Insulinoma With Ambiguous Biochemistry, Positive 68Ga-DOTA-Exendin-4 PET-CT, and Effective Endoscopic Ablation

A 75-year-old female presented with fasting hypoglycemic episodes. A supervised fast ended at 72 hours fulfilling Whipple triad, with suppressed insulin and C-peptide levels, but discordantly suppressed serum β-hydroxybutyrate levels. After 21 months of recurring symptoms, a repeat fast ended at 48 hours with Whipple triad, suppressed serum β-hydroxybutyrate level, and borderline nonsuppressed C-peptide level, suggesting endogenous hyperinsulinism. Serum insulin levels were discordantly suppressed. Computed tomography (CT) of the abdomen demonstrated an enhancing 1.36 × 0.93-cm nodule in the head of the pancreas. Endoscopic ultrasound (EUS)-guided fine-needle aspirate of the lesion derived cytology consistent with a neuroendocrine tumor, but fine-needle core biopsy returned normal pancreatic tissue. Because the results were equivocal, functional imaging with ⁶⁸Gallium-DOTA-exendin-4 positron emission tomography CT was performed, which confirmed the diagnosis of a single head-of-pancreas insulinoma. The patient declined surgical resection. Oral diazoxide therapy resulted in significant peripheral edema. Hence, EUS-guided radiofrequency ablation of the lesion was performed, and the patient remains symptom free 10 months postprocedure. This case illustrates that (1) exendin-4-based positron emission tomography may help one confidently diagnose and localize insulinoma when prior biochemical or endoscopic biopsy results are ambiguous; and (2) EUS-guided radiofrequency ablation is an efficacious alternative option to surgical resection in the frail, elderly patient with insulinoma.