Insulinomas
are functional beta-cell tumors found in the pancreatic islet cells.
Beta-cells are responsible for the production of insulin under
normal conditions within the animal.
Glucose enters the beta cells independent of insulin and
stimulates the secretion of insulin when blood-glucose levels are
greater than 110 mg/dl and inhibits secretion when blood-glucose levels
are less than 60 mg/dl. Insulin
is the hormone responsible for lowering blood-glucose by “driving”
the glucose into tissue cells for utilization.
Dogs and cats are capable of euglycemia even when fasting,
therefore, blood-glucose level less than 60-70 mg/dl are considered
abnormal and there presence should warrant further diagnostics.
Most animals with insulinomas are middle age to older
with the median age being 10 years.
There are no gender or breed predilections in dogs and cats but
ferrets are usually male. The
duration of clinical signs is typically between 1-6 months with the most
common being seizure, weakness, collapse and or ataxia followed by
muscle twitching, lethargy and bizarre behavior.
Exercise, excitement, fasting and sometimes eating commonly evoke
signs. Physical exam
finding are usually unremarkable with the most common finding being
weight gain secondary to the anabolic effects of insulin. Insulinomas
are malignant tumors with most have metastases either microscopically or
grossly by the time clinical signs are present.
Frequent sights of metastases include intra-abdominal lymph
nodes, liver, mesentery, and omentum with rare metastases to the lungs.
Neoplastic beta cells are capable of excess hormonal
production of somatostatin, glucagons, serotonin, gastrin, pancreatic
peptide as well as insulin. Clinical
signs secondary to insulinomas are due to hyperinsulinemia leading to
hypoglycemia. The CNS needs
glucose to function properly; uptake of glucose by the CNS is insulin
independent hence hypoglycemia leads to neuroglucopenia causing
lethargy, weakness, ataxia, behavior change, seizures and coma. Hypoglycemia also stimulates the release of
counter-regulatory hormones (catecholamines and glucagon) causing
sympathoadrenal stimulation producing muscle tremors, nervousness,
restlessness and hunger.
Diagnostics and Sonographic Findings
Diagnostically, the only consistent finding on the
chemistry profile with insulinomas is hypoglycemia with the median blood
glucose = 39 mg/dl. In many
instances, blood-glucose levels may be within normal range.
If this is the case, check a fasting glucose, if the
blood-glucose drops below 60 mg/dl check the insulin levels from the
same blood sample, if they are normal or elevated an insulinoma is
present. Radiographs are
usually normal because the tumors are small, but they are important to
help rule out other causes of hypoglycemia such as acquired liver
disease, Addison’s disease, and non-beta cell tumors (hepatocellular
carcinoma, leiomyosarcoma). They
also help rule out metastatic disease to the lung or other organs before
surgery is preformed. Abdominal ultrasound may not reveal the insulinoma
because of its microscopic size but it is still extremely important
diagnostic test to perform and should be performed on all animals
suspicious of insulinoma prior to surgery. Ultrasound may reveal enlarged lymph nodes, nodules in the
liver or other organs. When
present, an ultrasound-guided fine needle aspirate or core biopsy should
be preformed to rule out reactive vs. regenerative vs. neoplasia.
Back to top
