Insulinomas in cats

© Dr. Pamela Mouser, ADDL Graduate Student, http://www.addl.purdue.edu/newsletters/2006/Fall/FinalDX.htm

Insulinoma is a tumour derived from pancreatic beta-cells, which are the insulin-producing cells in the islets of Langerhans.  Insulinoma is rarely documented in cats, with only five reports identified in the literature, and is uncommon in dogs.  Interestingly, three of the five cats reported with insulinoma were Siamese.

In this type of tumour, neoplastic beta-cells produce insulin and can autonomously secrete the hormone, resulting in hyperinsulinemia.  Excess insulin causes hypoglycemia, which is the most consistent hematologic or serum biochemical abnormality in animals with insulinoma.  The classical manifestation, best characterized in the dog, is episodic neurological signs such as weakness, ataxia, syncope, or seizures during fasting or exercise when hypoglycemia becomes most severe.  After eliminating other causes of hypoglycemia, demonstration of inappropriate levels of insulin (i.e. normal or increased in the face of hypoglycemia) can help confirm the diagnosis of insulin-secreting neoplasia.  Ultrasound of the pancreas can assist in identification of the mass, although the tumors are commonly small (<3 cm) at the time of diagnosis, and can be difficult to detect.  Exploratory laparotomy may be warranted for definitive diagnosis.

Treatment for insulinoma can include surgery, medical management, or both.  Surgery is rarely curative, and can create new challenges by inciting pancreatitis, the most common post-operative complication.  Medical management consists of feeding frequent small meals, supplementing with glucocorticoids to counteract the hyperinsulinemia, and limiting excitement and exercise.  The goal is to keep glucose levels from falling dangerously low, rather than maintaining normal levels at all times.  Prognosis is poor due to challenging case management and high incidence of metastasis of this tumour.