Calcium Stimulation Test for Insulinoma Localization in an End-stage Renal Disease Patient on Diazoxide

Insulinomas are rare, and even rarer in patients with end-stage renal disease (ESRD). Clear criteria for the biochemical diagnosis of insulinomas in patients with renal failure have not been established, and hypoglycemia is often attributed to the renal disease itself, frequently leading to a delay in diagnosis. We describe a case of a patient who presented with asymptomatic recurrent hypoglycemia during hemodialysis. Disease progression and biochemical testing strongly suggested an insulinoma. Computed tomography (CT) of the abdomen and pelvis, In-pentetreotide scintigraphy and endoscopic ultrasound did not localize a pancreatic tumor. A calcium stimulation test was performed while the patient was taking diazoxide due to severe hypoglycemia with fasting for a couple of hours without treatment. The test showed a marked increase in insulin after calcium infusion in the dorsal pancreatic artery, localizing the tumor to the body and tail of the gland. Exploratory surgery easily identified a tumor at the body of the pancreas and pathology confirmed an insulin-secreting pancreatic neuroendocrine tumor. On follow-up, there was resolution of the hypoglycemia. We review the challenges of diagnosing an insulinoma in ESRD and describe a successful intra-arterial calcium stimulation test done in an ESRD patient while continuing diazoxide.