A 38-year-old man has recurrent episodes of confusion relieved by eating. During a spontaneous attack, plasma glucose is 38 mg/dL with simultaneous insulin of 18 microU/mL and elevated C-peptide. Biochemistry confirms endogenous hyperinsulinaemia. The most appropriate next step to localise the lesion is:
- A Supervised 72-hour fast with periodic insulin, C-peptide, and sulphonylurea screen ✓
- B Selective arterial calcium stimulation with hepatic venous sampling
- C Distal pancreatectomy based on blind exploration findings
- D Octreotide scan followed by enucleation of any visible lesion
Correct answer: A. Supervised 72-hour fast with periodic insulin, C-peptide, and sulphonylurea screen
Explanation
The supervised 72-hour fast is the gold standard diagnostic test for insulinoma and is positive in over 95 percent of cases when blood glucose falls below 45 mg/dL with inappropriately high insulin, C-peptide, and proinsulin, plus a negative sulphonylurea screen. Localisation studies such as selective arterial stimulation, CT, endoscopic ultrasound, and intraoperative ultrasound come after biochemical confirmation. Blind distal pancreatectomy is obsolete because most insulinomas are solitary, benign, and less than 2 cm.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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