SAT142 Utilization Of Continuous Glucose Monitoring In Diagnosis And Management Of Insulinoma
Authors: Phan Van , Kretschmer Philip , Pittas Anastassios G 
Published: October 2023

Abstract
Disclosure: V. Phan: None. P. kretschmer: None. A.G. Pittas: None.
Background: Insulinoma is a rare condition that can cause life-threatening hypoglycemia. Its diagnosis and management are challenging due to the requirement of a prolonged fasting test and frequent blood glucose testing. Continuous glucose monitoring (CGM) is widely available in diabetes management; however, its usage in people without diabetes is limited due to lack of evidence. Here, we report an acutely ill patient where we used professional CGM to streamline and expedite the diagnosis of insulinoma, and personal CGM to titrate medical management with diazoxide. Clinical Case: An 81-year-old woman with complex past medical history was admitted for chest pain and shortness of breath, found to have non-ST-elevation myocardial infarction. During inpatient work up, she experienced several hypoglycemia episodes that resolved with oral glucose intake. She had a history of recurrent hypoglycemia and prior MRI showing pancreatic tumor; however, outside records did not reveal biochemical work-up for insulinoma. Her symptoms were unpredictable, so a professional CGM (Freestyle Libre) was placed. CGM data revealed persistent nocturnal hypoglycemia, and occasional postprandial hypoglycemia. Patient-recorded symptoms were present in less than half of the hypoglycemic periods detected by CGM, indicating hypoglycemia unawareness. Given her acute cardiac condition and knowing her nocturnal hypoglycemia pattern from CGM, we performed a modified 72-hour fasting test that started at midnight and was able to capture a hypoglycemia episode within only 2.5 hours of initiation. Her plasma glucose was 57 mg/dL, insulin was 13 uIU/mL, C-peptide was 1.33 uIU/mL, and proinsulin was 9.5 pmol/L. She had a negative screen for sulfonylurea and there was no evidence of antibodies to insulin, suggesting a diagnosis of insulinoma. While awaiting localization studies, the patient was started on diazoxide. We used the personal CGM connected to our clinic portal to monitor glycemia at home and titrate diazoxide dose and frequency. CGM data showed nocturnal hypoglycemia and minimal daytime hypoglycemia, therefore, we recommended diazoxide only at bedtime to minimize daytime side effects and hyperglycemia. On one occasion, the patient was on as short course of prednisone which typically causes hyperglycemia during the day and hypoglycemia in early morning. CGM allowed us to monitor patterns of steroid-induced hyperglycemia, and we moved the prednisone dose to bedtime which resulted in euglycemia overnight. Conclusion: CGM can be a valuable tool in diagnosing and managing people with insulinomas. The CGM provides information about hypoglycemia frequency and pattern. It also helps detect hypoglycemia unawareness. With CGM, we can choose the right timing for 72-hour fasting test to minimize the length of the procedure. As outpatient, CGM also makes monitoring response to diazoxide a seamless process.
Presentation: Saturday, June 17, 2023