Endocrine Abstracts

JOINT4008

Background: Insulinoma is a rare neuroendocrine tumor with an incidence of one to four per million per year and its rarity can be partially attributed to diagnostic difficulties that even experienced physicians can face.

Case presentation: A 22-year-old nondiabetic male with a history of recurrent hypoglycemia with unknown etiology was brought to the hospital after being found down. At the scene, he was found to have a glucose level of 20 mg/dL by EMT and was given intravenous Dextrose 50% with improvement of mentation. He is nonalcoholic, has no known Liver or kidney disease, has no family history of diabetes, and is not on any medications. In the hospital, vital signs were normal. Physical examination was unremarkable. Laboratory tests were normal except for recurrent episodes of hypoglycemia confirmed with 72-hour fasting associated with diaphoresis and tremors relieved by glucose intake. Endocrinology was consulted and hypoglycemia testing showed elevated C-peptide 2.61 ng/mL (ref 0.5-2 ng/mL) and insulin level 31.2 uIU/mL (ref <15 uIU/mL), with normal Beta-hydroxybutyrate 0.08mmol/l (ref <0.49 mmol/l), Insulin antibody <0.4 nU/mL (ref <95 nU/mL), IGF-2 406 ng/mL (ref 265-616 ng/mL), IGF-1 209 ng/mL (ref 115-307 ng/mL), morning cortisol 18.5 mg/dL (ref 14-20 mg/dL), and negative Sulfonylurea test. Abdominal MRI and Endoscopic Ultrasound showed no pancreatic mass. A Selective Arterial Calcium Gluconate Stimulation Test (SACST) was done, which showed a fourfold increase in insulin level in the Gastroduodenal and Superior mesenteric arteries, indicating a tumor in the head or neck of the pancreas. He was started on diazoxide which improved his glucose, and he was discharged with outpatient planning for surgical exploration of the pancreas.

Discussion: Preoperative localization of insulinoma is vital since it dictates surgical success. However, current radiographic methods have low sensitivity which can have deleterious implications. SACST is 95-100% sensitive in diagnosing insulinoma as small as 2cm. Kam et al showed that out of forty-five biopsy-proven insulinomas, SACST definitively localized thirty-eight cases. This was concordant with Won et al where SACST definitively localized nine out of ten cases of insulinoma. It is also safe with no significant adverse events aside from mild nausea and skin flushing.

Conclusion: SACTS can be considered a safe and sensitive diagnostic procedure for localizing insulinomas when conventional imaging is nondiagnostic and can potentially improve clinical and surgical outcomes.

Reference: Guettier JM, Kam A. Localization of insulinomas by intraarterial calcium stimulation. J Clin Endocrinol Metab. 2009 Apr;94(4) PMID: 19190102; PMCID: PMC2682461.