iSymptom

ConditionHormones & metabolism

Insulinoma

An insulinoma is a rare tumor of the pancreas that produces too much insulin, causing repeated episodes of low blood sugar (hypoglycemia), often when fasting, in the early morning or after exercise. Symptoms include sweating, shakiness, hunger, confusion, odd behavior, blurred vision and, if severe, seizures or loss of consciousness. About 9 in 10 insulinomas are benign and small. Surgical removal usually cures the condition completely.

Also called: Insulin-secreting tumor, pancreatic insulinoma, beta-cell tumor, pancreatic neuroendocrine tumor (functional)

By the iSymptom editorial team · Updated · 4 min read

At a glance

What it is
A pancreatic tumor of insulin-producing beta cells that releases insulin regardless of blood sugar.
Main symptom
Recurrent low blood sugar, especially when fasting or after exercise.
How common
Rare, a few cases per million people per year. The most common functioning pancreatic neuroendocrine tumor.
Diagnosis
Low blood sugar with inappropriately high insulin during a supervised fast, then imaging to find the tumor.
Treatment
Surgical removal, which cures most people.

When to get help

Call 911 or go to the ER

  • Unconsciousness, seizures or inability to swallow because of low blood sugar: call 911 or your local emergency number. If trained, give glucagon. Do not put food or drink in the mouth of someone who cannot swallow
  • Confusion or strange behavior that does not improve within 15 minutes of taking sugar

See a doctor within a day or two

  • Repeated episodes of shakiness, sweating, confusion or fainting relieved by eating, in someone without diabetes
  • Waking at night or in the morning confused, sweaty or with a headache
  • A blood sugar reading below 70 mg/dL (3.9 mmol/L) with symptoms in someone not taking diabetes medicines

Book a routine appointment

  • Unexplained weight gain from eating frequently to prevent symptoms
  • A family history of multiple endocrine neoplasia type 1 (MEN1) with any of these symptoms

Usually safe to manage at home

  • Mild symptoms of low blood sugar in someone who can swallow: take 15 grams of fast-acting sugar (such as 4 ounces of juice or glucose tablets), recheck in 15 minutes, then eat. Then contact a doctor, as recurrent episodes need investigation

How an insulinoma causes low blood sugar

Normally, beta cells in the pancreas release insulin when blood sugar rises and stop when it falls. An insulinoma releases insulin continuously, even when blood sugar is already low. Insulin drives sugar into cells and stops the liver from releasing stored glucose, so blood sugar drops, especially after several hours without food.

The brain depends on glucose, so low sugar affects thinking and behavior. Repeated episodes can blunt the body's warning symptoms over time, so some people become confused without first feeling shaky or sweaty.

Symptoms

Warning (autonomic) symptoms

  • Sweating
  • Shakiness or trembling
  • Fast heartbeat or palpitations
  • Hunger
  • Anxiety and irritability
  • Confusion, poor concentration and memory lapses
  • Odd or aggressive behavior, sometimes mistaken for drunkenness or a psychiatric problem
  • Blurred or double vision
  • Slurred speech and weakness
  • Seizures
  • Loss of consciousness

Symptoms typically occur in the early morning, after missing meals or after exercise, and improve after eating. Many people gain weight because they eat often to avoid symptoms.

Whipple's triad is a classic clue: symptoms of hypoglycemia, a documented low blood sugar at the time, and relief of symptoms when sugar is raised.

Causes and risk factors

Most insulinomas occur without a known cause. Around 5 to 10 percent occur as part of multiple endocrine neoplasia type 1 (MEN1), an inherited condition that also causes parathyroid and pituitary tumors. In MEN1, insulinomas are more often multiple. Insulinomas usually develop in people aged 40 to 60, but can occur at any age.

Diagnosis

Confirming excessive insulin

  • Supervised 72-hour fast: done in hospital. You fast while blood sugar is checked regularly. When hypoglycemia occurs, blood is taken to measure glucose, insulin, C-peptide (released with natural insulin), proinsulin and beta-hydroxybutyrate, and a screen for sulfonylurea medicines. Most insulinomas are diagnosed within the first 48 hours.
  • Key findings: low glucose with inappropriately high insulin, C-peptide and proinsulin, and no sulfonylureas in the blood.

These tests separate an insulinoma from insulin overdose or secret insulin use (where C-peptide is low), sulfonylurea use, and other causes of hypoglycemia.

Finding the tumor

Insulinomas are usually small, often under 2 cm, so finding them can be challenging:

  • CT or MRI of the pancreas
  • Endoscopic ultrasound (EUS): a probe passed into the stomach gives close-up images of the pancreas and can take a biopsy
  • GLP-1 receptor imaging (PET scans with exendin-based tracers) in specialized centers
  • Calcium stimulation test with hepatic venous sampling in difficult cases

Treatment

Surgery

Surgery is the main treatment and cures most benign insulinomas. Options include:

  • Enucleation: removing just the tumor, often by keyhole (laparoscopic) surgery.
  • Partial pancreatectomy: removing part of the pancreas, depending on the tumor's location.

Blood sugar usually returns to normal immediately after removal. Surgery is often done by a specialist pancreatic surgeon.

Other treatments

  • Frequent small meals and snacks, including at night, to prevent lows while awaiting surgery.
  • Diazoxide: a medicine that reduces insulin release.
  • Somatostatin analogs (octreotide or lanreotide) in some patients.
  • Endoscopic ultrasound-guided ablation for selected people who cannot have surgery.
  • Malignant insulinomas (about 1 in 10): surgery, everolimus, sunitinib, peptide receptor radionuclide therapy, liver-directed therapies and chemotherapy.

Outlook

After complete removal of a benign insulinoma, the cure rate is very high and life expectancy is normal. People with MEN1 need ongoing monitoring because new tumors can develop. Malignant insulinomas that have spread are less common and need long-term management, but many people live for years with treatment.

Frequently asked questions

What are the symptoms of an insulinoma?

Insulinomas cause repeated episodes of low blood sugar, with sweating, shakiness, hunger, palpitations, confusion, unusual behavior, blurred vision and sometimes seizures or loss of consciousness. Symptoms often occur when fasting, in the early morning or after exercise, and improve after eating.

How is an insulinoma diagnosed?

The key test is a supervised fast of up to 72 hours in hospital. If blood sugar falls while insulin, C-peptide and proinsulin remain high, an insulinoma is likely. Imaging such as CT, MRI and endoscopic ultrasound then locates the tumor.

Is an insulinoma cancerous?

About 9 in 10 insulinomas are benign and do not spread. About 1 in 10 are malignant, spreading to lymph nodes or the liver. Even benign insulinomas need treatment because recurrent low blood sugar can be dangerous.

Can an insulinoma be cured?

Yes. Surgical removal of a benign insulinoma cures most people, and blood sugar typically returns to normal right after surgery. People with MEN1 or malignant tumors need longer-term follow-up and sometimes additional treatment.

Sources

This guide was written from current patient and clinical guidance, including:

  • Endocrine Society: Evaluation and Management of Adult Hypoglycemic Disorders (Clinical Practice Guideline)
  • National Cancer Institute: Pancreatic Neuroendocrine Tumors (Islet Cell Tumors) Treatment (PDQ)
  • NANETS: Consensus guidelines for pancreatic neuroendocrine tumors
  • MedlinePlus: Insulinoma
  • NIDDK: Low blood glucose (hypoglycemia)