Diagnosis and Treatment Course of Insulinoma Presenting as Hypoglycemia Unawareness Using a Factory-Calibrated Continuous Glucose Monitoring System

Objective: Rare disease Background: Insulinoma presenting only with postprandial hypoglycemia is difficult to diagnose. Repeated episodes of hypoglycemia can lead to "hypoglycemia unawareness", which can be even more dangerous and requires early detection and treatment. Case Report: We report the case of a 35-year-old man with an insulinoma presenting as postprandial hypoglycemia who was treated with diazoxide and monitored using a factory-calibrated continuous glucose monitoring (CGM) system until surgery. When the patient initially presented with hypoglycemia, relative hyperinsulinemia was present. There were no obvious abnormal findings on imaging examination. Hypoglycemia was not repeated on endocrinological examination, even while fasting. Four months later, asymptomatic postprandial hypoglycemia of 48 mg/dL was incidentally detected. Although none of the conventional 3 indicators of relative hyperinsulinemia were met, an insulinoma was suspected based on the results of a fasting test. Computed tomography and magnetic resonance imaging showed a mass in the pancreatic uncinate process, and selective intra-arterial calcium infusion revealed high insulin levels in the same area, leading to a diagnosis of insulinoma. The patient was treated medically with diazoxide, using a factory-calibrated CGM system until surgery. Subsequently, pancreatic mass enucleation was performed, and pathological examination confirmed the diagnosis. After surgery, the hypoglycemia resolved, and the blood glucose level remained within a range of 100 to 180 mg/dL, without the use of diazoxide. Conclusions: A factory-calibrated CGM system is useful for evaluating the course of medical treatment, monitoring hypoglycemic episodes during the diagnostic period, detecting unconscious hypoglycemia, monitoring the response to medical treatment, and treating insulinoma after surgery.