Insulinoma
Insulinoma is an insulin-secreting pancreatic beta-cell tumor that causes fasting hypoglycemia through autonomous, glucose-independent insulin release. Diagnosis requires the Whipple triad plus biochemical confirmation of endogenous hyperinsulinism during a documented low glucose, most reliably with a supervised 72-hour fast. First-line treatment is surgical enucleation or resection, which is curative in the great majority of patients.
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What this article covers
- Overview
Insulinoma is a neuroendocrine tumor of pancreatic beta cells that secretes insulin without regard to the ambient glucose level, producing recurrent fasting hypoglycemia.
- Epidemiology
Most common pancreatic neuroendocrine tumor: Insulinoma is the most common pancreatic neuroendocrine tumor and the second most common neuroendocrine tumor of any organ.
- Risk factors
MEN1 germline mutation: A germline MEN1 mutation is the only established genetic risk factor, predisposing to insulinoma alongside parathyroid and pituitary tumors.
- Pathophysiology
Autonomous insulin secretion: Insulinoma arises from pancreatic beta cells that secrete insulin independent of the normal glucose-sensing feedback loop, so release continues even as glucose falls.
- Clinical features
Neuroglycopenic symptoms: Confusion, inappropriate affect, blurred or double vision, seizures, and loss of consciousness reflect the brain's dependence on a continuous glucose supply.
- Differential diagnosis
Exogenous insulin administration: Surreptitious or factitious insulin use raises serum insulin but suppresses endogenous secretion, so C-peptide and proinsulin are low rather than elevated.
- Diagnosis
What establishes the diagnosis: Insulinoma is confirmed when the Whipple triad is documented together with plasma glucose often below 50 mg/dL, insulin of at least 3 mcIU/mL, and C-peptide of at…
- Management
First, treat any acute hypoglycemia: Able to swallow: Oral carbohydrate.
- Complications
Neuroglycopenic injury: Prolonged or repeated severe hypoglycemia can cause seizures, coma, and permanent cognitive impairment if episodes go unrecognized.
- Prognosis
Benign, resected disease: Because insulinoma is usually small, solitary, and benign, complete surgical resection is curative in the great majority of patients, with low recurrence.
- Prevention
Early biochemical confirmation: Confirming the Whipple triad and endogenous hyperinsulinism before imaging prevents wasted workup and delayed diagnosis.
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Related articles
- Multiple endocrine neoplasia type 1
Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant tumor-suppressor syndrome causing parathyroid, pancreatic, and pituitary tumors, the '3 Ps.' First-line treatment is organ-specific: parathyroidectomy for hyperparathyroidism, dopamine agonists for prolactinoma, and surgical resection or acid suppression for pancreatic neuroendocrine tumors.
- Pancreatic neuroendocrine tumors (PanNETs)
Pancreatic neuroendocrine tumors (PanNETs) are islet-cell tumors that may be functional, producing a hormone-excess syndrome such as insulinoma or gastrinoma, or nonfunctioning and detected by mass effect or incidentally. First-line treatment is surgical resection when localized, with somatostatin analogues and acid suppression used to control hormone-excess symptoms before or in place of surgery.
- Hypoglycemia in adults
Hypoglycemia is a plasma glucose below 70 mg/dL, most often a complication of insulin or sulfonylurea therapy for diabetes, and in a person without diabetes it requires a Whipple triad-based evaluation for insulinoma or another endogenous cause. An alert patient is treated with 15 to 20 g of fast-acting oral carbohydrate, while a patient unable to swallow safely receives intramuscular glucagon 1 mg or intravenous dextrose 50% 25 g.
- Insulin autoimmune syndrome
Insulin autoimmune syndrome is spontaneous hyperinsulinemic hypoglycemia in a person without prior insulin exposure, caused by high-titer autoantibodies that bind endogenous insulin and release it unpredictably, or by antibodies that directly activate the insulin receptor. First-line treatment is dietary, with small frequent low-glycemic-index meals and avoidance of any culprit drug; refractory or severe recurrent hypoglycemia is treated with prednisone 30-60 mg orally once daily, tapered over 1 to 3 months.
- Sulfonylurea-induced hypoglycemia
Sulfonylurea or meglitinide exposure, whether a therapeutic misadventure, an accidental pediatric ingestion, an intentional overdose, or surreptitious administration, forces pancreatic insulin release independent of glucose and causes prolonged or recurrent hypoglycemia. A dextrose bolus alone provokes rebound hypoglycemia; the specific antidote is octreotide, given with a sustained dextrose infusion.
- Gastrinoma (Zollinger-Ellison syndrome)
Gastrinoma is a gastrin-secreting neuroendocrine tumor, usually arising in the duodenum or pancreas, that drives the acid hypersecretion of Zollinger-Ellison syndrome: recurrent, multiple, or refractory peptic ulcers plus diarrhea. Diagnosis rests on a markedly elevated fasting serum gastrin with a low gastric pH, then imaging to localize the tumor. First-line treatment is high-dose proton pump inhibitor therapy, with surgical resection when disease is not metastatic.
- Well-differentiated neuroendocrine tumors
Well-differentiated neuroendocrine tumors (formerly carcinoid tumors) arise from enterochromaffin and islet-type cells of the gut and pancreas, are graded G1 to G3 by Ki-67 and mitotic count, and may be functional (gastrinoma, insulinoma, glucagonoma, VIPoma, somatostatinoma, or carcinoid syndrome) or nonfunctional. Diagnosis rests on biopsy with neuroendocrine markers plus Ki-67 grading and somatostatin-receptor imaging, and management ranges from surgical resection to somatostatin analogues, peptide receptor radionuclide therapy, and targeted agents.