Insulinoma

What is an Insulinoma?

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

Alternative Names: Insuloma; Islet cells adenoma

Causes, incidence, and risk factors:
The pancreas is an organ in the abdomen that makes the hormone insulin. Insulin is required to regulate blood sugar levels. Tumors of the pancreas that produce too much insulin (hyperinsulinemia) are called insulinomas.

High insulin levels cause low blood glucose (sugar), also called hypoglycemia. The hypoglycemia may be mild, leading to symptoms such as anxiety and hunger, or 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 hyperinsulinism have multiple pockets of overactive insulin-secreting cells in the pancreas, rather than a single discrete tumor.

Most insulinomas are not cancer. However, about five to ten percent are cancer. People with the genetic syndrome called multiple endocrine neoplasia Type I (MENI) are at risk for developing insulinomas.

Symptoms:

• sweating
• tremor
• rapid heart rate
• anxiety
• hunger
• dizziness
• headache
• clouding vision
• confusion
• behavioral changes
• convulsions
• loss of consciousness

Signs and tests:

• The person's blood may be tested while fasting (not eating). The person may have:
• low blood glucose
• high serum insulin level
• high C-peptide level

Other tests may include:

• CT scan or MRI of the abdomen to look for a pancreatic tumor
• Endoscopic ultrasound to look for a pancreatic tumor (when CT or MRI scan is normal)
• Octreotide scan to look for a pancreatic tumor (when CT or MRI scan is normal)
• Pancreatic arteriography (when CT or MRI scan is normal)
• Pancreatic venous sampling for insulin (when CT or MRI scan is normal)

Treatment:
Surgery is the preferred treatment for insulinoma. The location of the tumor is determined using diagnostic testing or surgical exploration. Single tumors are removed, but patients with multiple tumors usually require partial removal of the pancreas (partial pancreatectomy). At least 15% of the pancreas is left to prevent nutrient malabsorption from lack of pancreatic enzymes.

If no tumor is found during surgery or a patient is not a candidate for surgery, the drug diazoxide may be given to lower insulin secretion and avoid hypoglycemia. A diuretic (water pill) is given with this medication to keep the person's body from retaining fluid.

Octreotide has been used to suppress insulin secretion in some patients. Medication is also used to stabilize the person prior to surgery.

Support Groups:

Expectations (prognosis):
In a majority of cases, the tumor is benign and surgery is effective. However, a severe hypoglycemic reaction or the spread of cancerous tumors to other organs can be fatal.

Complications:

• severe hypoglycemic reaction
• cancerous tumor spreading (metastasis)

Calling your health care provider:
Call your health care provider if symptoms of insulinoma develop. Convulsions and decreased consciousness are emergency symptoms.