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 is needed to control blood sugar levels. Tumors of the pancreas that produce too much insulin are called insulinomas.

High 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.

They are very rare in children. Most children with hyperinsulinemia have many areas of overactive insulin-releasing cells in the pancreas, instead of a single tumor.

Accidentally or purposefully taking medications that cause too much insulin production is about as common as insulinoma.

Most insulinomas are non-cancerous (benign) tumors. Only 5 - 10% are cancerous. 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 glucose level
• Blood insulin level
• C-peptide 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 typical treatment for insulinoma. The location of the tumor is first found by tests or 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 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. Medication is also used to get patients stable before surgery.

Expectations (prognosis)

In most cases, the tumor is non-cancerous (benign), and surgery can treat 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.

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.