Insulinoma
A rare pancreatic tumor that overproduces insulin
Quick Facts
- Type: Pancreatic neuroendocrine tumor
- Effect: Excess insulin, low blood sugar
- Most are: Small and noncancerous
- Main treatment: Surgery to remove the tumor
Overview
An insulinoma is a rare tumor that arises from the insulin-producing cells of the pancreas. Unlike normal cells, an insulinoma releases insulin in an uncontrolled way, regardless of the blood sugar level. Because insulin lowers blood sugar, this leads to repeated episodes of hypoglycemia (low blood sugar).
Most insulinomas are small and benign (noncancerous), and they are usually curable with surgery. The challenge is often recognizing the condition, because the symptoms of low blood sugar can be mistaken for other problems, including neurological or psychiatric conditions. Once diagnosed, treatment is usually very effective.
Symptoms
Symptoms come from low blood sugar and tend to occur when fasting, before meals, or after exercise. They fall into two groups:
- Effects on the brain (from sugar deprivation): Confusion, difficulty concentrating, blurred or double vision, dizziness, mood or behavior changes, and, in severe cases, seizures or loss of consciousness.
- Effects from the body's response to low sugar: Sweating, shakiness, palpitations, hunger, and anxiety.
Symptoms often improve quickly after eating or drinking something sugary. Severe low blood sugar with confusion, seizures, or unconsciousness is an emergency requiring immediate treatment.
Causes
An insulinoma is caused by an abnormal growth of insulin-producing cells in the pancreas that secrete insulin without regard to the body's needs. The reason these tumors form is usually unknown. Most occur on their own (sporadically).
In a minority of cases, insulinomas are part of an inherited condition called multiple endocrine neoplasia type 1 (MEN1), in which several hormone-producing glands tend to develop tumors. People with MEN1 may have more than one insulinoma.
Risk Factors
- Multiple endocrine neoplasia type 1 (MEN1), an inherited condition
- A family history of MEN1 or related hormone tumors
For most people with an insulinoma, no risk factor is identified, and the tumor occurs by chance.
Diagnosis
Diagnosis involves confirming low blood sugar caused by excess insulin and then locating the tumor:
- Supervised fasting test: Blood sugar, insulin, and related substances are measured during a closely monitored fast to show inappropriately high insulin when blood sugar is low.
- Blood tests to confirm the pattern of excess insulin and rule out other causes, such as diabetes medications.
- Imaging: CT, MRI, specialized ultrasound, or nuclear medicine scans to find the tumor, which can be small.
- Genetic evaluation if MEN1 is suspected.
Treatment
The main treatment is removing the tumor, which usually cures the condition.
- Surgery: Removing the insulinoma is the definitive treatment. Many are small and can be removed while preserving most of the pancreas.
- Medications: When surgery must be delayed or is not possible, certain medicines can reduce insulin release and help control low blood sugar.
- Dietary measures: Eating frequent meals and snacks can help prevent low blood sugar episodes before treatment.
- Treatment of rare cancerous insulinomas: A small minority are malignant and may need additional therapies.
After successful surgery, most people are free of symptoms and have a normal outlook.
Prevention
Insulinomas usually cannot be prevented because their cause is unknown. For people with the inherited condition MEN1, regular monitoring can help detect tumors early. In the meantime, those with symptoms can reduce low blood sugar episodes by:
- Eating regular meals and snacks, avoiding long gaps without food
- Carrying a fast-acting source of sugar
- Following any medical plan to manage blood sugar until treatment
When to See a Doctor
See a doctor if you have repeated episodes of confusion, sweating, shakiness, palpitations, or odd behavior that improve after eating, especially when fasting or before meals. Seek emergency care for:
- A seizure
- Loss of consciousness
- Severe confusion that does not improve quickly with sugar
Recurrent unexplained low blood sugar deserves medical evaluation, as it can have a treatable cause.
Frequently Asked Questions
What is an insulinoma?
An insulinoma is a rare tumor of the pancreas that produces too much insulin, causing repeated episodes of low blood sugar. Most are small and noncancerous, and they are usually cured by surgically removing the tumor.
What are the warning signs of an insulinoma?
Signs come from low blood sugar and include confusion, sweating, shakiness, palpitations, hunger, blurred vision, and mood changes, often when fasting or before meals and relieved by eating. Severe episodes can cause seizures or loss of consciousness.
How is an insulinoma diagnosed?
Doctors confirm that blood sugar drops while insulin is inappropriately high, usually with a closely supervised fasting test and blood work, then use imaging such as CT, MRI, or specialized ultrasound to locate the tumor.
Is an insulinoma cancer?
Most insulinomas are benign and not cancer. A small minority are malignant. Even so, the tumor causes problems by overproducing insulin, so it is usually removed regardless, and benign tumors are typically cured by surgery.
What should I do during a low blood sugar episode?
Eat or drink a fast-acting source of sugar, such as juice or glucose tablets, and recheck. For severe symptoms like confusion that does not resolve, a seizure, or loss of consciousness, call emergency services, as severe hypoglycemia is dangerous.
References
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
- National Organization for Rare Disorders (NORD). Insulinoma.
- MedlinePlus, U.S. National Library of Medicine. Insulinoma.
- National Cancer Institute (NCI). Pancreatic neuroendocrine tumors.