48 patients with CD had an IPS/P gradient> 2 but, none of the patients with oEAS, resulting in a sensitivity of 97.9%. The specificity was 100%, diagnostic accuracy 98.18% and the positive and the negative predictive values were 100% and 87.5%, respectively. A subgroup of 19 patients (17 with CD and 2 with oEAS) had contradictory responses to routine tests with CRH and/or HDST; sensitivity, specificity and accuracy of BIPSS in this subgroup were 100%.

In conclusion, the application of a combined stimulation with CRH plus DDAVP may be the preferred stimulus during BIPSS, since it seems to substantially decrease the false negative rate resulting in higher sensitivity but with no loss of specificity.