Insulinoma

Alternative names
Insuloma; Islet cells adenoma

Definition
An insulinoma is a usually benigntumor of the insulin-secreting cells of the pancreas.

Causes, incidence, and risk factors

The pancreas is an organ in the abdomen that releases the hormone insulin. Insulin is required to regulate blood sugar levels. Tumors of the pancreas that produce excessive amounts of insulin (hyperinsulinemia) are called insulinomas.

High insulin levels cause hypoglycemia, or low blood glucose (sugar). Hypoglycemia caused by insulinomas may be mild and lead to symptoms such as anxiety and hunger, but patients are also at risk for severe hypoglycemia, which can cause seizures, coma, and even death.

Insulinomas are rare tumors that occur in about 1 out of 250,000 people. 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, rather than a discrete tumor.

Five to ten percent of insulinomas are malignant. Patients with the genetic syndrome called multiple endocrine neoplasia Type I (MENI), are at risk for insulinomas.

Symptoms

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

Signs and tests

     
  • during a monitored fast:       o low blood glucose       o high serum insulin level       o high C-peptide level  
  • CT scan or MRI of the abdomen to look for a pancreatic tumors  
  • Octreotide scan to look for pancreatic tumors (when CT or MRI scan is unrevealing)  
  • Pancreatic arteriography (when CT or MRI scan is unrevealing)  
  • Pancreatic venous sampling for insulin (when CT or MRI scan is unrevealing)

Treatment

Surgery is the preferred treatment for insulinoma. The tumor is localized with diagnostic testing or surgical exploration. Solitary 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 avoid malabsorption due to lack of pancreatic enzymes.

If no tumor is found at 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 is always given with this medication to avoid retaining too much salt. Octreotide has also been used to suppress insulin secretion in some patients. Medical treatment is also used to stabilize the person prior to surgery.

Expectations (prognosis)

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

Complications

     
  • severe hypoglycemic reaction  
  • tumormetastasis

Calling your health care provider

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

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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