RESUMEN
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 pituitarymicroadenomas (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 percent and the specificity 100 percent. 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 percent to 100 percent after Desmopressin stimulation. BIPSS accurately predicted the ¡ateralization of the microadenoma in 8 of 12 patients (66 percent). 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.