Insulinoma in Cats
Insulinomas are malignant neoplasms — fast growing cancerous tissue — of the beta cells in the pancreas. The beta cells primarily make and secrete insulin, which has a variety of effects in the body, the primary one being to regulate glucose throughout the body's cells. Because insulinomas secrete excessive insulin, the blood stream becomes low in glucose (hypoglycemia), which causes weakness and/or neurological problems. This disease does not effect cats as much as it does some other household pets, but it can and does occur.
The most common symptom of an insulinoma is physical collapse or loss of consciousness (syncope). Seizures, extreme weakness, and other neurological abnormalities are also common. Because the insulin is released periodically, symptoms are not consistent and frequency of symptoms is not necessarily predictable.
If your cat should collapse and a blood sample indicates low glucose, your veterinarian will suspect an insulinoma and will follow through with further tests to confirm it. Multiple blood samples may need to be taken over a period of time to determine a persistent low glucose concentration. Your veterinarian will also need to determine your cat's insulin concentration at the lowest glucose concentration.
It is common to fast from food before these tests are performed in order to determine true glucose levels. However, cats that do not eat are at high risk for a disease called hepatic lipidosis, so if your cat has not been eating due to loss of appetite, your veterinarian will advise you on the correct method for feeding (or not feeding) your cat before each test.
An amended insulin:glucose ratio (AIGR) may be useful when your cat's insulin level is in the lower end of the normal range. Insulinoma is still the expected finding in these types of cases. If the insulin level is inappropriately high for the decreased glucose level, an insulinoma may still be present.
Ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI) can be helpful in determining the extent of the pancreatic tumor and how much it is metastasizing. Typically, insulinomas will not metastasize to the lungs; however, chest X-rays may indicate other types of neoplasias as the cause for persistently decreased glucose. Scintigraphy, a form of imaging that uses radioactive isotopes to identify abnormal tissue, can also be used to identify the location of primary insulinomas and metastasis.