Insulinoma

Signalment

• More common in dogs than cats
• Middle-aged to older dogs
• No sex predilection
• Breed predisposition, more common in medium to large-breed dogs:
  • Irish Setter
  • German Shepherd
  • Labrador Retriever
  • Standard Poodle
  • Boxer

Description

Insulinomas are well slow growing, encapsulated, functional tumours of the beta cells of the pancreatic islet cells, They secrete inaappropriately high amount of insulin irrespective of the serum glucose level. They are predominantly malignant (90% of canine isulinomas), with a high metastatic rate to regional lymph nodes, liver and omentum.

Diagnosis

Clinical Signs

The following signs are attributal to hypoglycaemia:

• collapse
• muscle tremor
• muscle weakness
• ataxia
• mentally dull and disorientated

These sigs may be intermittent at the beginning of the disease, but this becomes progressively more often. In between hypoglycaemic episodes, the animals are normal. A presumptive diagnosis can be made on the demonstration of the Wipple's triad. This includes presence of clinical signs associated with hypoglycaemia, fasting hypoglycaemia and amelioration of clinical signs with the admistration of glucose.

Laboratory Tests

Biochemistry

• Hypoglycemia

Other Tests

• Increased serum insulin level in the presence of hypoglycaemia confirms the diagnosis.

Diagnostic Imaging

Radiography

A thoracic radiograph may be used to identify any pulmonary metastases, but this is uncommon.

Ultrasonography

Occasionally, it may be possible to visualise the location of the tumour on the pancreas. However, this may not be possible if the tumous is too small. Metastases to lymph nodes and liver can sometimes be revealed.

Treatment

Medical

This is more suitable to patients which are not a good candidate for surgery such as signs of metastasis is present.

• Small and frequent meals (3-6 times/day), with a high protein and complex carbohydrate content, should be fed.
• Exercise restriction.
• Lowest possible dose of glucocorticoid given to increase hepatic glucose prodection and decrease cellular glucose uptake.

Surgery

A partial pancreatectomy is suitable for patients with a solitary tumour, provided there is no metastasis.

References

• Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company.
• Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.