58-year-old man with early-morning confusion and glucose 42
A 58-year-old man with hypertension presents after two early-morning episodes of confusion, diaphoresis, and tremor that improved within minutes after drinking juice. He has no history of diabetes and takes no glucose-lowering medications. BMI is 31. During a supervised fast in the hospital, he develops neuroglycopenic symptoms when plasma glucose is 42 mg/dL; at that time insulin is elevated, C-peptide is elevated, proinsulin is elevated, beta-hydroxybutyrate is low, and the sulfonylurea screen is negative. Which of the following is the most likely next step in management?
See the answer and explanation below:
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A
Explanation
Clinical Pearl:
In an adult without diabetes, Whipple triad plus inappropriately elevated insulin, C-peptide, and proinsulin during fasting hypoglycemia with a negative sulfonylurea screen strongly supports endogenous hyperinsulinemia, most often insulinoma. Once biochemical confirmation is secured, the next step is localization for planned resection.
Explanation:
This patient has documented Whipple triad and biochemical evidence of endogenous hyperinsulinemic hypoglycemia during a supervised fast: insulin, C-peptide, and proinsulin remain inappropriately elevated when glucose is low, ketogenesis is suppressed, and the sulfonylurea screen is negative. That pattern is classic for insulinoma and current practice is to proceed with localization studies, followed by surgical resection when feasible. Glucocorticoids are appropriate for adrenal insufficiency, which causes low insulin states and would not explain this laboratory profile. Diazoxide can be used when surgery is not possible or while awaiting definitive treatment, but it is not the best next step after biochemical confirmation in an operable patient. Reactive hypoglycemia is usually postprandial, not reproduced on a supervised fast with this pattern of labs. Insulin autoantibodies are considered when exogenous insulin exposure is absent but insulin is high with a different clinical context, and they are not the primary next step when the fasting study already points to endogenous tumor-related insulin excess.
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