INSULINOMA

(original graphic by marvistavet.com)

WHAT THE PANCREAS NORMALLY DOES:

(original graphic by marvistavet.com)

The pancreas is a small light pink glandular organ nestled under the stomach and along side the duodenum (upper small intestine). The "endocrine" pancreas is the part of the pancreas that secretes hormones involved in blood sugar regulation, such as insulin and glucagon. The "exocrine" pancreas produces enzymes we use to digest our food. These two parts of the pancreas are not in separate areas but instead these two different types of pancreatic tissues are all mixed together throughout the entire pancreas.

The insulin-secreting cells are called “beta cells” and are bunched in groups called “Islets of Langerhans” which are scattered through out the pancreatic tissue. In some unfortunate individuals, the beta cells become tumorous and while the tumor itself can be very small, because it produces large amounts of insulin, its effects are very large. Insulin-secreting tumors are called, “insulinomas.”

The light pink tissue is an Islet of Langerhans (the insulin-secreting portion of the endocrine pancreas). The darker pink tissue is the digestive enzyme secreting exocrine pancreas. (Photocredit: Polarlys  via Wikimedia Commons)

WHAT HAPPENS TO THE PATIENT?

Insulin is a hormone secreted to store sugar. Normally it is secreted in response to the carbohydrates in a meal; it allows the extra sugar to be removed from the bloodstream and stored as starch and fat thus keeping the blood sugar level within the normal range. The function of normal islets of Langerhans is tightly regulated by the body but if there is an insulin-secreting tumor, the tumor is not subject to this regulation. Insulin secretion runs wild in this situation and low blood sugar (“hypoglycemia”) becomes a problem.

The hypoglycemia in this situation is typically severe most commonly resulting in seizures. Other clinical features include: listlessness, twitching, trembling, apparently drunken or wobbly gait, and reduced mental awareness.

• Toy Breed Puppy Hypoglycemia
• Diabetic patient possibly overdosing on insulin
• Pregnant female in labor having a difficult delivery
• Extreme exercise exertion as in “Hunting Dog Hypoglycemia”
• Starvation
• Over-whelming bacterial infection

Other not so obvious causes of hypoglycemia include liver disease, insulinoma, and hypoadrenocorticism (“Addison’s Disease”). The testing that is commonly needed beyond the basic panel would include: a resting cortisol level (a normal level largely rules out hypoadrenocortism), an ACTH Stimulation test (the definitive test for ruling out hypoadrenocorticism), an insulin level (which must be measured at the time the patient is hypoglycemic), and possibly a bile acids liver function test (if it is not clear if liver disease has been adequately ruled out by earlier findings).

What is Hypoadrenocorticism?

Hypoadrenocorticism is a deficiency in the production of cortisol (more commonly known as “cortisone”). Cortisol is produced by the adrenal gland and one of its functions is to raise blood sugar in anticipation of a fight or flight response. In more simple terms, if the body is anticipating exercise (such as fighting for one’s life or escaping a predator), blood sugar must be readily available for the muscles to burn. Cortisol is secreted to make that happen. (It also makes other metabolic adaptations happen as well but that is a story for another time.) Poor cortisol secretion can create episodes of hypoglycemia and since hypoadrenocorticism is easily treated once identified, it is very important to rule it out in a hypoglycemic patient.

For more information on this condition, click here.

The Insulin Level

To be meaningful in testing for insulinoma, the insulin level must be drawn when the patient’s blood sugar level is less than 60 mg/dl. This is because the insulin level is interpreted in light of the blood sugar level. In other words, an insulin level might be within the normal range for a normal patient but might be inappropriately high in a hypoglycemic patient.

STAGING INSULINOMA

Unfortunately, most insulinomas are malignant but that does not mean they are not treatable. There is more to prognosis and this is where staging comes in. Insulinomas can be confined to the pancreas (Stage I), spread to local lymph nodes (Stage II), or spread distantly, usually to the liver (Stage III). The therapy goal is to relieve the hypoglycemia and extend the period of normal life quality. Depending on the therapy selected, it is not unusual for the Stage I and Stage II dogs to live a year and a half or more while the Stage III dogs are looking at less than 6 months. Ultrasound is going to be very helpful in determining a patient's stage.

With ultrasound, lesions in the pancreas as small as 7mm in diameter can be identified and, in one study, ultrasound was able to locate the pancreatic tumor in 75% of cases. If ultrasound fails to locate the tumor, more advanced imaging such as CT (CAT) scanning is likely to find it. With the tumor being so small, knowing its location will be important in planning surgery.

TREATMENT: SURGERY

Surgical removal of the insulinoma is the treatment of choice. Even if cure cannot be achieved surgically, removing the majority of the insulin-secreting tissue should make a big difference in patient life-quality so ideally this is the best direction for therapy: locating the tumor (which, as mentioned can be very small) by imaging and removing it.

That said, surgical removal of the tumor is not a simple surgery. Manipulating the tumor can cause insulin surges which result in hypoglycemia during surgery; blood sugar levels must be tightly monitored both during and after surgery. Sugar-containing IV fluids are a must. Further, manipulation of the pancreas can create inflammation (“pancreatitis”) which is associated with pain and nausea.

Some patients have been exposed to excess insulin so long that their normal beta cells require a prolonged period to recover and during this time the patient may require insulin injections just as a diabetic patient would.

This all sounds like a lot of risk for the treatment of a tumor with a 90% chance of malignancy however, 50% of dogs without evidence of tumor spread at the time of surgery have had normal blood sugars for a year after partial removal of the pancreas. This is an excellent statistic and is often well worth the surgery. In one study, dogs receiving partial pancreas removal had a medial remission time of 496 days and the dogs that went on to receive medical management after signs recurred had a median survival of 1316 days. Dogs with medical management alone had a median survival of 196 days.

TREATMENT: MEDICATIONS THAT MANAGE HYPOGLYCEMIA

TREATMENT: MEDICATIONS TO COMBAT THE CANCER

Since insulinoma is a cancer, drugs of chemotherapy can be useful in suppressing tumor spread. Such medications are commonly used after surgery has removed the bulk of the tumor or when there is evidence that the tumor has spread. One would not consider such aggressive therapy, though, unless a biopsy has confirmed the tumor.

Streptozocin

This drug targets beta cells of the pancreas specifically. To avoid inducing kidney failure, it must be given with aggressive intravenous fluids thus hospitalization is required for its periodic use.

Other medications that have been used or are emerging include toceranib, doxorubicin, and alloxan. For the most up to date recommendations on chemotherapy it is necessary to see a veterinary oncologist.

TO LOCATE A VETERINARY ONCOLOGIST

http://vetcancersociety.org/pet-owners/find-a-vcs-member/

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Page posted: 11/19/10
Page last updated: 8/21/2021