Occult Insulinoma: A 19-Year Diagnostic Delay in a Patient With Recurrent Hypoglycemia

Recurrent hypoglycemia may present a diagnostic challenge when initial biochemical and imaging studies are inconclusive. We report the case of a 47-year-old man who presented with a 19-year history of recurrent hypoglycemic episodes characterized by diaphoresis, tremor, palpitations, intense hunger, dizziness, blurred vision, and impaired concentration. Initial evaluation documented hypoglycemia; however, insulin and C-peptide concentrations did not meet the diagnostic criteria for endogenous hyperinsulinism, and abdominal computed tomography (CT) failed to identify a pancreatic lesion. Persistent symptoms prompted reevaluation 19 years later, revealing endogenous hyperinsulinemic hypoglycemia and a 16-mm pancreatic body lesion on contrast-enhanced magnetic resonance imaging (MRI). The patient underwent distal pancreatectomy, and histopathological examination confirmed a well-differentiated pancreatic neuroendocrine tumor consistent with insulinoma. Following surgery, hypoglycemic symptoms completely resolved. This case highlights how insulinoma may remain clinically occult for prolonged periods when initial biochemical and imaging findings are nondiagnostic. Persistent or recurrent hypoglycemic symptoms should prompt continued clinical suspicion and periodic reassessment, even after inconclusive investigations, as repeat biochemical evaluation and evolving localization strategies may facilitate definitive diagnosis and treatment.