What is Insulinoma?
An insulinoma is a term for a tumor of the beta cells of the pancreas that secrete insulin. Insulin is responsible for removing glucose from the blood and putting it into storage in the body. Since glucose is the main fuel used by the brain and nervous system, low blood glucose levels lead to signs ranging from weakness to seizures and coma.
Affected dogs are usually middle aged to older. The clinical signs include weakness, lethargy, stumbling/tripping, collapse, seizures, or behavior changes. The body has significant protective mechanisms to protect itself against low blood glucose levels so the signs are typically intermittent, short lived and subtle initially. Exercise and excitement can worsen hypoglycemia which in the early stages can lead clinical signs to appear orthopedic in origin – short lived weakness after a walk or playtime may be interpreted as arthritis in older dogs.
On physical exam affected dogs usually appear normal. Complete lab work will reveal an abnormally low blood glucose level. Unlike other disease processes (liver disease, endocrine disease) that often have other lab work abnormalities, beta cell tumor patients are usually otherwise normal. To confirm an insulin producing tumor, the next step is to demonstrate an abnormally elevated insulin level when the blood glucose is low. In normal animals a low blood glucose occurs with a low insulin level. X-rays and an abdominal ultrasound are also indicated to further evaluate the abdomen for tumors.
Beta cell tumors are almost always malignant and have metastasized at diagnosis. The next step is diagnostics to evaluate the extent of metastasis if present. X-rays may identify a large mass if present. Abdominal ultrasound is usually the best noninvasive method for evaluation. Primary masses may be seen in the pancreas and metastasis may be noted in the lymph system or liver most commonly. The gold standard for diagnosis is surgical evaluation of the abdomen. This allows for visual inspection of the abdomen as well as palpation of the organs – in some cases the pancreatic tumors are too small to be seen but can be felt on palpation. Even this is not perfect as some microscopic metastasis may be present that can not be seen or felt.
Treatment is medical and in some cases surgical as well. Surgical removal of obvious tumors in the pancreas can lead to a cure or decrease in clinical signs. If metastasis is present when surgery is performed the clinical signs will eventually return. Complications of surgery include persistent clinical signs, diabetes and pancreatitis. Diabetes develops when the normal pancreatic tissue is not ready to make insulin on it’s own due to previous suppression by the tumor. Diabetes can be treated and typically resolves over time. Pancreatitis is inflammation of the pancreas that can be life threatening. Gentle handling of the pancreas during surgery helps decrease trauma and inflammation but can’t completely prevent it post operatively. Typically patients need to remain hospitalized for several days after surgery to help prevent and treat these complications. Medical treatment initially includes small frequent meals to keep blood glucose stable. Once this is no longer effective on its own steroids (most commonly prednisone) is started at a low dose and increased as clinical signs progress. The steroids help maintain blood glucose levels. Diazoxide is a drug that can be added if the steroids are no longer effective. Patients are typically euthanized when clinical signs persist and can no longer be managed