By By Marissa Heflin
The most common concurrent condition is chronic kidney disease, said Lynda Melendez, DVM, medical director of clinical research at Hill’s Pet Nutrition of Topeka, Kan. About 30 to 40 percent of cats with feline hyperthyroidism also have chronic kidney disease, she said. The most common concurrent condition is chronic kidney disease, said Lynda Melendez, DVM, medical director of clinical research at Hill’s Pet Nutrition of Topeka, Kan.
Veterinarians have had nutrition as a new tool for managing feline hyperthyroidism for a little more than six months. Previously, veterinarians typically relied on radioactive iodine, thyroidectomy or anti-thyroid drugs, options that can prove expensive and have varied side effects.
Nutrition can also be useful in managing concurrent diseases associated with hyperthyroidism, according to Hill’s Pet Nutrition Inc., which launched its Prescription Diet y/d Feline Thyroid Health in both dry and wet formulations late last year.
The most common concurrent condition is chronic kidney disease, said Lynda Melendez, DVM, medical director of clinical research at Hill’s Pet Nutrition of Topeka, Kan. About 30 to 40 percent of cats with feline hyperthyroidism also have chronic kidney disease, she said.
“Since [both are geriatric diseases], it’s not at all surprising that the two show up together,” Dr. Melendez said.
In fact, Hill’s took into consideration the nutritional needs of cats with chronic kidney disease when developing y/d Feline, Melendez said.
“When we were making [y/d Feline], we recognized that these were older cats,” she said. “In general, our philosophy for senior cats is to make foods a little more friendly to the kidneys. … [y/d Feline] was made for older cats that probably have kidneys that are not 100 percent anymore.”
Similar to therapeutic renal foods, y/d Feline has controlled amounts of protein, phosphorous and sodium and is supplemented with omega-3 fatty acids.
Although y/d Feline has a moderately reduced amount of protein (about 27 percent to 28 percent on a caloric basis) compared to other adult cat foods, it still has a higher protein content than Prescription Diet k/d Feline Renal Health, said David Bruyette, DVM, Dipl. ACVIM.
Dr. Bruyette, medical director at VCA West Los Angeles Animal Hospital, uses y/d Feline in his hyperthyroid feline patients. Hill’s Pet Nutrition had invited Bruyette to use y/d Feline in some of his patients as before the product was launched.
Historically, he said, cats with renal disease have been put on protein-restricted nutrition, he said.
“One of the concerns is that if you have cats with concurrent renal disease and you switch them from a lower protein food to something like y/d, will that have an adverse effect on kidney function?” Bruyette said.
Bruyette said it’s too soon to know the answer, although he said that so far he hasn’t seen any decrease in renal function.
“What we have seen is that as we controlled the thyroid level, the renal disease actually got better, or it didn’t get worse,” he said.
Other Concurrent Diseases
Diabetes mellitus is another common concurrent disease of hyperthyroid cats, according to both Melendez and Bruyette.
Since nutritional therapy is a cornerstone of the management of cats with diabetes, using y/d Feline for cats with this concurrent disease may be a viable option, Melendez said.
Research indicates that foods that contain 5 to 26 percent of calories from carbohydrates help maintain glycemic control in diabetic cats, according to Hill’s. The percent of calories from carbohydrates in y/d (23 percent dry, 24 percent canned) is within this range.
“[y/d Feline] falls within what the evidence shows is a friendly food for diabetes,” Melendez said. “So we think, for some cats at least, that this is a decent food.”
Depending on the cat, additional therapies such as insulin may still be needed, Melendez noted.
However, when it comes to protein content, diabetes is sort of the opposite of chronic kidney disease, Bruyette said.
When a cat has diabetes, the recommendation is usually to go to a canned food that is high in protein and low in carbohydrates, he said.
“Y/d is not a high protein food, so the concern is, would it adversely affect a diabetic cat’s regulation if we switched him from his current food to a food like y/d? Again, we don’t know,” he said.
Bruyette’s current recommendation: If a cat with hyperthyroidism is doing clinically well on y/d and then develops diabetes, switch to y/d canned food and start the cat on insulin. Monitor the cat for two months and see if the diabetes goes into remission. If it does, then it isn’t necessary to change the food, but if doesn’t, switching to a higher protein, low carb food is called for.
A third common concurrent disease is inflammatory bowel disease. Although it’s common, it’s hard to get actual numbers because it is often diagnosed through a physical examination and not a blood test that records such data, Bruyette said.
Unlike chronic kidney disease and diabetes mellitus, inflammatory bowel disease is not about the amount of protein but the source of protein, the doctor said. Cats with inflammatory bowel disease are typically put on a novel protein food, such as duck, rabbit, lamb, venison or fish.
“So the question is, if you have a cat that has inflammatory bowel disease that’s been doing well on a novel protein and then gets hyperthyroidism, would its GI tract be adversely affected if the food is changed to y/d because it’s not a novel protein source? And again, we don’t know,” Bruyette said.
However, Bruyette noted that medication to control hyperthyroidism may cause more GI upset than switching the food.
A Balancing Act
In the end, veterinarians must weigh the pros and cons of managing each disease and decide which one has the greatest effect on longevity and quality of life.
“I always tell veterinarians, take a look at your patient, figure out the thing that is affecting its quality of life the most and do the best for that particular disease process,” Melendez said.
For instance, if a diabetic cat needs fewer carbohydrates, y/d may not be the best option, she said.
Melendez said she understands that this process can be difficult to sort through, but that’s where talking with a vet consultation service or other vets who have had similar patients can be helpful.
Chances are that if the cat being managed doesn’t already have a concurrent illness, Bruyette said, as time progresses, it will.
“The good news is, with hyperthyroid cats, you have many options,” he said. “The bad news is, you have many options. There’s not one treatment for all cats. You’ve got lot of good options, which is fortunate, but you have to match the treatment with the cat and the owner. Figure out what the owner is comfortable with and what they want to do financially and what the cat will tolerate.”
