SAT-873 - When Hyperinsulinemia Defies Conventional Imaging: A Case of Recurrent Severe Hypoglycemia

Background:

Endogenous hyperinsulinemic hypoglycemia is most commonly caused by insulinoma; however, diagnosis may be challenging when conventional imaging is unrevealing or when insulin antibodies are present, raising concern for autoimmune hypoglycemia.


Case:

We report an 80-year-old man with recurrent presyncope, diaphoresis, and episodic confusion occurring both fasting and postprandially, fulfilling Whipple's triad with a plasma glucose nadir of 25 mg/dL. Biochemical evaluation demonstrated marked hyperinsulinemia (insulin >1,000 µIU/mL), detectable C-peptide (1.9 ng/mL), suppressed beta-hydroxybutyrate, negative sulfonylurea screen, and positive insulin antibodies. Evaluation for adrenal, thyroid, and growth hormone deficiency was unremarkable. Initial localization studies including CT abdomen, MRI, abdominal ultrasound, and endoscopic ultrasound failed to identify a pancreatic lesion. Partial symptomatic improvement with prednisone and diazoxide raised suspicion for autoimmune insulin syndrome; however, hypoglycemia persisted with recurrent neuroglycopenic symptoms. Given ongoing severe hypoglycemia, Ga-68 DOTATATE PET/CT was pursued and demonstrated focal radiotracer uptake in the pancreatic tail suspicious for a neuroendocrine tumor. The patient subsequently underwent robotic-assisted distal pancreatectomy and splenectomy without complications. Pathologic examination revealed a 0.54-cm well-differentiated pancreatic neuroendocrine tumor consistent with insulinoma, Ki-67 < 3%, arising in a background of extensive pancreatic islet cell hyperplasia, with negative margins and no lymph node involvement (pT1N0). Postoperatively, hypoglycemia resolved clinically and on continuous glucose monitoring, allowing complete discontinuation of glucocorticoids and diazoxide.


Conclusion:

This case illustrates the diagnostic complexity of endogenous hyperinsulinemic hypoglycemia in the presence of insulin antibodies, highlights the utility of DOTATATE PET imaging in localizing occult insulinomas, and underscores that insulinoma should remain a key diagnostic consideration despite confounding autoimmune features.

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