Objective: Identifying the cause of Cushing's syndrome (CS) is a perplexing issue. Bilateral inferior petrosal sinuses sampling (BIPSS) is an invasive and elaborate but established procedure in distinguishing Cushing's disease (CD) from ectopic adrenocorticotropic hormone (ACTH) syndrome. We compare the diagnostic performance of BIPSS and MRI in detecting an ACTH-secreting source, and we suggest the diagnostic protocol that we found beneficial for the management of patients with CS.
Materials and methods: Seventy-eight consecutive patients with CS were included. All patients underwent biochemical investigation and pituitary MRI. Consequently, patients were routinely referred for BIPSS; 25 received stimulation with corticotropin-releasing hormone (CRH) and 53 with CRH and desmopressin. The diagnosis of CD was established on the basis of complementary biochemical, imaging, and BIPSS criteria. The diagnostic performances of BIPSS and MRI were calculated for patients with final diagnosis.
Results: A final diagnosis was available for 54 patients (46 CD confirmed, five ectopic confirmed, three adrenals). No (known) patient was misclassified based on our suggested diagnostic criteria. MRI rendered 25 false-negatives and two false-positives (incidentalomas). Successful BIPSS yielded two false-negatives and three false-positives (adrenals). The calculated accuracy for detecting a pituitary source of ACTH was 50% and 88% for MRI and successful BIPSS, respectively.
Conclusion: MRI is of only limited diagnostic performance, while BIPSS is the most accurate way to establish the diagnosis of CD. The routine use of a multimodality diagnostic approach including BIPSS, MRI, and biochemical tests is suggested to avoid the risk of mismanagement for patients with CS.