Simultaneous and Bilateral Inferior Petrosal Sinus Sampling for the Diagnosis of Cushing’s Syndrome: Comparison of Multihormonal Assay, Baseline Multiple Sampling and ACTH-Releasing Hormone Test

Abstract

In 29 consecutive patients with adrenocorticotropin (ACTH)-dependent Cushing’s syndrome, we compared the usefulness of multiple baseline ACTH evaluations (10/29), multiple hormone evaluation (29/29) and ACTH-releasing hormone (CRH) stimulation (21/29) during simultaneous and bilateral inferior petrosal sinus sampling. The basal inferior petrosal sinus/periphery ratio for ACTH concentrations was greater than 2 in 18 of the 29 patients and CRH challenge caused the appearance of an inferior petrosal sinus/periphery ratio greater than 3 in 6 other patients. The presence of an ACTH-secreting adenoma was surgically proven in all the 24 patients who had an ACTH inferior petrosal sinus/periphery ratio greater than 2 basally or greater than 3 after the CRH test but also in 1 patient who had an inferior petrosal sinus/periphery ratio lower than 2 basally or 3 after the CRH test. In 4 patients, both the very high peripheral ACTH levels, the inferior petrosal sinus/periphery ratio and the complete lack of ACTH increase after CRH indicated the presence of an ectopic ACTH syndrome: a bronchial carcinoid was found in 2 patients, whereas the site of the tumor is still unknown in the remaining 2. An ACTH intersinus gradient greater than 1.4 was found in 23 patients. Among these 23 patients, the side of the adenoma was correctly predicted in 19 patients and wrongly in 4. In the 10 patients receiving ACTH level evaluation three times before performing the CRH test, no difference of ACTH concentrations was detected in 7 either in the periphery or in inferior petrosal sinuses, while in the remaining 3 patients the ACTH inferior petrosal sinus/periphery ratio became greater than 2 indicating Cushing’s disease. The presence of an intersinus gradient greater than 1.4 for β-endorphin was found basally in 19/29 patients (65.5%) whereas after CRH challenge in 21/29 patients. Moreover, in 4/21 patients (19%) it was clearer than the ACTH intersinus gradient in localizing the pituitary adenoma. Furthermore, in 13 patients a significant intersinus gradient, either basally or after CRH challenge, was found also for GH and/or PRL (44.8%) and in 5 patients for TSH, FSH and/or LH (17.3%). All the 4 patients with proven or suggested ectopic ACTH production had no intersinus gradient for whichever pituitary hormone was considered. In conclusion, the diagnostic accuracy of the inferior petrosal sinus sampling in our series was of 96.5% (28/29 cases) when considering basal and CRH-stimulated ACTH levels in the inferior petrosal sinuses and periphery. On the contrary, the multiple basal ACTH evaluation does not seem to be necessary when CRH is performed during the test, but may be helpful in a minority of cases when CRH test is not available. The multiple hormone evaluation, in particular β-endorphin level assay, might be performed in doubtful cases after the ACTH level determination is obtained, as it can help to indicate the presence of a pituitary microadenoma in the majority of patients.