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Canine Insulinoma: When the BG is “LO” and the dog doesn’t know! | VETgirl Veterinary Continuing Education Blog

In today's VETgirl online veterinary continuing education blog, Dr. Garret Pachtinger reviews hypoglycemia secondary to insulinoma in the dog. How do we diagnose and treat canine insulinomas in veterinary medicine?

Hypoglycemia, or a low blood glucose, is a common concern in veterinary medicine. Most often we deal with neonates or pediatric patients that come into the ER with neuroglycopenic signs of a low blood glucose including lethargy, weakness, ataxia, altered mentation, and seizures as a result of poor nutritional intake or gastrointestinal illness. But what happens when an adult dog comes into the ER, wagging their tail, happy as can be...but their blood glucose level is 35 mg/dL?

Of course...you first recheck the value to make sure the machine was working. Then you grab a 2nd glucometer to see if the first one is really working! Keep in mind that anemia or hemoconcentration can affect certain glucometers, so when in doubt, double check this blood sample on your chemistry analyzer.

After the 3rd reading, you begin to accept that the BG of 35 mg/dL may actually be real! The dog is not acting sick, is wagging their tail, and not not dehydrated at all! Although not an exhaustive list, your mind starts racing. What are the differentials for hypoglycemia in the adult dog?

Common differentials would include artifact (e.g., such as the analyzer machine not working correctly or a delay in separation of serum when you send the tube to an outside lab), liver disease (e.g., liver failure, vascular shunts), sepsis, hypoadrenocorticism, hunting dog hypoglycemia, xylitol toxicosis, or even beta-cell neoplasia (e.g., insulinoma).

So, keep in mind...Could this be the elusive insulinoma?

First, what is an insulinoma? An insulinoma is a functional tumor of the pancreas that produces excessive amounts of insulin without an appropriate trigger from the body to secrete insulin. The increased circulating insulin levels cause a significant drop in the blood glucose levels. As a result of this unregulated production of insulin, patients may present with signs of hypoglycemia including weakness, ataxia, lethargy, seizures, collapse and overall general weakness. In other cases, due to the chronicity of elevated insulin levels, the patient can even seem fairly normal despite such a low (chronic) blood glucose.

While the definitive diagnosis can only be made with a biopsy taken at the time of an exploratory surgery, here are a few diagnostics to consider in the diagnosis hunt:

1) Routine CBC and biochemistry panel: Not only will this confirm hypoglycemia but help rule-in or rule-out other differentials. For example, normal liver values, albumin, cholesterol, and BUN would help rule-out severe liver disease. Not only would sepsis be uncommon in a happy, wagging-tail dog, but also less likely based on a lack of a neutrophilia or left shift. Hypoadrenocorticism (classic) would also be unlikely if there is no lymphopenia or any notably electrolyte abnormalities (hyponatremia or hyperkalemia). NOTE: Please make sure to collect any blood samples prior to dextrose administration, and pull an extra red top serum tube for an insulin level while the blood glucose level in the patient is already low!

2) As hypoadrenocorticism is a differential for hypoglycemia, a baseline cortisol level should be considered. Based on the literature, hypoadrenocortisim is unlikely with a basal serum cortisol >2 μg/dL (>55 nmol/L).

3) Abdominal ultrasound: Although not perfect, an abdominal ultrasound can be helpful as a non-invasive and often less costly test than other advanced diagnostics to look for any abnormal abdominal lymph nodes, changes in the pancreas, or even evidence of metastasis to the liver. Don't forget to do chest radiographs (e.g., a three-view met check) first to rule out chest metastasis.

4) Understanding that normal pancreas beta cells secrete insulin when the blood glucose concentration is elevated, insulin in high concentration when the patient is hypoglycemic would be an inappropriate response of the body. For this reason, an insulin:glucose ratio can be a helpful diagnostic. A paired sample is submitted to the lab and interpreted together. If the insulin level is high despite a low glucose level, that is an inappropriate response and very concerning for an insulinoma. Again, please make sure to collect that extra red top serum tube for an insulin level while the blood glucose level in the patient is already low! You don't want to have to wait for your patient to become hypoglycemic again before pulling that blood sample!


5) While there are some advanced institutions that will consider additional diagnostics such as a CT scan or MRI to diagnose the insulinoma, many will take the above information, notably a happy wagging dog that is hypoglycemic with a high insulin:glucose ratio and recommend exploratory surgery.

Treatment:
Surgical management is the primary recommendation for canine insulinoma patients. The goal is to resect / remove the pancreatic insulin producing tumor. During surgery (and post-operatively), it is important to frequently monitoring blood glucose as surgical manipulation of the tumor may increase insulin production and therefore cause a worsening hypoglycemia.

If surgical management is not elected (e.g., financial, etc.) or recommended (e.g., metastasis, etc.), medical management is recommended for quality of life and reduction of clinical signs. Medical management options that have been investigated include:

  • Glucocorticoids
  • Diazoxide
  • Frequent small meals
  • Octreotide
  • Streptozotocin

Prognosis: If there is evidence of metastasis, the prognosis is unfortunately guarded. With that said, many dogs do well with surgical and/or medical management with postoperative survival times ranging from 1-3 years.

Dr. Garret Pachtinger, DACVECC
VETgirl Co-Founder and COO

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