[Bilateral inferior petrosal sinus sampling in the differential diagnosis of ACTH-dependent Cushing's syndrome].

BACKGROUND

The features of pituitary ACTH-dependent Cushing syndrome are often indistinguishable from those of occult ectopic ACTH-dependent Cushing syndrome (CS).

AIM: To assess the diagnostic accuracy of bilateral inferior petrosal sinus sampling (BIPSS) in the differential diagnosis of ACTH-dependent Cushing's syndrome as compared with ACTH levels and the overnight high dose dexamethasone suppression test (HDDST).

MATERIAL AND

METHODS

Retrospective review of medical records of 23 patients (aged 19 to 63 years, 16 women) with surgically proven CS, 20 pituitary microadenomas (CD) and 3 with occult ectopic ACTH secretion (EAS).

RESULTS

No tumor was identifiable by imaging techniques. Mean plasma ACTH values were higher in patients with EAS than in CD (103+/- 110.2 and 73.1+/-41.98 pg/mL respectively, p=NS). Three patients with EAS and 3 patients with CD did not suppress cortisol with the HDDST. The sensitivity of the test was 86% and the specificity 100%. To improve the diagnostic outcome of BIPSS, an stimulation with Desmopressin (9 fig i.v) was performed in 9 patients. The threshold for a pituitary source, was defined as an inferior petrosal sinus to peripheral ACTH basal and post Desmopression ratio >2. BIPSS was successfully carried out in 22 patients and no complications occurred. In 6 patients BIPSS failed to meet the threshold criteria. In 3 patients, bronchial carcinoid tumors which proved to synthesize ACTH, were removed. The diagnostic sensitivity of BIPSS greatly improved from 86% to 100% after Desmopressin stimulation. BIPSS accurately predicted the inverted exclamation markateralization of the microadenoma in 8 of 12 patients (66%).

CONCLUSIONS

The combination of Desmopressin stimulation with BIPSS was useful for the differential diagnosis of ACTH-dependent Cushing's Syndrome. However, the preoperative location of pituitary microadenomas was poorly predicted by BIPSS.