MON-311 - When Post-Bariatric Hypoglycemia Is Not Dumping Syndrome: A Case of Life-Threatening Insulinoma Presenting A Diagnostic Dilemma

Introduction: Insulinoma is a rare pancreatic neuroendocrine tumor with an incidence of 1–4 cases per million. In contrast, hypoglycemia after bariatric surgery is common, affecting 10%–75% of patients, while post-bariatric nesidioblastosis is rare but serious. We describe a patient with life-threatening hypoglycemia initially attributed to dumping syndrome whose persistent symptoms ultimately led to the diagnosis of insulinoma, underscoring the need for thorough evaluation in refractory hypoglycemia.

Case: A 46-year-old woman with obesity status post sleeve gastrectomy (~10 years prior), osteopenia, hypothyroidism, and systemic lupus erythematosus (on anifrolumab-fnia) presented with two weeks of persistent hypoglycemia. She reported longstanding post-bariatric hypoglycemia that had previously improved after starting anifrolumab-fnia. Despite D5 infusion, she experienced frequent blood glucose levels < 50 mg/dL and was admitted to the MICU. Dextrose was escalated to D10 and octreotide was initiated.

Given her bariatric history and an initially negative CT scan, post-bariatric nesidioblastosis was suspected. Octreotide was discontinued, and diazoxide was started with transient improvement. Acarbose and dietary modifications emphasizing complex carbohydrates, increased protein, and avoidance of simple sugars were added.

Laboratory evaluation showed elevated C-peptide (5.29 ng/mL) with normal high insulin at a glucose of 56 mg/dL. MRCP revealed a cystic lesion in the pancreatic tail, and endoscopic ultrasound demonstrated tail nodules. One lesion was biopsied and negative; the second was not biopsied due to high vascularity. Persistent hypoglycemia despite medical therapy prompted hepatobiliary surgery consultation. The patient underwent robotic distal pancreatectomy with en bloc splenectomy. Intraoperative frozen section identified multiple small lesions with clusters of neuroendocrine cells consistent with pancreatic microadenoma and neuroendocrine tumor. Final pathology was positive for insulinoma.

Postoperatively, she reported only one hypoglycemic episode. Continuous glucose monitoring showed minimal hypoglycemia (low 2%, very low < 1%), average glucose 130 mg/dL, GMI 6.4%, and low variability. She continues close endocrinology and surgical follow-up.

Discussion: This case highlights the importance of maintaining a broad differential diagnosis in patients with persistent hypoglycemia. A history of bariatric surgery may confound diagnosis and delay identification of rare but serious etiologies such as insulinoma. Multidisciplinary collaboration and persistence were essential in achieving an accurate diagnosis and definitive treatment.

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