Thursday, May 15, 2014

Diet Recommendations for Dogs with Metastatic Insulinoma

My patient is “Ben,” a 10-year old, male Lab weighing 35 kg that presented with a 2-month history of having strange episodes, which included signs of disorientation and ataxia lasting from 10 minutes to 2 hours. The episodes were initially intermittent, but became much more frequent (2-3 times per day), so that the owner (finally) brought him in for an evaluation.

On physical exam, the dog was clinically normal. On our routine chemistry profile, the serum glucose value was very low (28 mg/dl; 1.56 mmol/l). We collected another blood sample for paired serum insulin and glucose concentrations. These test results showed an extremely low serum glucose concentration (25 ng/dl; 1.39 mmol/l) with a high serum insulin value (439 pmol/l; reference interval, 36-287 pmol/l).

An abdominal ultrasound showed a solitary 7-9 mm hypoechoic nodule on the pancreatic body between the pyloris and the proximal duodenal flexure. Unfortunately, multiple, small, very discrete solitary hypoechoic masses or nodules were also found throughout the liver, suggesting metastatic disease.

Based upon the hypoglycemia, hyperinsulinemia, and ultrasound findings, my presumptive diagnosis is insulinoma with metastasis to the liver. His owners have declined surgical exploration or biopsy.

We started Ben on oral prednisone (5 mg three times daily), and the owners have been feeding him small frequent meals. His improvement has been dramatic— no further episodes of disorientation or ataxia have been noted. I'm planning on keeping Ben on long-term, daily prednisone, but have some questions about the best diet to feed.

My understanding is that these dogs do best when fed frequent meals with high complex carbohydrates and low simple carbohydrates. I’ve also read that puppy diets are best, whereas others have said that a diabetic diet is better. But I was also concerned that a lower carbohydrate diet may not keep the blood glucose high enough. Which diets do you recommend?

My Response:

Unfortunately, there are no published studies to help us decide which is the best nutritional approach for management of dogs with insulinoma. This is not a very common endocrine tumor (1,2), so it’s difficult to do randomized trials that would evaluate the glucose response to different diets in dogs with insulinoma.

In my experience, there is not a single type of diet that will work well in all dogs. This is likely related to what stimulates that dog’s insulinoma to secrete insulin. In most dogs, hypoglycemia occurs most often during periods of fasting or exercise, whereas other dogs appear to develop the most severe signs of hypoglycemia after feeding (1,2).

Low carbohydrate, high protein diets?
Dogs with insulinomas should be fed every 4 to 8 hours, with a diet containing moderate to high levels of protein and fat and low amounts of simple carbohydrates (3). By avoiding simple sugars, an appropriate diet can dramatically reduce the stimulus for tumor insulin release, thereby controlling the clinical signs of hypoglycemia. The only exception is when a dog is actively exhibiting signs of hypoglycemia. In those cases, a rapidly absorbed source of sugar (such as honey, corn syrup, or maple syrup) may be administered orally at home pending further veterinary consultation (1,2).

Some dogs do well on a low-carbohydrate, high-protein diet, similar to what is commonly recommended for the diabetic cat. Most “young dog diets" fit reasonably well into this category. Since these diets are higher in fat, however, they can lead to weight gain in some dogs. Again, such low-carb diets reduce the stimulus for insulin secretion since these diets lessen postprandial hyperglycemia. During the metabolism of protein to glucose, glucose is liberated slowly into the blood stream, thus avoiding excessive production of insulin but providing a source of glucose over a prolonged period of time (4,5).

High-fiber, complex carbohydrate diet?
If a higher carbohydrate diet is fed, one containing complex carbohydrate and/or high fiber is ideal, since the digestion and absorption of carbohydrates should be slower and the rise in blood glucose more sustained over time (2). However, as opposed to the lower carbohydrate, higher fat diets, these high fiber diets tend to be low in energy density; therefore, if the dog is underweight or starts to lose weight, this type of diet might not be the best choice.

Bottom line
A number of different types of diets can be used to help manage the signs of hypoglycemia in dogs with insulinoma. Some dogs will do best on low carb diets, whereas others may respond better to a higher fiber diet. Whatever type of diet is chosen, multiple small feedings a day are indicated.

But remember: diet therapy generally plays only a minor role in management of dogs with insulinoma. Surgical resection of gross pancreatic disease is the treatment of choice and should always be considered, even in dogs with known metastatic disease. If surgery is not possible or it fails to control hypoglycemia, glucocorticoids (prednisone) and diazoxide are two drugs commonly used in conjunction with diet for the long-term management of dogs with insulinoma (1,2,6,7).

Overall, the combination of surgical and medical therapy, together with proper dietary management, offers the greatest chance to control clinical signs and prolong survival time (8,9) in dogs with this malignant islet-cell pancreatic tumor.

  1. Kintzer PP. Insulinoma and other gastrointestinal tract tumours. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association; 2012:148-155.
  2. Goutal CM, Brugmann BL, Ryan KA. Insulinoma in dogs: a review. J Am Anim Hosp Assoc 2012;48:151-163.
  3. Bell SJ, Forse RA. Nutritional management of hypoglycemia. Diabetes Educ 1999;25:41-47.
  4. Conn JW. The advantage of a high protein diet in the treatment of spontaneous hypoglycemia. Preliminary report J Clin Invest 1936;15:673-678.
  5. Blumberg S. Should hypoglycemia patients be prescribed a high-protein diet? J Am Diet Assoc 2005;105:196-197.
  6. Meleo KA, Peterson ME. Treatment of insulinoma in the dog, cat, and ferret In: Bonagura JD,Twedt DC, eds. Kirk's Current Veterinary Therapy, Volume XV. Philadelphia: Saunders Elsevier, 2013.
  7. Leifer CE, Peterson ME, Matus RE. Insulin-secreting tumor: diagnosis and medical and surgical management in 55 dogs. J Am Vet Med Assoc 1986;188:60-64.
  8. Rychel J, Worley DR, Hardy CS, et al. Prolonged survival in an aged labrador retriever with a metastatic insulinoma. J Am Anim Hosp Assoc 2013;49:224-229.
  9. Polton GA, White RN, Brearley MJ, et al. Improved survival in a retrospective cohort of 28 dogs with insulinoma. J Small Anim Pract 2007;48:151-156.

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