MON-035 Insulinoma in a Post Bariatric Surgery Patient: A Case Report

Abstract Disclosure: M. Ortega Abad: None. N.E. Fretes Oviedo: None. M. Eldib: None. G. Madrigal Loria: None. P. Rao: None. Introduction: Hypoglycemia can present with a variety of symptoms, some of which may be nonspecific. Conditions leading to hypoglycemia may arise due to endogenous hyperinsulinism, such as post-bariatric hypoglycemia, noninsulinoma pancreatogenous hypoglycemia syndrome, and insulinoma. It can also be associated with certain medications, critical illness or hormonal deficiencies. Case Presentation: A 69-year-old female with a history of sleeve gastrectomy in 1984 (resulting in 100 lb weight loss), peripartum cardiomyopathy, and meningioma presented to the endocrinology clinic for evaluation of hypoglycemia. Over the past two years, she had experienced intermittent episodes of brain fog, palpitations, shakiness, and presyncope both at rest and during exertion, some of which would awaken her from sleep. She was told in the past that her blood glucose was low, unclear levels, but did not have further work-up. She was undergoing cardiac and neurological evaluations for those symptoms. During an electroencephalogram (EEG), she became unresponsive, and a blood glucose level of 10 mg/dL was noted. She received treatment for hypoglycemia and was transferred to the emergency department. Further evaluation revealed a fasting blood glucose level of 52 mg/dL, β-hydroxybutyrate <0.1 mmol/L, insulin 108.6 mU/L, C-peptide 20.8 ng/mL, proinsulin 2600 pmol/L, and insulin autoantibody <0.4. A CT scan of the abdomen and pelvis revealed multiple pancreatic masses with coarse calcifications. The largest mass measured 6 cm in the body, with a smaller 3 cm mass in the tail. A biopsy of the pancreatic body mass confirmed insulinoma which was diagnosed 40 years after her bariatric surgery. An NM PET/CT scan showed SSTR2-expressing pancreatic lesions corresponding to the biopsy-proven insulinoma, with no evidence of distant metastasis. She is currently scheduled for a distal pancreatectomy. Discussion: The workup and diagnosis of hypoglycemia can often be challenging, particularly in post-bariatric patients who may develop hypoglycemia as a post-bariatric complication, which occurs in up to 80% of patients, typically within the first few years after surgery. The prevalence of insulinoma in these patients remains unknown. Conclusion: Insulinomas are rare neuroendocrine tumors, that greatly impair the quality of life and need to be expeditiously diagnosed and judiciously managed. The incidence of insulinoma in post-bariatric surgery patients is very rare, with most studies in the literature citing an incidence of < 1%, mainly from case reports. While it is easy to mistake post-bariatric surgery hypoglycemia as due to dumping/reactive hypoglycemia or increased insulin-sensitivity, this case highlights the need to be aware of insulinoma as a rare but potential cause in this patient cohort. Further investigation is warranted to understand its exact etiology and causative mechanisms. Presentation: Monday, July 14, 2025