Insulinomas are functional β-cell tumors of the pancreatic islet cells that are generally found in middle-aged to older dogs. No breed or gender predilection has been identified. Clinical signs may be present from 1 day to 3 years. Low glucose levels create a clinical picture that includes seizures, weakness, collapse or ataxia, and muscle twitching. Insulinomas respond to increased blood glucose levels-eating leads to an increase in blood glucose levels that may in turn lead to hypoglycemia 2 to 6 hours later due to a release of insulin from the tumor. The only consistent finding in dogs with insulinomas is low blood glucose levels. In a group of dogs with insulinomas, the median glucose level was 39 mg/dl. Occasionally, a random blood sample shows a normal glucose level. When the blood glucose level is less than 60 mg/dl, an insulin level from the same sample should be requested. Insulin levels greater than 10 µU/ml with glucose levels less than 60 mg/dl are diagnostic for insulinoma.

Survival times vary based on method of treatment and stage of tumor. Diet should be small, frequent meals high in fat, protein, and complex carbohydrates. Simple sugars should be avoided. Patients managed with surgery as well as medical therapy generally survive longer than those managed with medical therapy alone. Streptozotocin is being evaluated as a treatment. Although it is toxic to the kidneys, if streptozocin is given in conjunction with aggressive saline diuresis and pretreatment with butorphanol as an antiemetic, it may be helpful. However, it is unknown if this treatment adds survival time to the current life expectancy of 2 to 3 years of patients with treated insulinomas.

Insulinomas: a review and what's new. Garrett LD. ACVIM PROCEEDINGS, 2003, pp 444-446.