Quarterly Newsletter

2013-Oct-IVGNewsletter-InternalMedicine

The IVG Hospitals Quarterly Veterinary Newsletter features articles of interest to the veterinary medical community, written by veterinarians and veterinary specialists at our four locations.

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Insulinoma: How Not to Anger the Beast Tonya E. Boyle, DVM, DACVIM WE HAVE HAD THREE CASES OF INSULINOMA at Port City in the last few months so I thought this would be a good time to review this relatively uncommon condition in our canine and feline patients. Insulinoma is more common in dogs than cats, but it is important to remember that it does still occur in our feline patients. KEY POINTS OF THIS ARTICLE: Whenever a patient is presented with a blood glucose below 60, seizing or not, with or without possible reason, draw a blood sample for insulin:glucose ratio before administering dextrose. Once dextrose therapy is initiated, the opportunity to get this blood sample may not present itself again without consequences. If an insulinoma is suspected, give the smallest amount of dextrose to control the clinical signs do not let the glucose numbers influence your medical therapy of the patient. If clinically normal, a blood glucose of 47 may be very adequate for the patient. Prognosis is significantly improved with the addition of glucocorticoid therapy to medical management and may be implemented after surgical intervention or with dietary modification, if surgery is not an option. PATHOLOGY The etiology of insulinoma remains unknown. The effects of growth hormone locally (levels not measurable in serum) on insulinoma cells is suspected. Canine pancreatic islets of Langerhans are composed of 70% beta cells, perhaps explaining why insulin-secreting beta cell neoplasia is the most common pancreatic endocrine neoplasia in dogs. The majority of insulinomas are found histologically to be carcinoma, with adenoma being a rare histological Dr. Tonya Boyle practices at Port City Veterinary Referral Hospital in Portsmouth, NH. finding. Usually located in one of the limbs of the pancreas and not within the body, insulinomas are usually solitary tumors. The metastatic rate hovers around 50%, with regional lymph nodes and the liver being the most commonly affected organs, although any location is possible. PATHOPHYSIOLOGY Neoplastic proliferation of insulin-secreting beta cells causing excessive insulin release into the body, causing hypoglycemia. As in other causes of hypoglycemia (Somogyi phenomenon), counter-regulatory mechanisms are initiated to counter-act and protect the brain from a hypoglycemic state. Glucagon and catecholamines are the most effective mechanisms to elevate the blood sugar. Other counter-regulatory hormones that are activated include growth hormone and glucocorticoids. Insulin secretion is mostly regulated by glucose. In a normal patient, a blood glucose level less than 80 mg/dL will completely inhibit insulin secretion. With insulinoma, neoplastic beta cells will continue to secrete insulin independent of the blood glucose. Therefore, insulinoma may be diagnosed when the blood insulin level is documented to be high or normal, when the blood glucose is below 80 mg/dL. CLINICAL SIGNS Medium to large breed dogs are most commonly affected, but any breed may develop insulinoma. |6|

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