Insulinoma

An Insulinoma is a tumour of the pancreas which results in an excessive production of insulin. It can affect any dog, but large breeds are more prevalent and unfortunately these are invariably malignant tumours.

Clinical signs are sporadic and vague. They include reduced exercise tolerance, weakness, lethargy and collapsing episodes. This can progress to seizures. The over production of the hormone insulin by the tumour causes a low blood glucose then increased glucose utilisation at times of exercise, resulting in hypoglycaemia and therefore the clinical signs mentioned above.

An assumptive diagnosis is made by having repeated low blood glucose measurements in conjunction with increased insulin levels. An abdominal ultrasound or CT can confirm a mass within the pancreas. An important part of diagnosis is made by ruling out other causes of low blood glucose. A final diagnosis is made by surgical excision and histology of the tumour; however, it is advisable to check a chest X-ray first to ensure there is no secondary spread of the tumour to the lungs. Similarly, if there is evidence of spread to the liver or abdominal lymph nodes, surgical removal of the tumour is unlikely to be of benefit.

One of the major differential diagnoses is Addison’s disease. In the absence of any sign of secondary disease, surgical removal of the tumour results in the best chance of controlling clinical signs and improved survival times. Lymph nodes can be biopsied at the time of surgery to determine the extent of any secondary spread.

The removal of the tumour in the pancreas can cause a post-operative Pancreatitis. Many dogs develop diabetes post operatively and need to be treated with insulin injections whereas others may continue to suffer with hypoglycaemia. Survival time with surgery as long as the tumour hasn’t already spread can be up to 2 years.

Medical management is used to help control hypoglycaemia in those patients not undergoing surgery or continue to suffer with low blood glucose post operatively. Dietary management involves small frequent high fat and protein meals that aim to keep glucose levels constant and avoid triggering spikes in insulin. Oral steroids reduce the body’s sensitivity to insulin and increase glucose production in the liver. There are other drugs available- all aimed at managing hypoglycaemia.
In dogs with metastatic disease some forms of chemotherapy can extend survival times.