Background: Bilateral inferior petrosal sinus sampling (BIPSS) is considered the gold standard for diagnosing ACTH-dependent Cushing’s syndrome caused by ACTH producing pituitary adenoma (APPA) or Cushing’s disease (CD). BIPSS has also been used to localize APPA. Pituitary MRI (PMRI) is also used to diagnose CD and localize APPA.

Objective: To investigate the accuracy of BIPSS vs. PMRI in the diagnosis of CD and localization of APPA.

Materials and Methods: This retrospective study in patients with proven CD was conducted at the Division of Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok during October 1999 to December 2015. The diagnosis of CD was proven by ACTH positive immunohistochemical study of the tumor and/or remission after pituitary surgery. The accuracy of BIPSS with and without desmopressin stimulation and PMRI in the diagnosis of CD and localization of APPA was assessed. The actual APPA location was confirmed by operative findings, type of operation and/or surgical outcomes.

Results: Thirty-two patients with CD were included. PMRI was performed prior to surgery in all patients and able to demonstrate APPA in 30 patients (93.8%). The accuracy of PMRI and HDDST in the diagnosis of CD was 93.8% and 83.9%, respectively. BIPSS was performed in 23 patients with 11 of them had desmopressin stimulation. The accuracy of BIPSS in the diagnosis of CD was 95.7% and 100% using diagnostic criteria of central to peripheral plasma ACTH ratio of ≥2 at baseline and ≥3 after desmopressin stimulation, respectively. BIPSS was able to diagnose CD in all patients with negative PMRI study. The accuracy of PMRI and BIPSS in predicting the site of APPA was 80.0% and 73.3%, respectively. The location or lateralization of APPA demonstrated by PMRI but not by BIPSS was significantly correlated with intraoperative findings (p <0.01). Factors associated with remission were correct lateralization of APPA by PMRI and postoperative basal serum cortisol level of <4 μg/dL.

Conclusion: BIPSS with or without desmopressin stimulation is more accurate than HDDST and PMRI for diagnosis of CD especially in patients with negative pituitary MRI study. However, PMRI is more accurate than BIPSS for localization of APPA. Correct localization of APPA diagnosed by PMRI is associated with a higher remission rate after surgery than that diagnosed by BIPSS.

Keywords: Thailand, bilateral inferior petrosal sinus sampling, pituitary magnetic resonance imaging, ACTH-producing pituitary adenoma, Cushing’ disease