Inferior Petrosal Sinus Sampling in Adrenocorticotropic- Dependent Cushing’s Syndrome: Experience of a Tertiary Portuguese Hospital

Introduction: Adrenocorticotropic hormone (ACTH)-dependent Cushing syndrome is due to corticotroph adenoma or hyperplasia in 60 to 80% of the cases and in this setting it is called Cushing disease; less frequently, it results from an ectopic ACTH and/or corticotropin-releasing hormone (CRH) production. Distinguishing between these two conditions can be extremely difficult. Bilateral inferior petrosal sinus sampling is the gold-standard method for the differential diagnosis of ACTH-dependent Cushing syndrome. Methods: We retrospectively analyzed the fourteen bilateral inferior petrosal sinus sampling that were performed consecutively to fourteen patients with ACTH-dependent Cushing syndrome, between 2005 and 2016 in our hospital. ACTH levels from both inferior petrosal sinus and peripheral blood were measured before and after CRH administration – 0’, 5’, 10’ and 15’. Ratios of central-to-peripheral and interpetrosal ACTH levels were calculated. Results: Bilateral inferior petrosal sinus sampling was uneventfully performed in all patients. Results were suggestive of Cushing disease in twelve patients and of ectopic production of ACTH and/or CRH in two patients. Among patients with a central-to-peripheral ACTH gradient, this was observed in basal conditions in 10/12 (83.3%) and after CRH administration in the remaining. In the absence of a central-to-peripheral ACTH gradient, two patients were diagnosed as having ectopic ACTH and/ or CRH production. Tumor lateralization suggested by bilateral inferior petrosal sinus sampling was confirmed in 77.8% of the patients who underwent transsphenoidal surgery (n = 9) and the immunohistochemistry confirmed the ACTH-secreting pituitary adenoma in all of them. Three patients are waiting for surgery. Discussion: Inferior petrosal sinus sampling was a safe and well-tolerated procedure in our study group. It was effective in the differential diagnosis of ACTH-dependent Cushing syndrome and useful in planning Cushing disease surgical therapy.