Relevance of inferior petrosal sinus sampling in the diagnosis of Cushing's syndrome: a case report.

Objectives: Non-specific signs and symptoms of Cushing's syndrome (CS) can pose a diagnostic challenge. Case presentation: We report the case of a man referred to the service of endocrinology for suspected CS. Hypercortisolism was confirmed on CS screening tests, whereas diagnostic tests confirmed the presence of adrenocorticotropin (ACTH) -dependent CS. The corticotropin-releasing hormone stimulation (CRH) test was performed to determine whether CS had an endogenous or ectopic origin. Since the CRH and the magnetic resonance imaging (MRI) test were negative, IPSS was performed and suggested that CS was originated in the pituitary glands. Transsphenoidal pituitary resection was carried out. Histopathological analysis confirmed the cortitotrope origin of the tumor. Conclusions: The etiological study and differential diagnosis of CS are complex processes that involve a variety of biochemical and imaging tests. It is important that a sequence of biochemical screening and diagnostic tests is performed, along with studies for establishing the location of the lesion, to determine whether CS has an adrenal, pituitary or ectopic origin. Despite its good diagnostic performance, the results of biochemical tests may not be conclusive, especially in ACTH-dependent CS. In the case reported, the inconclusive results obtained in the CRH test rendered an invasive procedure (IPSS) necessary, which ultimately confirmed diagnosis.