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Pancreatic Endocrine Tumors

Karen Eiler, DVM, MS, DACVIM (SAIM)

VCA West Los Angeles Animal Hospital, Los Angeles, CA, USA

Insulinoma Epidemiology

Etiology/Pathophysiology Insulinomas are uncommon in dogs and rare in cats.
One estimated report cites an incidence of 17.8/100 000
The pancreas is made up of endocrine and exocrine tis­ patient‐years in the dog and 12.6/100 000 patient‐years
sue. The endocrine pancreas is composed of islets of at risk in the cat. Insulinomas have been associated with
Langerhans, which make up approximately 1–2% of the multiple endocrine neoplasia (MEN) type I in people.
mass of the pancreas. Within the islets there are four cell This is an inherited disease that also results in parathy­
types: alpha, beta, delta, and polypeptide cells. Beta‐cells roid and pituitary tumors. Although we do not have a
secrete various hormones, with insulin being the pri­ clear understanding of the epidemiology of canine insu­
mary product. Approximately 60–75% of the islet cells linomas, there have been rare cases of canine MEN that
are of beta‐cell origin. involve an insulinoma.
Insulin is the hormone that is primarily responsible for
regulating blood glucose concentration. Insulin does not
influence entry of blood glucose into beta‐cells, as in Signalment
other tissues. Entry of glucose into the beta‐cell is pro­
portional to the blood glucose concentration. Beta‐cells In dogs, middle‐aged to older, medium to large breeds
are extremely sensitive to glucose concentrations and are predisposed. Large‐breed dogs are overrepresented.
therefore the regulation of insulin secretion. Breed predispositions have not been noted in cats.
The central nervous system (CNS) has limited glyco­
gen storage and is unable to use energy sources other
than glucose. Thus, it is dependent on blood glucose to History and Clinical Signs
maintain its energy requirements. With hypoglycemia, Clinical signs are predominantly related to hypoglyce­
cells within the cerebral cortex are affected first due to mia, resulting in neuroglycopenic manifestations and,
their higher metabolic rate. Counterregulatory hormones less commonly, stimulation of the sympathoadrenal sys­
such as catecholamine, glucagon, growth hormone, and tem. The degree and onset of clinical signs are related to
cortisol are secreted in response to hypoglycemia and aid the severity and rate of development of hypoglycemia.
in recovery from the hypoglycemic episode. Gradual or chronic hypoglycemia may go unnoticed.
Insulinomas (beta‐cell insulin‐secreting tumor, beta‐ When chronically affected by hypoglycemia, some ani­
cell adenocarcinoma/adenoma) are insulin‐secreting mals adjust to blood glucose levels of 20–30 mg/dL.
tumors of the pancreatic beta‐cells. They are the most Clinical symptoms consistent with hypoglycemia
common endocrine pancreatic tumor in companion ani­ include seizures, lethargy, weakness, coma, and ataxia.
mals and are usually malignant. Catecholamine release can cause tachycardia, muscle
Insulinomas can be found in both the right and left fasciculations, hunger, and restlessness. Exercise causes
lobes of the pancreas with equal frequency. Occult insu­ rapid consumption of glucose and may precipitate an
linomas are most frequently found in the pancreatic body. episode of collapse or seizure.

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical