Can an insulinoma cause hypoglycemia?

Can Insulinoma Cause Hypoglycemia?

Yes, insulinoma directly causes hypoglycemia through autonomous insulin secretion, and this is the defining pathophysiological feature of the tumor. 1, 2

Mechanism of Hypoglycemia

• Insulinomas are insulin-secreting pancreatic neuroendocrine tumors that produce excessive, unregulated insulin independent of blood glucose levels, resulting in hyperinsulinemic hypoglycemia 1, 2

• The hypoglycemia occurs because the tumor continuously secretes insulin even when blood glucose falls to dangerously low levels, overriding normal physiological feedback mechanisms 2

• More than 90% of insulinomas are benign tumors, but their insulin hypersecretion causes significant morbidity through recurrent hypoglycemic episodes 2

Clinical Presentation of Insulinoma-Induced Hypoglycemia

• Patients typically present with neuroglycopenic symptoms including confusion, lethargy, seizures, and in severe cases, unconsciousness 1, 3

• Symptoms characteristically occur during fasting states, particularly in the morning, when the autonomous insulin secretion is unopposed by dietary glucose intake 1

• Patients often experience weight gain due to frequent eating to prevent hypoglycemic episodes 1

• Autonomic symptoms from catecholamine release (sweating, palpitations, tremor) may also occur, though some patients present without these sympathetic symptoms, leading to diagnostic delays and misattribution to psychiatric or neurological disorders 3, 4

Diagnostic Confirmation

• The National Comprehensive Cancer Network recommends a supervised 48-72 hour fast as the first-line diagnostic test, continuing until hypoglycemia occurs or the time limit is reached 1

• At the termination of the fast, diagnostic criteria confirming insulinoma-induced hypoglycemia include:

  • Blood glucose <40-45 mg/dL 1
  • Insulin level >3 mcIU/mL (some sources suggest ≥6 IU/mL) 1, 2
  • C-peptide ≥0.6 ng/mL 1
  • Proinsulin levels ≥5 pmol/L 1

• Elevated C-peptide levels are critical for differentiating endogenous hyperinsulinemia from exogenous insulin administration 1

Critical Pitfall

• The diagnosis of insulinoma is frequently delayed because hypoglycemic symptoms are misattributed to psychiatric or neurological disorders, and this delay can lead to fatal outcomes from severe, untreated hypoglycemia 3, 4

• Clinicians must maintain high suspicion for insulinoma in any patient with recurrent episodes of confusion, altered consciousness, or seizures, particularly if symptoms occur during fasting or resolve with glucose administration 1, 3