Animal Endocrine Clinic: y/d

Showing posts with label y/d. Show all posts

Tuesday, December 17, 2013

Using a Low-Iodine Diet (y/d) in Hyperthyroid Cats Allowed Outdoors

Is feeding the low-iodine diet (Hill's y/d) an appropriate or reasonable choice for a hyperthyroid cat that is allowed outside and hunts?

Will the diet work to control the hyperthyroid state if the cat eats small prey?

My Response:

No, Hill's y/d would not work to lower the high serum T4 and T3 in a cat in this situation.

All species (cattle, pigs, chickens, birds, mice and other rodents) all contain iodine in their muscle tissue (1,2). Iodine may be ingested in the diet as a supplement, but it's also present in soil, which ends up in the plants ruminants and other animals may eat (3,4). Remember that iodine is an essential nutrient and is needed by all animals (including humans!).

This cat, by eating birds and rodents (not eating an iodine deficient diet, of course), would ingest too much iodine for the y/d to be effective. To lower T4 secretion, the diet has to be very, very low in iodine.

References:

Hemken RW. Factors that influence the iodine content of milk and meat: a review. Journal of Animal Science 1979;48:981-985.
Downer JV, Hemken RW, Fox JD, et al. Effect of dietary iodine on tissue iodine content in the bovine. Journal of Animal Science 1981;52:413-417.
Whitehead DC. Studies on iodine in British soils. Journal of Soil Science 1973;24:260-270.
Fuge R, Johnson CC. The geochemistry of iodine — a review. Environmental Geochemistry and Health 1986;8:31-54.

Saturday, October 26, 2013

Can a Special Diet be Formulated to Treat Hyperthyroidism in Cats?

I have a 13-year old female DSH cat that has recently been diagnosed with hyperthyroidism. Unfortunately found out that she is severely allergic to methimazole (severe vomiting and anorexia), so I cannot treat her with medication (even though I've read this medicine can cause other health issues).

My next option was to feed her the Hill's y/d diet, but she absolutely refuses to eat that food. I then began an online search to see if I could make my own low-sodium cat food that would mimic the Hill's diet. My online research brought me to your blogs about hyperthyroidism and diet.

After reading many of your blogs, I found where you say that a high protein/low carb diet is beneficial to the hyperthyroid cat (http://endocrinevet.blogspot.com/2011/09/best-diet-to-feed-hyperthyroid-cats.html), but it doesn't address sodium content.

Do you believe a diet referenced in your blog would be a life-long treatment for a cat with hyperthyroidism? Or should I pay a veterinary nutritionist to compose a diet for my cat with an iodine level at or below 0.32 ppm (www.2ndchance.info/lowIodine.htm), which Hill's y/d diet allows? I recently called the nutritionists at UC Davis about such a diet, but was told that they have never made a diet for hyperthyroidism in cats.

I've also read that too low of sodium in a cat's diet will cause the thyroid to once again over-produce hormones to compensate. To say the least, I'm confused. I'm at a crossroad wondering if I should try a diet or go ahead and have the I-131 treatment done for my cat.

Thank you so much for your opinion and response.

My Response:

High protein, low-carbohydrate diet for hyperthyroid cats
First of all, my recommendation to feed hyperthyroid cats a diet higher in protein and lower in carbohydrates is based on what we know about the secondary complications of hyperthyroidism.

Hyperthyroidism is a hypermetabolic, catabolic state. Therefore, in hyperthyroidism, the body may be forced to use it's own muscle tissue to supply increased energy it needs. Because of these increased protein needs of the hyperthyroid cats, loss of lean body mass and muscle wasting is common. By adding more protein to the diet, this will help preserve or restore lost muscle mass, but feeding a high protein diet, by itself, will do nothing to lower thyroid hormone secretion or correct hyperthyroidism.

My recommendation for feeding hyperthyroid cats a low-carb diet is based on the fact that hyperthyroid cats commonly develop a form of prediabetes. Feeding a lower carb diet will help prevent the onset of overt diabetes in these cats. Even if this was not true, cats have absolutely no dietary requirement for carbohydrate and cats in the wild would normally ingest only 1-2% of their daily calories in the form of carbs (1). But again, limiting the amount of carbohydrates in a hyperthyroid cat's diet would do nothing to treat the hyperthyroid condition.

Overall, a diet higher in protein and lower in carbs, is actually a more "natural" diet for cats (1,2). But this natural diet fed to hyperthyroid cats must be combined with another treatment directed specially at the thyroid gland (e.g., antithyroid drugs, surgical thyroidectomy, or radioiodine).

Salt and the thyroid
In cats, both sodium and chloride (i.e., salt) are required in relatively small amounts in the diet. Nutritional requirements for dietary salt in cats are available from regulation associations or scientific councils, mostly based on studies establishing sodium requirements in cats (3,4). Salt restriction has been historically advocated for cats in some disease states (mainly cardiovascular and kidney diseases) (5,6). No study has confirmed the benefit of such dietary intervention in cats.

However, feeding a cat a low sodium (or salt) diet will not do anything to lower thyroid hormone secretion from the thyroid gland. In other words, we have no evidence at all that a low salt diet can be used as a treatment for hyperthyroidism. Now, because iodine is commonly added to salt as a treatment for iodine deficiency (7,8), using a lower salt diet could lower iodine levels very slightly.

Iodine and the thyroid
The y/d diet made by Hill's (named, Prescription Diet y/d Feline –Thyroid Health) is an iodine deficient diet (9-11). Unlike sodium or chloride, iodine is one of the essential building blocks needed for thyroid hormone synthesis.

The main thyroid hormones secreted by the feline thyroid include thyroxine (T4) and triiodothyronine (T3). If we look at the thyroxine molecule, it contains four atoms of iodine per molecule, and that's how the common abbreviation "T4" was derived. Triiodothyronine contains one less iodine atom, thus the common abbreviation "T3." Therefore, it's the number of iodine atoms in each of these thyroid hormones that determines the "number" in T4 or T3.

The basis for using a severely restricted iodine diet to treat hyperthyroid cats is that iodine is an essential component of both T4 and T3. With severe dietary iodine deficiency, the thyroid cannot produce adequate amounts of thyroid hormone (8,9).

Hill's y/d is clearly an iodine deficient diet, containing levels of approximately 0.2 mg/kg (0.2 ppm) on a dry matter basis, well below the minimum daily requirement for adult cats (0.46 mg/kg or 0.46 ppm) of food (9-11). Our current data does indicate that feeding y/d, a diet severely restricted to overtly deficient in iodine, will result in normalization of T4 levels in most hyperthyroid cats. Since iodine is an essential nutrient and has other functions other than making T4 and T3 (12), the long-term effects of such iodine deficiency in cats remains unclear.

Can a low-iodine home-made diet be formulated?

I am well aware of the claim by some, including Dr. Hines, that it is possible to make your own low-iodine diet. However, if this were true, then why would we ever feed the Hill's y/d diet, which is very unnatural?

You can certainly talk to a veterinary nutritionist about making an iodine-deficient diet for your cat (13). Unfortunately, it is just not that easy to formulate such a diet, and I do not know of anyone who has made one. That's especially true if we want to feed a higher protein, lower-carbohydrate diet (iodine is present is most meat, since iodine is a required nutrient in all animals, including cattle, chickens, and pigs). And remember, cats are meant to eat a low-carb, high-protein diet!

My Bottom Line:

At 13-years of age (a middle-aged senior cat), I would consider a definitive form of treatment of the hyperthyroidism to be ideal. I'd talk to your veterinarian about the possibility of the use of radioiodine or surgical thyroidectomy. Once your cat is cured, then we can concentrate on the use of nutrition to help restore any lost muscle mass and to improve glucose metabolism.

References:

Eisert R. Hypercarnivory and the brain: protein requirements of cats reconsidered. J Comp Physiol B 2011;181:1-17.
Zoran DL. The carnivore connection to nutrition in cats. Journal of the American Veterinary Medical Association 2002;221:1559-1567.
AAFCO (Association of American Feed Control Officials). Official Publication, 2007.
NRC (National Research Council). Minerals. In: Nutrient Requirements of Dogs and Cats. Washington DC, The National Academy Press, 2006:145-192.
Xu H, Laflamme DP, Long GL. Effects of dietary sodium chloride on health parameters in mature cats. J Feline Med Surg 2009;11:435-441.
Reynolds B. Dietary salt and cats: evidence-based approach. Proceedings of the 21st ECVIM-CA Congress, 2011.
Zimmermann MB. Iodine deficiency. Endocr Rev 2009;30:376-408.
Zimmermann MB, Andersson M. Assessment of iodine nutrition in populations: past, present, and future. Nutr Rev 2012;70:553-570.
Melendez LM, Yamka RM, Forrester SD, et al. Titration of dietary iodine for reducing serum thyroxine concentrations in newly diagnosed hyperthyroid cats [abstract]. J Vet Intern Med 2011 2011;25:683.
Melendez LM, Yamka RM, Forrester SD, et al. Titration of dietary iodine for maintaining serum thyroxine concentrations in hyperthyroid cats [abstract]. J Vet Intern Med 2011;25:683.
Yu S, Wedekind KJ, Burris PA, et al. Controlled level of dietary iodine normalizes serum total thyroxine in cats with naturally occurring hyperthyroidism [abstract]. J Vet Intern Med 2011;25:683-684.
Patrick L. Iodine: deficiency and therapeutic considerations. Altern Med Rev 2008;13:116-127.
Fascetti AJ, Delaney SJ. Nutritional management of endocrine disease In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. Chickester, West Sussex: Wiley-Blackwell, 2012;289-300.

Friday, March 15, 2013

Hyperthyroidism in Cats: Past and Upcoming Topics

As you know, if you have been following this blog, I've spent much of the last few months writing about the diagnosis and treatment of hyperthyroidism, the most common endocrine disorder of the cat.

For my next series of posts, I'm getting back to this series to discuss the next treatment option — namely, radioactive iodine (radioiodine; I-131), which is considered by most to be the treatment of choice for most cats suffering with hyperthyroidism. I do plan to do a series of posts on a number of issues concerning radioiodine over the next few weeks.

But before I move on to the topics of treatment of this common feline condition, I thought I'd post links to the hyperthyroid topics I've covered thus far:

My next post on feline hyperthyroidism (entitled, Treating Hyperthyroid Cats with Radioiodine: The Pros and Cons) will go up within the next week; then I'll continue with I-131 treatment issues, with a post once a week.

Friday, March 1, 2013

Muscle Wasting in a Hyperthyroid Cat Fed Hill's y/d

I have read your blog posts concening the Hill's y/d diet with much interest (1-5). We have been feeding our 13-year-old female cat the Hill's y/d diet for 6 months now. The high serum thyroid values have come down into the high-normal range and her weight loss has stopped. However, she doesn't look like the same cat as she used to be, and we have noticed her getting smaller and more bony. She eats the y/d, but not with the same gusto as she used to eat when we fed her regular OTC canned foods.

Is this the muscle wasting you talk about in your blogs? Should we change her treatment and put her on medication in order for her to have a more balanced diet?

Although she is not very old, the procedures listed to "cure" hyperthyroidism look like they may be risky. We don't want our cat to undergo anesthesia or have surgery. Is the radioactive treatment dangerous to our cat's health? What does the radioiodine procedure involve? Is it expensive? Does this procedure make it dangerous to handle the cat litter for awhile?

We want my cat to live a long and happy life, but it looks like she won't be able to keep going very long if we keep her on this diet! Thanks for your advice.

My Response:

Muscle wasting and protein needs in older cats
I agree that it is likely that your cat looks "smaller" because of the loss of muscle mass that can occur in hyperthyroid cats if not fed enough protein (6-9). Like I discuss in my blog posts, Hill's y/d is not a high protein diet, containing less than 28% of calories as protein (1). In contrast, cats in the wild generally eat between 50-60% of their daily calories as protein.

A recent paper proves that cats, as obligate carnivores, require over 5 grams of protein each day to maintain muscle mass (10). Hyperthyroid cats would be expected to need even more protein, since hyperthyroidism is a catabolic state and it's well known that we see muscle breakdown and muscle loss with this disease (2,6,7). Putting that amount of protein into perspective, that means that we should be feed our cats a diet that contains at least 40% of their calories as protein to restore or regain lost muscle mass, an amount much greater than that contained in the y/d diet.

Best treatment for a young hyperthyroid cat without concurrent disease
In my opinion, we should try to remove or destroy the thyroid tumor in any cat that is relatively young and in good health otherwise. At 13-years of age, your cat certainly is not very old (only about 55-60 in human years). By choosing either surgery or radioiodine, we will be able to cure the thyroid disease and do not have to feed an iodine deficient diet (y/d) or use life-long, twice daily medication (9,11).

In most cats, leaving the thyroid tumor allows it to continue to grow larger and larger, and in some cats, the benign tumor can transpose into a malignant carcinoma (12). Radiodine is generally considered to be the treatment of choice. Compared to surgery, no anesthesia is needed, and we don't have to worry about parathyroid damage (the 4 little glands around the thyroid that control calcium) or possible hypocalcemia. For more information about the pros and cons of radioiodine, see my hospital website (www.animalendocrine.com). I also have a FAQ section on the website that should answer all of your questions about this treatment.

If done properly, radioiodine is not at all risky (12). At our facility, most cats only stay with us for 3-5 days. The doses of radioiodine we use are actually quite small in most cats, so their whole body radiation levels are not very high and no side effects are expected. To make it easier for you to be separated from your cat, we have even installed webcams within each of their condos so you can check-in whenever you wish.

Like you, I too want all cats to live a long and heathy life. In cats with hyperthyroidism, I believe this includes curing the disease so we can focus on proper nutrition (6,7) and environmental enrichment. By not giving life-long medication, this also reduces the cat's level of stress, which we do see in some cats that have to be chronically medicated. And what cat really wants to eat a single type of food every day for the rest of their lives?

References:

Peterson ME. Is Hill's y/d a nutritious diet for hyperthyroid cats? Insights into Veterinary Endocrinology. September 28, 2011.
Peterson ME. Optimal protein requirements for older cats and cats with hyperthyroidism. Insights into Veterinary Endocrinology. November 7, 2011.
Peterson ME. Is the protein content of Hill's y/d too low to restore and maintain muscle mass in cats with hyperthyroidism? Insights into Veterinary Endocrinology. November 10, 2011.
Peterson ME. Can increasing the amount of fat or carbohydrate in a cat's diet compensate for low protein intake? Insights into Veterinary Endocrinology. December 22, 2011.
Peterson ME. Is it feasible for older cats to ingest the optimal amounts of protein they need each day? Insights into Veterinary Endocrinology. December 14, 2011.
Peterson ME. Nutritional management of endocrine disease in cats. Proceedings of the Royal Canin Feline Medicine Symposium 2013; 23-28 2013;23-28.
Peterson ME. The best diet to feed hyperthyroid cats. Insights into Veterinary Endocrinology. September 13, 2011.
Sparkes AH. Feeding old cats— An update on new nutritional therapies. Topics in Companion Animal Medicine 2011;26:37-42.
Baral R, Peterson ME: Thyroid gland disorders, In: Little, S.E. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders. pp. 571-592, 2012.
Laflamme DP, Hannah SS. Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats. J Fel Med Surg 2013; in press.
Peterson ME, Broome MR. Radioiodine for hyperthyroidism. In: Bonagura JD, Twedt DC (eds): Current Veterinary Therapy V. Philadelphia, Saunders Elsevier, 2013; in press.
Peterson ME, Broome MR. Hyperthyroid cats on long-term medical treatment show a progressive increase in the prevalence of large thyroid tumors, intrathoracic thyroid masses, and suspected thyroid carcinoma. J Vet Intern Med 2012;26:1523.

Monday, February 4, 2013

Should Hill's y/d Diet Ever Be Used to Manage Cats with Hyperthyroidism?

Hyperthyroid cat with an allergic reaction (facial pruitus) secondary to methimazole

We are unlikely enough to have not one... but two cats with hyperthyroidism. One has responded well to treatment with methimazole, with normalization of the serum T4 value, while the other cat had a severe allergic reaction (facial pruitus) so we had to stop the medication. Because of her age and how ravaged she was by the allergic reaction, we didn't want to do radiation or surgery.

My veterinarians suggested that we could try Hills' y/d diet, since no other good options were available. Since we had no other options available, we felt that we had nothing to lose. Luckily, our cat will eat the diet. Slowly, she has improved and is doing fairly well.

Who knows if this food will be good for her long term (I take your comments seriously about what cats truly need in their diet), but she's almost 16-years old and has enjoyed a good life. Considering our situation, trying the diet was worth a shot, and it has lowered the serum T4 value to normal.

Now I'm feeling guilty — should I continue the y/d or should I rethink my decision not to use the radioiodine?

My Response:

I consider the feeding of Hill's y/d diet to be a fourth-line of treatment for hyperthyroidism; I'd recommend this treatment only if none of the 3 other options (i.e., radioiodine, surgical thyroidectomy, or methimazole) can be used (1-3).

If a hyperthyroid cat will eat this ultra-low iodine food (and not eat anything else), the y/d certainly will lower the serum thyroid hormone concentrations (4). Remember that iodine is an essential nutrient and is needed to make thyroid hormone; with this diet, we are inducing an iodine deficient state so the cat's thyroid tumor will not be able to continue to produce large amounts of thyroid hormone on this diet (5).

However, like methimazole, feeding an ultra-low iodine diet can not cure the primary cause of hyperthyroidism (ie, the thyroid tumor). The thyroid tumor, which is almost always benign at time of diagnosis) will continue to grow with time (5,6). In some cats, this benign tumor can also transform to a more malignant carcinoma after a few months to years. So whenever possible, I believe it's always better to remove the thyroid tumor with surgery or ablate it with radioiodine —in that way, we are curing rather than prolonging the disease and not allowing the thyroid tumor to continue to grow.

Now, if you consider 16 year's of age too old for definite treatment, then y/d can certainly be fed. For a geriatric cat, I don't consider 15 or 16 years of age too old for definitive treatment unless other concurrent problems are present that are known to shorten their lives. Remember that old age itself isn't a disease, and I see many senior cats that are still doing well at 18 to 20 years of age.

The main advantage of the methimazole over the y/d is that we can control what the cat is fed (remember that cats managed with y/d can ONLY eat that diet). The best diet for a hyperthyroid cat or any senior cat for that matter is one that is lower in carbohydrates (<15% of calories) and higher in protein (>35-40% of calories) (7). Senior cats don't absorb protein as well as younger cats and will develop weight loss and muscle wasting as they age (8-11). Other than exercise (and good luck with getting most cats to enter a weight lifting regime), the best way we know to maintain muscle mass is to feed a higher protein diet.

When we look at the dietary composition of Hill's y/d, it's way too high in carbs (>23% of calories), and much too low in protein (<28% of calories). In addition, the protein that's contained in the dry y/d is all plant protein, which isn't as good as animal protein is for cats — when was the last time you heard of a feral cat that was a vegetarian?

Obviously, in your cat, we can never use methimazole again because of the severe allergic reaction that occurred. So, should you continue the y/d for your cat? That's a decision that you will have to make— remember that any treatment, including the y/d, is better than no treatment at all.

But I like to treat the whole animal, however, and that involves more than just giving pills, feeding an iodine-deficient diet, or even giving an injection of radioiodine. For me, that involves proper geriatric nutrition, supplements in some cats, and finally, environmental stimulation to help enrich their lives (1-3, 7).

References:

Mooney CT, Peterson ME. Feline hyperthyroidism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association. 2012;92-110.
Baral RM, Peterson ME. Thyroid gland disorders In: Little SE, ed. The Cat: Clinical Medicine and Management. St. Louis: Elsevier Saunders, 2012;571-592.
Peterson ME. Hyperthyroidism in cats In: Rand JS, Behrend E, Gunn-Moore D, et al., eds. Clinical Endocrinology of Companion Animals. Ames, Iowa Wiley-Blackwell, 2013;295-310.
Yu S, Wedekind KJ, Burris PA, et al. Controlled level of dietary iodine normalizes serum total thyroxine in cats with naturally occurring hyperthyroidism [abstract]. J Vet Intern Med 2011;25:683-684.
Peterson M. Hyperthyroidism in cats: What's causing this epidemic of thyroid disease and can we prevent it? J Feline Med Surg 2012;14:804-818.
Peterson ME, Broome MR. Hyperthyroid cats on long-term medical treatment show a progressive increase in the prevalence of large thyroid tumors, intrathoracic thyroid masses, and suspected thyroid carcinoma. J Vet Intern Med 2012;26:1523.
Peterson ME. Nutritional management of endocrine disease in cats. Proceedings of the Royal Canin Feline Medicine Symposium 2013; 23-28 2013;23-28.
Teshima E, Brunetto MA, Vasconcellos RS, et al. Nutrient digestibility, but not mineral absorption, is age-dependent in cats. J Anim Physiol Anim Nutr (Berl) 2010;94:e251-258.
Sparkes AH. Feeding old cats--an update on new nutritional therapies. Top Companion Anim Med 2011;26:37-42.
Perez-Camargo G. Feline decline in key physiological reserves implications for mortality. Proceedings of the Nestlé Purina Companion Animal Nutrition Summit: Focus on Gerontology 2010;6-13.
Freeman LM. Cachexia and sarcopenia: emerging syndromes of importance in dogs and cats. J Vet Intern Med 2012;26:3-17.

My Related Posts on Hill's y/d Diet (Insights into Veterinary Endocrinology Blog)

Sunday, August 26, 2012

Thyroid Tumors Grow Progressively Larger in Most Hyperthyroid Cats Treated with Methimazole

As I discussed in my last post (Managing Hyperthyroid Cats That Become Unresponsive to Methimazole), methimazole blocks thyroid hormone secretion from a hyperthyroid cat's thyroid tumor (usually a benign tumor). However, in cats treated with methimazole, it is quite common for hyperthyroid cats on methimazole treatment to need higher dosages of methimazole over time, as the thyroid adenoma continues to grow larger and increases its secretion of thyroid hormone (1-3).

No one has yet studied the long-term effects of nutritional management with a low-iodine diet (i.e., Hill's y/d) on thyroid tumor growth in these hyperthyroid cats. However, the same progressive growth of the thyroid tumor would be expected on a low-iodine diet, since the thyroid tumor remains and is free to continue to grow progressively larger with time.

Figure 1: Hyperthyroid cat who has developed a very large thyroid tumor after 3 years of methimazole treatment. Notice the swollen neck, which turned out to be a massive thyroid carcinoma.

After months to years of methimazole treatment, many of these cats will develop a very large, palpable thyroid tumor (Figure 1) and will become difficult to regulate, even with high daily doses of oral or transdermal methimazole (3-5). Some cats eventually become completely refractory to methimazole, so alternative treatment modalities must be considered.

With enough time and as the disease progresses, the benign thyroid adenoma characteristic of early feline hyperthyroidism can also transform into malignant thyroid carcinoma in some cats (5,6). Again, methimazole or other antithyroid drug therapy (including Hill's y/d) does nothing to the thyroid tumor pathology and cannot stop this from happening.

Radioiodine therapy can be used to successfully treat cats with all sizes of benign and malignant thyroid tumors, but is best used on cats with small benign tumors. Cats with small thyroid tumors are easier to cure with lower radioiodine doses, resulting in shorter hospitalization times.

Video Animation: Thyroid Growth on Methimazole

The animation below describes the continued growth of the initially benign thyroid tumors causing hyperthyroidism in cats during their medical management with methimazole (Tapazole).

This video was done by my colleague and friend, Dr. Michael Broome, Director of Advanced Veterinary Medical Imaging in Orange Country, California. We have been long-term collaborators on clinical research issues pertaining to cats with hyperthyroidism, and we continue to work closely together on this common disorder (4,5).

References:

Mooney CT, Peterson ME. Feline hyperthyroidism. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association; 2012:92-110.
Baral R, Peterson ME. Thyroid gland disorders. In: Little, S.E. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders 2012;571-592.
Peterson ME. Treatment of severe, unresponsive, or recurrent hyperthyroidism in cats. Proceedings of the 2011 American College of Veterinary Internal Medicine Forum. 2011;104-106.
Peterson ME, Broome MR. Thyroid scintigraphic findings in 917 cats with hyperthyroidism. Journal of Veterinary Internal Medicine 2012; 26:754.
Peterson ME, Broome MR. Hyperthyroid cats on long-term medical treatment show a progressive increase in the prevalence of large thyroid tumors, intrathoracic thyroid masses, and suspected thyroid carcinoma. Proceedings of European College of Veterinary Internal Medicine; 2012.
Hibbert A, Gruffydd-Jones T, Barrett EL, et al. Feline thyroid carcinoma: diagnosis and response to high-dose radioactive iodine treatment. Journal of Feline Medicine and Surgery 2009;11:116-124.

Saturday, July 21, 2012

Hyperthyroidism in Cats: Past and Upcoming Topics

As you know, if you have been following this blog, I've spent much of the last few months writing about issue of hyperthyroidism, the most common endocrine disorder of the cat.

Unfortunately, I got sidetracked and have not yet finished discussing all of the treatment options that we have for management of this common problem. However, I do plan to finish up this series of topics over the upcoming weeks.

But before I move on to the topics of treatment of this common feline condition, I thought I'd post links to the topics I've covered thus far:

I'll be posting my next post on feline hyperthyroidism (entited, Antithyroid Drug Treatment for Hyperthyroidism: Brand Name, Generic, or Compounded Drug?) within the next couple of days; then I'll continue with treatment issues, with about a post once a week.

Saturday, May 12, 2012

Can a New Thyroid Health Food (Hill's y/d) Live Up to the Hype?

Can a New Thyroid Health Food Live Up to the Hype?

A new prescription cat food promises to treat hyperthyroidism in cats.
Maybe so, if the studies pan out. Where are those studies, anyway?

Dr. Eric Barchas
www.catster.com
May 3, 2012

In the blog post entitled, Can a New Thyroid Health Food (Hill's y/d) Live Up to the Hype?, Dr. Eric Barchas provides us with a good overview of what's wrong with all the hype associated with Hill's y/d diet.

As Dr. Barchas states in the beginning of his post (1): "For months, every veterinary publication I receive has been plastered with full-page advertisements for a new prescription cat food...... The new cat food is called Hill's y/d —or, more formally, Hill's® Prescription Diet® y/d™ Feline Thyroid Health on the company's website. Call me old-fashioned, but I am naturally suspicious of any food that has two ®s and a ™. Might the diet be more marketing ploy than medical breakthrough?"

For those of you who have followed my rants about what's wrong with Hill's y/d diet (2,3), you would be able to predict that this post made me smile.

So what's this diet all about and what's the problem with it?

First of all, Hill's y/d diet certainly does offers another treatment option for hyperthyroid cats. The basis for how the diet works to control the hyperthyroid state is by severely limiting the amount of iodine in the y/d (the diet is actually iodine deficient).

Because thyroid hormone contains large quantities of iodine, the diet should reduce secretion of the hormone. Indeed, the clinical experience of practicing veterinarians to date indicate the this diet is effective in lowering serum T4 values in many hyperthyroid cats, although not always to levels that we would consider "low enough."

The biggest concerns are in regard to the long-term side effects of feeding an low iodine or iodine deficient diet to cats. For y/d to work, no other food can be fed for the rest of the cat's life — so the y/d diet, if successful, would potentially be fed for years to a cat suffering from hyperthyroidism.

As Dr. Barchas points out in his post, large, long-term safety studies are needed to determine what happens when cats with or without thyroid disease eat y/d months to years. Now I know it seems difficult to believe, but adequate long-term safety studies of cats fed this diet have yet to be done.

Because Hill's y/d is not a drug (although it's certainly being marketed as a replacement for methimazole), the company is not required to do long-term safety studies. And it's fairly clear that they have no intention of paying to have them done.

The bottom line:

Again, Dr. Barchas says it better than I could do so let me quote the summary for his post (1): "In short, I believe that Hill's has unleashed y/d with too little research and too much hype. The food may turn out to be a veritable godsend, or it could be a disaster. Only time, and more studies, will tell....

For now, no matter how many fancy ads I see, I am hesitant to recommend the food unless a cat absolutely is not a candidate for any of the other three hyperthyroidism treatments."

Related links:

To read the complete post by Dr. Barchas, click this link.
To read my posts on y/d on the Animal Endocrine Clinic blog, click this link.
To read my posts on y/d on the Insights into Veterinary Endocrinology blog, click this link.

Sunday, April 1, 2012

Steve Dale Interviews Dr. Peterson About Treatment Options for Feline Hyperthyroidism

Dr. Mark Peterson was recently interviewed by Steve Dale about the options available for treating feline hyperthyroidism.

You may click through to subscribe to the Animal Endocrine YouTube Channel, as well as Steve Dale's YouTube Channel, to keep on top of new video uploads. Dr. Peterson and the Animal Endocrine clinic can also be followed on our Animal Endocrine blog, our blog for vets, our website, on Facebook and on Twitter.

Tuesday, January 10, 2012

Dr. Mark Peterson Interviewed for "My Pet World" News Column About Treating a Geriatric Hyperthyroid Cat

My Pet World: Advice from the Experts

By Steve Dale, Tribune Media Services

Q: The thyroid levels for my 21-year-old cat have recently become elevated, indicative of early stage hyperthyroidism. My veterinarian recommended a prescription diet (Hill's prescription y/d) or transdermally administered methimazole. The veterinarian believes radioactive iodine is a bit too extreme for a cat of this age.

I'm worried that my cat will find the (prescription) diet unpalatable. I'm also concerned about the side effects of transdermal medication. I'm impressed with what I've read about a natural solution called Resthyro. What's your opinion on what I should do for my feisty geriatric cat? -- N.M., Highland Park, IL

A: Dr. Mark Peterson, of New York City, is one of the world's experts on this topic, and helped create the radioactive iodine treatment you mention. Hyperthyroid disease nearly always occurs in older cats. Still, he says he understands that with a cat as elderly as yours, there are limits on what it makes sense to do. "I can see where this cat is no candidate for radioactive iodine," he commented. This treatment typically cures hyperthyroid disease, and is benign, but takes the cat away from home for several days of treatment.

Peterson says he doesn't personally see many adverse reactions to transdermal medication (delivering medication through the skin rather than a pill) for hyperthyroid disease. And he's seen a lot of hyperthyroid cats. Of course, side effects can potentially occur with any medication, but sometimes what you read on the Internet may be skewed. The pill version of methimazole may be just fine, but you no doubt know it can be hard to convince a cat to take a pill, which is why the transdermal might be preferred.

As for the new Hills prescription y/d diet, Peterson says, "It's long-term safety for real use is unknown." He's not absolutely convinced about the diet, and agrees that any diet change might be a problem for a 21-year-old pet. Still, that's a possible option.

As for Resthyro, Peterson said he has not seen much success. If you want to try the "natural" route, ask your veterinarian about L-Carnitine (a nutritional supplement available wherever vitamins and supplements for people are sold). Peterson says if your cat is mildly hyperthyroid, this may the best option worth trying, but do monitor your cat's thyroid levels. Open the capsule and sprinkle the contents on your cat's food or a special treat, such as a bit of chicken. Try starting at 250 mg daily.

Links to Original Article:

Chicago Tribune, http://www.chicagotribune.com/entertainment/books/sns-201112131830--tms--petwrldctnya-a20111215dec15,0,405315.story
Hartford Courant, http://www.gadzoo.com/hartfordcourant/Article.aspx?id=107094

About Steve Dale:

Steve Dale, pet expert and certified dog and cat behavior consultant, reaches more pet owners than any other pet journalist in America. Steve writes a twice-weekly syndicated newspaper column (Tribune Media Services).

He is also a contributing editor at USA Weekend and is the host of two nationally syndicated radio shows, Steve Dale’s Pet World and The Pet Minute, and Steve Dale’s Pet World at WLS Radio, Chicago. To learn more, visit Steve's website at www.stevedalepetworld.com.

Monday, November 14, 2011

Dr. Peterson Interviewed about Hyperthyroidism on PetLifeRadio

PetLifeRadio.com is the #1 pet podcast radio network, featuring weekly 30-minute talk shows hosted by the most well-known pet experts.

On Wednesday, November 10, 2011, Dr. Mark Peterson was interviewed by the Pet Doctor (Diane Levitan, DVM) concerning the latest information about hyperthyroidism in cats. To listen to this interview, click on this link to go to "The Pet Doctor" page on PetLifeRadio.com.

Episode 129:

Hyperthyroidism In Cats—A Very Common Problem with Many Options—A Must Listen Show for Anyone with Cats Over 9 Years of Age

Excerpt:
In this episode, we discuss a very common problem that happens in older cats — it’s a disease that has become much more common since the 1980s and is something that has been a difficult one to figure out. There turns out to be a good reason why older cats eat like crazy but still become very thin, they drink tons of water all the time, and their hyperactive behavior keeps their owners up at night!

It is very likely that the symptoms are due to an over-active thyroid gland, also called hyperthyroidism. There is a great deal of information on feline hyperthyroidism that has been learned in the last 20 years—what is it from? Why is it so common? What are the long-term effects on our cats and how can we prevent it?

Today we are extremely privileged to have Dr. Mark Peterson, a veterinary endocrinologist and the first in the world to publish information on this ever so common illness in cats, hyperthyroidism. He is known worldwide for his research and contributions to veterinary medicine and veterinary endocrinology and is the go to person in the world when it comes to feline hyperthyroidism and many other veterinary endocrinology topics.

Learn more about Dr. Peterson by listening and also check out his web site: www.animalendocrine.com.

Click here to listen to the interview or download it to your computer. This is a 30-minute interview. Information on nutritional management using Hill's y/d diet is discussed in the last 5 minutes.

Sunday, September 25, 2011

Treatment Options and Considerations for Hyperthyroid Cats

The underlying cause of the thyroid tumors (adenomatous hyperplasia, adenoma, or carcinoma) associated with feline hyperthyroidism is not known. Because spontaneous remission of hyperthyroidism in cats does not occur, the aim of treatment is to control the excessive secretion of thyroid hormone from the adenomatous thyroid gland.

The 4 Treatment Options

In cats, hyperthyroidism can be treated in four ways — surgical thyroidectomy, radioactive iodine (131-I), chronic administration of an antithyroid drug, or lifelong feeding of an ultra-low iodine diet. Each form of treatment has advantages and disadvantages, which must be considered when formulating the best treatment plan for the individual hyperthyroid cat.

Formulating the Best Form of Treatment for Each Cat

The treatment of choice for an individual cat depends on several factors, including the age of the cat, presence of associated cardiovascular diseases or other major medical problems (e.g., chronic kidney disease), availability of a skilled surgeon or radioiodine treatment facility, and owner's preference.

The cost of therapy is a major consideration for many cat owners. Medical treatment or use of low-iodine dietary therapy costs far less initially. However, the cost of ongoing monitoring can exceed that of thyroidectomy or radioiodine therapy over a period of many months to years.

Cure versus Control of Hyperthyroidism

Of the four forms of treatment available, it must be emphasized that only surgery and radioactive iodine remove and destroy the thyroid tumors, respectively, and thereby "cure" the hyperthyroid state.

Use of an antithyroid drug (e.g., methimazole or carbimazole) will block thyroid hormone synthesis. And chronic feeding of an iodine deficient diet will reduce the production of T4 and T3 by the thyroid tumor. However, because antithyroid drugs and low-iodine diets do not destroy the hyperthyroid cat’s thyroid tumor(s), hyperthyroidism will recur once antithyroid drugs or dietary therapy is discontinued.

Outline of Treatment

Over the next few weeks, I’ll be discussing each of the four treatment options for hyperthyroidism in some detail. In my next post, however, l will review a frequently neglected but very important part of any of the treatment options — that is, providing the hyperthyroid cat with proper nutrition and adequate amounts of water.

Hyperthyroid cats develop many muscle wasting as well as many metabolic complications because of their disease. Therefore, they have special dietary needs and require a high-quality nutrients in their daily diet including adequate amounts of water, protein, fat, vitamins, and minerals.

References

Birchard SJ, Peterson ME, Jacobson A: Surgical treatment of feline hyperthyroidism: Results of 85 cases. Journal of the American Animal Hospital Association 1984;20:705-709.
Peterson ME, Kintzer PP, Hurvitz AI: Methimazole treatment of 262 cats with hyperthyroidism. Journal of Veterinary Internal Medicine 1988;2:150-157.
Welches CD, Scavelli TD, Matthiesen DT, Peterson ME: Occurrence of problems after three techniques of bilateral thyroidectomy in cats. Veterinary Surgery 1989;18:392-396.
Peterson ME, Becker DV: Radioiodine treatment of 524 cats with hyperthyroidism. Journal of the American Veterinary Medical Association 1995;207:1422-1428.
Peterson ME: Radioiodine treatment for hyperthyroidism. Clinical Techniques in Small Animal Practice 21:34-39, 2006
Peterson ME: Hyperthyroidism, In: Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (Fifth Edition). Philadelphia, WB Saunders Co. 2000; pp 1400-1419.
Peterson ME: Hyperthyroidism in cats. In: Melian C (ed): Manual de Endocrinología en Pequeños Animales (Manual of Small Animal Endocrinology). Multimedica, Barcelona, Spain, 2008, pp 127-168.
Peterson ME: Radioiodine for hyperthyroidism. In: Bonagura JD, Twedt DC (eds): Current Veterinary Therapy XIIII. Philadelphia, Saunders Elsevier, 2009, pp 180-184.
Mooney CT, Peterson ME: Feline hyperthyroidism, In: Mooney C.T., Peterson M.E. (eds), Manual of Canine and Feline Endocrinology (Fourth Ed), Quedgeley, Gloucester, British Small Animal Veterinary Association, 2012; in press
Baral R, Peterson ME: Thyroid Diseases, In: Little, S. (ed), The Cat: Clinical Medicine and Management. Philadelphia, Elsevier Saunders, 2012; in press.
Peterson ME: Hyperthyroidism in cats, In: Rand, J (ed), Clinical Endocrinology of Companion Animals. New York, Wiley-Blackwell, 2012; in press.

about the animal endocrine clinic

The only Animal Clinic in the world devoted exclusively to diagnosis and treatment of dogs and cats with endocrine (hormonal) problems.

The Animal Endocrine Clinic is comprised of 3 subdivisions:
1) an outpatient endocrinology clinic for dogs and cats with diabetes, thyroid, parathyroid, or adrenal diseases;
2) Hypurrcat, a radioiodine treatment center for cats with hyperthyroidism; and
3) Nuclear Imaging for Animals, in which radioisotopes are used for thyroid, liver, kidney or bone imaging (scanning).