Insulinoma

Insulinoma

By: Dr. Arnold Plotnick

Section: Information In-depth

The pancreas contains collections of cells called islets of Langerhans. Normal islets contain four cell types: alpha, beta, delta, and F cells. Each of these cell types produces a specific hormone. Beta cells produce insulin. Excessive amounts of insulin are released into the bloodstream when a malignant tumor (insulinoma) develops from the beta cells. In normal animals, insulin works with other hormones to maintain blood sugar concentration in the normal range (approximately 70 to 100 milligrams per deciliters of blood). Excessive secretion of insulin by the beta cell tumor (insulinoma) causes the blood sugar concentration to fall below the normal range (hypoglycemia) with several different possible symptoms including:

  • Seizures. Seizures are the most common symptom in dogs with insulinomas and occur in 68 percent of affected dogs.


  • Generalized weakness

  • Collapse or fainting (also called syncope)

  • Hind limb weakness

  • Lethargy

  • Incoordination

  • Muscle tremors

  • Excessive food consumption, also called polyphagia. Presumably dogs eat more in an attempt to maintain their blood sugar concentration in the normal range.

  • Exercise intolerance

  • Weight gain due to the growth-promoting (or anabolic) effects of insulin

    Most dogs with insulinomas display some of the symptoms listed above, but these symptoms tend to be intermittent and physical examination at the veterinarian's office usually is unremarkable. Other medical problems can lead to symptoms similar to those encountered in insulinoma. It is important to exclude these conditions before establishing a definitive diagnosis:

  • Some non-pancreatic tumors also can cause low blood sugar concentration, especially liver tumors, called hepatomas. There are several potential explanations why other tumors may cause low blood sugar concentration, including excessive glucose utilization by a very large tumor or secretion of a substance that mimics insulin in its effects.

  • Severe liver disease. The liver is a major storage site for glucose. Hypoglycemia may develop in advanced or severe liver disease when more than 70 percent of the liver is compromised.

  • Sepsis. Severe body-wide bacterial infection with widespread dissemination through the bloodstream may cause hypoglycemia, possibly due to increased utilization of the glucose by the bacteria.

  • Insulin overdose. Hypoglycemia may occur as a result of an accidental overdose of insulin in a diabetic animal.

  • Hypoadrenocorticism. Inadequate cortisol production by the adrenal glands, also called Addison's disease, may result from inadequate production and mobilization of glucose.

  • Hunting dog hypoglycemia. This poorly understood condition of nervous, thin hunting dogs may result in depletion of glucose stores in the liver and development of hypoglycemia.

     
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