Nutritional Management of Feline Hyperthyroidism
David Bruyette, DVM, DACVIM Medical Director, VCA West Los Angeles Animal Hospital, Los Angeles, Calif.
Claudia A. Kirk, DVM, PhD, DACVIM, DACVN Professor and Head, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tenn.
J. Catharine Scott-Moncrieff, MA, VetMB,MS, DACVIM, DSAM, DECVIM Professor of Small Animal Internal Medicine, School of Veterinary Medicine, Purdue University, West Lafayette, Ind.
Edward W Kanara, DVM, DABVP Managing Member Kanara Consulting Group, LLC Kennett Square, Penn.
Hyperthyroidism is the most common endocrine disease of cats worldwide. It is most often associated with a benign thyroid tumor that produces excessive thyroid hormone. Options for managing hyperthyroid cats have included thyroidectomy, radioactive iodine therapy, and anti-thyroid drugs. Recently, using a limited-iodine food (Hill’s® Prescription Diet® y/d Feline Thyroid Health) was introduced as another option for managing hyperthyroidism in cats.
A panel of experts discussed the role of nutritional management of feline hyperthyroidism and answered key questions from attendees of a symposium on Feline Hyperthyroidism held at the Western
Veterinary Conference in Las Vegas, Nev., February 22, 2012. The panel was moderated by Dr. Edward Kanara.
Dr. Kanara: When should nutritional management with Prescription Diet y/d be recommended for hyperthyroid cats and how do you select patients for this option?
Dr. Bruyette: We approach it just like any other disease – we give the owner the various choices, talk to them about medication (oral and topical) versus nutritional management and radioactive iodine. There’s a treatment that’s hopefully best for each particular cat and their owner; we try to help them decide what’s best for them in terms of treating the cat, with the caveat that if they opt for anti-thyroid drugs or nutritional management first and it’s not working or they’re not happy with it, we’ve got other ways to treat the cat.
Dr. Kanara: Should you recommend nutritional management of hyperthyroidism in cats that have concurrent diseases?
Dr. Kirk: Early on when a limited-iodine food was in initial investigation, one of the first things noted was a reduction in serum creatinine and improvement in renal parameters. And you certainly could look at that and say, well, it’s a lower protein food. But the food is similar in protein concentration when compared with other standard maintenance pet foods on the market So it’s not really a protein-restricted food but the nutrient values are very renal friendly. So in terms of managing concurrent kidney disease, I think that it’s actually a very good option. From a compatibility standpoint, I think the food (Prescription Diet y/d Feline) will work well for cats with kidney disease and hyperthyroidism, and the data support that early on.
Dr. Kanara: So let’s follow up with a different question. What amount of protein should be fed to meet the needs of a hyperthyroid cat, including maintenance of muscle mass?
Dr. Ki rk: There are no data on the protein require ment in hyperthyroid cats. The only data that’s out there, that I’m aware of, is about digestibility of pro tein with aging, and it does show that very geriatric cats have a reduction in protein digestibility. And so there’s been a lot of discussion that old cats need very high protein pet foods because of that. But there certainly are no data that support that higher protein pet foods increase longevity and reduce disease incidence in older cats. I think the data in cats with kid ney disease support that 3.5 g of protein per 100 kcal is sufficient to maintain health. The amount of protein in y/d Feline is more than adequate. It provides somewhere between 8 and 9 g per 100 kcal. That’s considered a high-protein food in our Intensive Care Unit when we’re using total parenteral nutrition (TPN), and I’m pretty comfortable that’s a sufficient food for hyperthyroid cats.
Dr. Kanara: If a veterinarian has opted to transition a hyperthyroid cat from anti - thyroid drugs to nutritional management, what’s the best way to do that? What are the considerations that a practitioner needs to take into account?
Dr. Scott-Moncrieff: My experience is based on four or five cats that were having problems with methimazole. My approach has been to stop methimazole and then start the transition to y/d. I think that has worked for me and I haven’t had any issues with immediate methimazole withdrawal. We’ve always discontinued methimazole for 1 to 2 weeks before radioactive iodine treatment and have never run into any problems. I think that makes more sense because I worry about the potential for making these cats hypothyroid, and I worry more about hypothyroidism than I do about hyperthyroidism. I don’t think that you need to worry about thyroid storm. I’m not convinced that it really happens in cats.
Dr. Kanara: Is it okay to feed y/d to healthy cats in a multi-cat household? And, if so, what considerations do you advise owners in multi -cat households?
Dr. Kirk: Owners have difficulty feeding a single pet food or a single quantity to one cat so it’s a challenge. I think feeding all cats in the household a single food makes it easier to keep the one cat that’s hyperthyroid on its food. What has been recommended by Hill’s is to feed a small amount (1 tablespoon, dry or wet) of a life-stage appropriate food on a daily basis, because we know that very minor amounts of different foods with higher iodine concentrations are going to meet the needs of those cats. So from a practical stand point, I think that’s going to be the most rational thing to do because it’s very difficult to feed a single cat in a multi-cat household.
Dr. Kanara: In closing, please share the one or two take-home messages or key points you’d like to leave with practitioners regarding nutritional management of feline hyperthyroidism?
Dr. Scott-Moncrieff: What I would say is that nutritional management is now another option for management of hyperthyroid cats. I think the most important thing that I would like people to remember is that every cat is going to be different. I think that for younger cats, or an owner who can afford definitive therapy with radioactive iodine, that should be the number one consideration. I think that y/d is another option for cats that cannot be treated with radioactive iodine and that do not tolerate methimazole. I think over time, we’re going to figure out how many cats will do really well long term with this pet food.
I hope there will be ongoing discussions as we accumulate case experiences with this option. This is what we know right now. In a couple of years, I think we’ll know a lot more, and we’ll be able to give people better guidelines about which are the best cases for recommending nutritional management. But as I said, I’ve treated four or five cases, and I’ve been really happy with the cases that I’ve had experience with. It’s really given the owners options that they didn’t have before.