Insulinomas are tumors of the pancreatic beta-cells that secret excessive amounts of insulin, leading to clinical signs of hypoglycemia. They are rare neoplasms, occurring frequently in middle-aged to older dogs, with no apparent sex predilection, and almost always metastasize, even not showing malignant characteristics on histopathologic examination. A 10-year-old female Maltese dog was attended at Sena Madureira Veterinary Hospital in October 2008, with a history of seizures after bathing. During physical examination, the animal was alert, tachypneic, red mucous membranes, normal rectal temperature and blood glucose level was 25mg/dL. The animal was also obese. There was a previous episode of weakness one week before, when the dog was forced to a longer walk. Sodium, potassium, hepatic function and serum insulin dosage were measured (serum insulin was measured when blood glucose was 49 mg/dL). Abdominal ultrasound was performed, and no signs of pancreatic or abdominal nodules/masses were seen. After a period of one-day hospitalization, the dog was released with prescription of prednisone 0,25mg/kg PO once daily and a diet with complex carbohydrates, fibers and high fat, offered in many small meals during the day to help minimize a fast increase of blood glucose after feeding.

The owner was also oriented to avoid exercise and stressful events. One week after hospitalization, the owner said the dog was well, with no signs of weakness, tremors or collapse. Serum insulin was 460μU/mL. The amended insulin: glucose ratio (AIGR) was calculated: [serum insulin (micro U/mL) x100] ÷ [Blood glucose (mg/dL)-30]. AIGR > 30 suggests insulinoma; in this case was 2421,05). The owner refused exploratory laparotomy, and only medical therapy was instituted. The animal had a new crisis 40 days after, when owner discontinued medication, and was hospitalized in another clinic for treatment. No histological exam of pancreas was performed, so diagnosis was presumptive in this case. Rarely non-pancreatic tumors have been shown to produce insulin that can be assayed using conventional radioimmunoassay. This dog showed a good response with only medical management, even for a short time. Owner was refractory to surgery due to the age of the animal, and the high possibility of relapses soon after procedure. Long term prognosis is poor, even after surgical removal of neoplastic tissue, due to the high frequency of metastasis. But literature shows that medical management alone is associated with a shorter life expectancy, compared with animals that undergo surgery.