II. Epidemiology
- Incidence: 1 to 32 cases per million person years
III. Pathophysiology
- Primary neuroendocrine tumor of the islet cell that secretes Insulin
- Associated with unregulated hyperinsulinemia due to excessive Insulin secretion from the islet cells
- Sporadic in most cases
- Associated with Multiple Endocrine Neoplasia Type 1 (MEN 1) in 6-7%
- Extrapancreatic tumors may also cause similar effects as a pareneoplastic syndrome
- Non-Islet cell tumors (NICTH) synthesize IGF-2 (or Insulin)
- Associated with Lung Cancer (including Mesothelioma), Sarcomas and gastrointestinal tumors
IV. Findings: Symptoms and Signs
- See Hypoglycemia
- Fasting Hypoglycemia
- Palpitations
- Neurologic changes
- Tremor
- Altered Level of Consciousness (Confusion to coma)
- Seizure
V. Diagnosis: Lab findings consistent with Insulinoma
- Serum Glucose <55 mg/dl
- Insulin >=3 uU/ml
- C-Peptide >= 0.6 ng/ml
- Proinsulin >=5 pmol/L
- Beta Hydroxybutyrate <=2.7 mmol/L
- Negative Sulfonylurea screen
VI. Differential Diagnosis
VII. Imaging
- Localize tumor
- CT Abdomen
- MRI Abdomen
- Endoscopic Ultrasound
- Also consider the less common extrapancreatic source if islet tumor not identified
- Non-Islet cell tumors or NICTH (Paraneoplastic Syndrome cases
VIII. Management
- See Hypoglycemia
- Surgical excision
- Most primary islet cell tumors are benign and surgery is curative
- Medical Therapy (If surgery delayed or ineffective)
- Diazoxide 300-1200 mg/day IV/PO PLUS a Diuretic
- Octreotide 150-150 ug/day divided doses SC
IX. Resources
- Insulinoma (StatPearls)