Insulinoma

Definition

An insulinoma is a tumor in the pancreas that produces too much insulin.

Alternative Names

Insuloma; Islet cell adenoma

Causes, incidence, and risk factors

The pancreas is an organ in the abdomen that makes several enzymes and hormones, including the hormone insulin. Insulin's job is to reduce the level of sugar (glucose) in the blood by helping it move into cells.

Most of the time when your blood sugar level drops too low, the pancreas stops making insulin until your blood sugar returns to normal. Tumors of the pancreas that produce too much insulin are called insulinomas. Insulinomas keep making insulin, even when your blood sugar drops too low.

High blood insulin levels cause low blood sugar levels (hypoglycemia). Hypoglycemia may be mild, leading to symptoms such as anxiety and hunger. Or it can be severe, leading to seizures, coma, and even death.

Insulinomas are rare tumors. They usually occur as single, small tumors in adults.

These tumors are very rare in children. Most children with high blood insulin levels have many areas of overactive insulin-releasing cells in the pancreas, instead of a single tumor.

Taking medications that cause too much insulin in the blood, either accidentally or on purpose, is about as common as insulinoma.

More than 90% of insulinomas are non-cancerous (benign) tumors. People with the genetic syndrome called multiple endocrine neoplasia type I are at risk for insulinomas and other endocrine tumors.

Symptoms

• Anxiety
• Behavior changes
• Clouded vision
• Confusion
• Convulsions
• Dizziness
• Headache
• Hunger
• Loss of consciousness
• Rapid heart rate
• Sweating
• Tremor
• Weight gain

Signs and tests

After fasting, your blood may be tested for:

• Blood C-peptide level
• Blood glucose level
• Blood insulin level
• Drugs that cause the pancreas to release insulin

CT or MRI scan of the abdomen may be done to look for a tumor in the pancreas. If the test is negative, one of the following tests may be performed:

• Endoscopic ultrasound
• Octreotide scan
• Pancreatic arteriography
• Pancreatic venous sampling for insulin

Treatment

Surgery is the recommended treatment for insulinoma. The tumor is first found by tests or surgery. Medication may be used to get patients stable before surgery.

If there is a single tumor it will be removed. However, if there are many tumors, part of the pancreas will need to be removed (partial pancreatectomy). At least 15% of the pancreas must be left to produce its enzymes. This may prevent the surgeon from removing the whole insulinoma tumor.

If no tumor is found during surgery, or if you are not a candidate for surgery, you may get the drug diazoxide to lower insulin production and avoid hypoglycemia. A diuretic (water pill) is given with this medication to prevent the body from retaining fluid. Octreotide is used to reduce insulin release in some patients.

Support Groups

Expectations (prognosis)

In most cases, the tumor is non-cancerous (benign), and surgery can cure the disease. However, a severe hypoglycemic reaction or the spread of a cancerous tumor to other organs can be life-threatening.

Complications

• Severe hypoglycemic reaction
• Spreading of a cancerous tumor (metastasis)

Calling your health care provider

Call your health care provider if you develop any symptoms of insulinoma. Convulsions and decreased consciousness are an emergency -- call 911 or your local emergency number.

Prevention

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References

Cryer PE. Glucose homeostasis and hypoglycemia. In: Kronenberg HM, Shlomo M, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier;2008:chap 33.

Jensen RT, Norton JA. Endocrine tumors of the pancreas and gastrointestinal tract. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier;2010:chap 32.

National Cancer Institute. Islet cell tumors (pancreatic) treatment PDQ. Updated October 31, 2008.