MON-082 - The Role of Endoscopic Ultrasound Guided Fine Needle Biopsy for Insulinoma Diagnosis in A Patient with Sudden Onset Hypoglycemia: A Rare Case of Insulinoma with Normal Insulin and Chromogranin Level

Introduction:
Insulinomas are rare functional pancreatic neuroendocrine tumors (pNETs) presenting with neuroglycopenic and adrenergic symptoms. Although rare, early diagnosis is critical to prevent morbidity from recurrent hypoglycemia. Endoscopic ultrasound (EUS) plays a crucial role in both localizing and diagnosing tissue. We present a case of insulinoma diagnosed via EUS-guided fine needle biopsy (FNA) after sudden-onset symptomatic hypoglycemia.

Case Summary:
A 54-year-old man with no significant past medical history presented with acute diaphoresis, confusion, and dizziness at work. Emergency department recorded a blood glucose of 26 mg/dL, which normalized after dextrose administration. In the ED, his labs showed glucose 64 mg/dL, insulin 16.9 μIU/mL, C-peptide 5.2 ng/mL, and chromogranin A 57.5 ng/mL. No exogenous insulin or sulfonylurea use was reported. These findings were inconclusive for endogenous hyperinsulinemia. Thus, a CT scan of the abdomen was obtained, which revealed a 2.9 cm enhancing mass in the pancreatic body. EUS showed a hyperechoic lesion in the same location. EUS-guided FNA was performed. Histology confirmed a well-differentiated neuroendocrine tumor positive for synaptophysin and chromogranin A, consistent with insulinoma. The patient was referred for elective surgical resection.

Discussion:
Although rare, insulinomas must be promptly diagnosed to prevent recurrent episodes of neuroglycopenia and associated morbidity. Most insulinomas are solitary, benign, and intrapancreatic, typically located in the head or body of the pancreas. Symptoms typically include both neuroglycopenic (confusion, dizziness, behavioral changes) and adrenergic (diaphoresis, palpitations) features. Diagnosis is classically guided by Whipple’s triad. Biochemical confirmation involves detecting inappropriately elevated insulin and C-peptide during hypoglycemia, ruling out exogenous insulin or secretagogues. In our case, although insulin and chromogranin A levels were within reference range, elevated C-peptide, radiologic imaging, and EUS-guided biopsy confirmed the diagnosis. EUS is highly sensitive (up to 94%) to detect pancreatic lesions, especially those < 2 cm, and allows simultaneous tissue acquisition. In this patient, EUS enabled both localization and histologic confirmation of the tumor—reinforcing the role of gastroenterologists in the multidisciplinary management of pancreatic NETs. Surgical resection remains the definitive and often curative treatment for benign insulinomas.

Conclusion:
This case underscores the critical role of the gastrointestinal specialist in diagnosing insulinoma through biochemical testing and EUS-guided biopsy. In patients with hypoglycemia of unclear etiology, early Gastroenterology consultation and EUS can expedite diagnosis, guide management, and potentially improve clinical outcomes.

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