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. 60% of isulinomas are carcinomas, which are more likely to be endocrinologically active, the others being adenomas.

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. Insulinoma should be considered especially when clinical signs are associated with exercise, extended fasting or after feeding.

Laboratory Tests

Biochemistry

• Hypoglycemia

Other Tests

• A tentative diagnosis can be made if inappropriately high serum insulin level in the presence of hypoglycaemia is shown.

Histopathology

This is needed to confirm 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 in which surgery has been declined or when surgery is inappropriate or fails due to the presence of metastasis.

• Small and frequent meals (3-6 times/day) of a simple carbohydrate content.
• Exercise restriction.
• Prednisolone to increase hepatic glucose prodection and decrease cellular glucose uptake.
• Diazoxide, an oral hyperglycaemic drug, to inhibit pancreatic insulin secretion and tissue glucose uptake

Surgery

A partial pancreatectomy is suitable for patients with a solitary tumour, provided there is no metastasis. Complications such as persistent hypoglycaemia, pancreatitis, diabetes mellitus, epilepsy and diffuse polyneuropathy can occur.

Prognosis

Patients suitable for surgical excision has better prognosis than thoses treated medically.

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.
• Polton, G. A., White, R. N., Brearley, M. J. and Eastwood, J. M. (2007) Improved survival in a retrospective cohort of 28 dogs with insulinoma Journal of Small Animal Practice 48:151-156