Your Thyroid: What You Need to Know

I came across this information sheet about "Your Thyroid," which came from the Hormone Health Network.  Although very simplistic, this still makes it clear that the thyroid gland and it's thyroid hormone secretion is very important for overall body function.  It also helps clarify the regulatory feedback system between the pituitary gland (secreting TSH) and the thyroid gland (secreting T4 and T3).  

For more information and fact sheets about specific thyroid diseases, click here. To learn more about other endocrine glands and their diseases, visit the Hormone Health Network website at http://www.hormone.org.

Celebrate the Seventh Annual World Thyroid Day

It's not just cats and dogs that develop thyroid disease. Approximately 750 million people worldwide are affected by thyroid disorders, and the Seventh Annual World Thyroid Day, being held this weekend, has 5 major goals, say the organizations who support it. These include the American Thyroid Association (ATA), the European Thyroid Association, the Asia Oceania Thyroid Association, and the Latin American Thyroid Society.

The thyroid gland produces hormones that regulate the body's metabolism and influence every cell, tissue, and organ in the body, they point out. Hypothyroidism is characterized by symptoms of fatigue, depression, and forgetfulness, while hyperthyroidism is associated with irritability, nervousness, and muscle weakness.

The aims of World Thyroid Day are the following:

• Increase awareness of thyroid health. 
• Promote understanding of advances made in treating thyroid diseases. 
• Emphasize the prevalence of thyroid diseases. 
• Focus on the urgent need for education and prevention programs.
• Expand awareness of new treatment modalities.

The thyroid gland, butterfly-shaped and located in the middle of the lower neck, produces hormones that influence every cell, tissue and organ in the body. The thyroid hormones regulate the body's metabolism—the rate at which the body produces energy from nutrients and oxygen—and affects critical body functions, such as energy level and heart rate.

The thyroid also plays a critical role during pregnancy, the thyroid societies explain. Consequently, the ATA recommends that pregnant women at high risk for thyroid disease should have their thyroid function tested early in their pregnancy. Another important issue is thyroid cancer, which is rapidly increasing, according to the ATA, which says there were 44,670 new cases of thyroid cancer recorded in 2010 in the United States.

But when thyroid cancer is identified and treated early, "the majority of patients can be completely cured," the American Thyroid Association stresses. The organization also notes that it is important to distinguish thyroid cancer from benign thyroid nodules, which are common in the population.

Patient education on human thyroid conditions can be found on the ATA website at http://www.thyroid.org/patient-thyroid-information/.

What's the Expected Time for Signs of Feline Hyperthyroidism to Resolve after Treatment?

My 16-year old cat was recently treated with radioiodine (I-131) for his severe hyperthyroidism. How long after radioiodine treatment will the thyroid values normalize and the symptoms of the hyperactive thyroid begin to resolve so he feels better? 

My cat lost about half of his body weight, much of it in muscle mass. Will his wasted muscles ever return to normal? If so, when can I expect to see improvement?

My Response: 

You have asked two good questions, which, on the surface seem simple enough to answer. The answers to "how long for clinical signs to resolve" however, depend on a number of factors. I'll do my best to explain why it's not possible for me to give you the definitive answers you want.

How long does it take for serum thyroid hormone levels to normalize after I-131?
Depending on the dosing protocol used, about 90% of cats will have serum thyroid hormone concentrations (e.g., T4 and T3) within reference range limits by 30 days after I-131 treatment. Most of the remaining cats will show a nice drop in T4 and T3 levels when rechecked in a month, but it will take longer to for their thyroid hormone concentrations to completely normalize.

In general, the full extent of the radioiodine treatment will be evident by 3 months after treatment, although a few cats continue to show even more (minor) improvement when rechecked at 4 to 6 months.

As the thyroid values normalize, the clinical signs we see also gradually resolve. Some signs, such as nervousness or rapid heart rate, generally resolve fairly quickly, whereas other signs, such as marked weight loss and muscle wasting, obviously take much longer.

How fast do we want the serum thyroid values to fall after radioiodine treatment?
My goal in treating hyperthyroid cats with radioiodine is to gradually normalize the high serum thyroid hormone concentrations— not lower the values too quickly. I'd rather that the thyroid values fall slowly over the first month after treatment, allowing the rest of the body to gradually get used to being euthyroid once again. This is especially true in cats with concurrent kidney disease, when a drastic fall in thyroid values can aggravate the serum kidney values and can even lead to severe renal failure.

To achieve this gradual fall in the high serum thyroid hormone levels, I administer the smallest dose necessary to cure the hyperthyroidism. By giving individualized, lower doses of radioiodine, we can also reduce the incidence of post-treatment hypothyroidism (underactive thyroid condition) in these cats.

How often does the radioiodine fail to cure the hyperthyroidism?
About 5% of cats that I treat will remain slightly hyperthyroid at the 3-month follow-up period. Many treatment facilities will claim a higher rate of cure (98-100%) than I do, which is made possible by administering higher doses of radioiodine to their cats. In addition to decreasing the incidence of persistent hyperthyroidism, the use of higher radioiodine doses will also hasten the rate of decline in the serum thyroid hormone concentrations.

So why not use this high-dose I-131 protocol instead of my lower-dose approach? Simple — the downside of administering higher radioiodine doses is that this method will lead to a higher rate of iatrogenic hypothyroidism as both the thyroid tumor, as well as most normal thyroid tissue, are irradiated and destroyed (1,2). As I've previously discussed (see my post, Estimating the Radioiodine Dose to Administer to Cats with Hyperthyroidism), more that 30% of cats will become hypothyroid using the standard high-dose treatment protocol, but this incidence could in fact be much higher, possibly up to 75%.

Diagnosing iatrogenic hypothyroidism
To monitor for iatrogenic hypothyroidism, we routinely run a serum thyroid panel (i.e., total T4, T3, free T4, and TSH) at 1 and 3 months after treatment (2,3). Most facilities recommend monitoring just the total T4 concentration, but this is not adequate for monitoring since many hypothyroid cats will maintain a low-normal total T4 value, despite being hypothyroid.  Based on our studies, it's becoming increasing clear that feline hypothyroidism can only be diagnosed by finding low to low-normal T4 and T3 values in conjunction with high TSH values.

Restoring lost body weight and muscle mass
Once euthyroidism is reestablished, most cats will gain weight within a few weeks (certainly by 2-3 months). If marked muscle wasting has occurred, it may not be possible to completely regain the lost muscle. Remember that it will help to feed a diet that's higher in protein (40-50% of calories), higher in fat (40-50% of calories), and relatively low in carbs (less than 15% of calories) (4). For more information, check out my post on The Best Diet to Feed Hyperthyroid Cats.

References:

1. Peterson ME, Broome MR. Radioiodine for feline hyperthyroidism In: Bonagura JD, Twedt DC, eds. Kirk's Current Veterinary Therapy, Volume XV. Philadelphia: Saunders Elsevier, 2014.
2. Peterson ME. Feline focus: Diagnostic testing for feline thyroid disease: hypothyroidism. Compend Contin Educ Vet 2013;35:E4. 
3. Peterson ME. Diagnosis and management of iatrogenic hypothyroidism In: Little SE, ed. August's Consultations in Feline Internal Medicine: Elsevier, 2014;in press.
4. Peterson ME. Nutritional management of endocrine disease in cats. Proceedings of the Royal Canin Feline Medicine Symposium 2013;23-28.

Related Blog Posts:

• Peterson ME. How Does Radioiodine Really Work to Treat Hyperthyroidism? Insights into Veterinary Endocrinology blog.  July 12, 2012.
• Peterson MEL Estimating the Radioiodine Dose to Administer to Cats with Hyperthyroidism. Animal Endocrine Clinic blog. April 30, 2013.
• Peterson ME. Success Rates for Radioiodine Treatment in Hyperthyroid Cats. Animal Endocrine Clinic blog. May 24, 2013.
• Peterson ME. The Best Diet to Feed Hyperthyroid Cats. Insights into Veterinary Endocrinology blog. September 13, 2011

What's the Human Risk Associated with Handling of Thyroid Medications?

Maybe I am missing something here, but I have a question about the human risk associated with handling thyroid medications. Why do you state that owners should be careful when handling and cutting methimazole tablets (Tapazole of Felimazole) because of the human safety concerns (1,2), when I can find no mention that we should use any precautions when handling or cutting L-thyroxine (L-T4) tablets?  I've heard that we should wear gloves when handling methimazole tablets or applying methimazole transdermally to the cat's ear, but no one has ever mentioned the need for gloves with L-T4 tablets.

So why is handling L-thyroxine any less of a concern than handling methimazole? Do they not both have the same potential to affect human thyroid levels? If handling methimazole can lower a human's thyroid levels, why wouldn't handling an L-thyroxine preparation potentially lead to hyperthyroidism?

My Response: 

Methimazole and L-thyroxine are totally different drugs, with different patterns of absorption and metabolism. Methimazole is a potent antithyroid drug whereas L-thyroxine is a synthetic form of natural thyroid hormone.

Methimazole
As you state, we must be careful when cutting methimazole tablets or applying transdermal methimazole since either form of methimazole could potentially be absorbed via human skin (1,2). Methimazole is a human teratogen (i.e., the drug may cause birth defects) and crosses the placenta concentrating in the fetal thyroid gland. Besides being a safety issue in pregnant women or women who may become pregnant, the drug should not be handled by lactating women because methimazole is transferred in breast milk at a high rate.

The same precautions pertain regardless of what methimazole product is used, i.e., the veterinary brand-name Felimazole preparation or a human brand-name or generic product. The methimazole tablets should not be cut with our bare hands. We want to wash our hands after administering the medication to minimize skin and oral contamination; repeated and chronic exposure could pose a risk.

L-Thyroxine
As compared to methimazole, L-thyroxine is not absorbed well from the skin. Results of two studies found that the hormone is not absorbed into the systemic circulation to have an effect on all tissues of the body (3,4). In support of that, of the few dogs that I have evaluated on transdermal L-T4, none have responded to the transdermal replacement therapy with a rise in serum T4 concentrations (5). I know that some compounded pharmacies will sell transdermal preparations of L-T4 but I do not believe that they actually work. Ask for some actual data and you will get none!

So go ahead and cut all the L-T4 pills that you want. It will not get absorbed unless you ingest the hormone supplement so you should still wash your hands to remove any residual L-T4 residue from your hands.

References:

1. Peterson ME. Methimazole-Handling Precautions for Cat Owners. Blog post, Animal Endocrine Clinic, September 2, 2012.
2. Felimazole-Coated Tablets. Product insert. Available at: www.dechra-us.com/files/dechraUSA/downloads/Product%20inserts/Felimazole.pdf 
3. Padula C, Pappani A, Santi P. In vitro permeation of levothyroxine across the skin. Int J Pharm 2008 12;349:161-165. 
4. Padula C, Nicoli S, Santi P. Innovative formulations for the delivery of levothyroxine to the skin. Int J Pharm 2009;372:12-16.
5. Peterson ME. Alternative Dosage Forms of L-Thyroxine for Hypothyroid Dogs. Blog post, Insights into Veterinary Endocrinology, March 28, 2012.

Diagnosing Naturally Occurring Hypothyroidism in Cats

I have a 5-year-old female DSH cat that has recently been diagnosed with hypothyroidism.  This diagnosis was based on a low serum T4 value that was detected during a pre-anesthetic workup for a preventative dental procedure. She had been looking unthrifty and "off" to me at home for a while, but has had no other signs of illness. Her appetite remains normal with no signs of vomiting or diarrhea.

We sent out a complete serum thyroid panel two weeks after the initial low T4 value and the results were as follows:

• Total T4: 0.3 µg/dL (reference range, 0.8-4.7 µg/dL)
• Free T4 - 0.35 ng/dL (reference range, 0.7-2.6 ng/dL)
• Total T3: <35 ng/dL (52-182 ng/dL)
• TSH 0.01 ng/ml (reference range, 0.05-0.42 ng/ml)

How would you interpret this panel?  Should we treat her as being hypothyroid? She has never been hyperthyroid and has never been treated with methimazole or radioiodine.

Is there value in trying to use one of the herbal remedies  for thyroid support (e.g., Thytrophin PMG) or should we just start her on thyroid hormone? If you think we should use thyroid hormone, which product is best to use (L-T4, L-T3, or a combination)?

My Response:

Based on your cat's serum thyroid panel, the results are not supportive of primary hypothyroidism. As the thyroid gland fails in hypothyroidism, the pituitary would respond by increasing the secretion of thyroid stimulating hormone (TSH) (1-4). In your cat, all of the serum thyroid hormone values (T4, T3, and free T4) are very low. However, the serum TSH level remains well within the reference range limits, not high as would be expected with primary hypothyroidism.

Again, the result of this thyroid panel goes against a diagnosis of primary hypothyroidism. Spontaneous hypothyroidism (i.e., not secondary to treatment of hyperthyroidism) is extremely rare in the adult cat, with only a few cases reported (4,5), so I'm not surprised that the serum TSH value is normal in your cat.

The most likely explanation for these serum thyroid results is that your cat is likely suffering from another illness. It's well known that any nonthyroidal disease can act to lower circulating T4 and T3 concentrations in cats (6-10); thyroid hormone replacement in those cats would unlikely be of any benefit.

I'm assuming that you did routine blood work (CBC, serum chemistry panel, urinalysis) in addition to the T4 for the pre-dental panel. Were there any abnormalities on this blood-work or urine?  If not, a chest radiography or abdominal ultrasound may be indicated as the next step to search for the underlying problem. Once we determine what's wrong with your cat and treat the primary problem, the serum thyroid values will likely normalize.

In any case, supplementation with thyroid hormone or any one of the herbal remedies are unlikely to be of any use and have the potential to do harm (11,12), depending on the underlying cause of your cats problems.  If your cat was indeed hypothyroid (which she isn't!), we generally use twice daily L-T4 replacement, but some cats do appear to respond better to combination L-T4/L-T3 therapy.

References:

1. Baral R, Peterson ME. Thyroid gland disorders In: Little SE, ed. The Cat: Clinical Medicine and Management. Philadelphia: Elsevier Saunders, 2012;571-592.
2. Peterson ME. Feline focus: Diagnostic testing for feline thyroid disease: Hypothyroidism. Compend Contin Educ Vet 2013;35:E1-E6. 
3. Greco DS. Diagnosis of congenital and adult-onset hypothyroidism in cats. Clin Tech Small Anim Pract 2006;21:40-44. 
4. Daminet S. Feline hypothyroidism In: Mooney CT, Peterson ME, eds. Manual of Canine and Feline Endocrinology Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;1-5.
5. Rand JS, Levine J, Best SJ, et al. Spontaneous adult-onset hypothyroidism in a cat. J Vet Intern Med 1993;7:272-276. 
6. Peterson ME, Melian C, Nichols R. Measurement of serum concentrations of free thyroxine, total thyroxine, and total triiodothyronine in cats with hyperthyroidism and cats with nonthyroidal disease. J Am Vet Med Assoc 2001;218:529-536. 
7. Peterson ME, Gamble DA. Effect of nonthyroidal illness on serum thyroxine concentrations in cats: 494 cases (1988). J Am Vet Med Assoc 1990;197:1203-1208. 
8. Mooney CT, Little CJ, Macrae AW. Effect of illness not associated with the thyroid gland on serum total and free thyroxine concentrations in cats. J Am Vet Med Assoc 1996;208:2004-2008. 
9. McLoughlin MA, DiBartola SP, Birchard SJ, et al. Influence of systemic nonthyroidal illness on serum concentrations of thyroxine in hyperthyroid cats. J Am Anim Hosp Assoc 1993;29:227-234. 
10. Mooney CT. The effects of nonthyroidal factors on tests of thyroid function. Australian College of Veterinary Scientists, Science Week 2010;28-30.  
11. Bello G, Paliani G, Annetta MG, et al. Treating nonthyroidal illness syndrome in the critically ill patient: still a matter of controversy.  Curr Drug Targets 2009;10:778-787. 
12. Adler SM, Wartofsky L. The nonthyroidal illness syndrome. Endocrinol Metab Clin North Am 2007;36:657-672, vi.

Transient Hypothyroidism in Cats Following Radioiodine

Transient hypothyroidism, with the development of subnormal thyroid hormone levels, is common after radioiodine therapy. However, such suppression in the circulating thyroid hormone concentrations is usually mild and generally does not require thyroid hormone replacement therapy.

Why Transient Hypothyroidism Develops after I-131 Treatment

Prior to treatment of a hyperthyroid cat, the high circulating levels of the thyroid hormones (T3 and T4) have a negative feedback effect on the pituitary gland to suppress thyroid stimulating hormone (TSH) release (1-4). Therefore, serum TSH concentrations in hyperthyroid cats fall to low or undetectable levels (Figure 1).

Fig. 1: In normal cat, normal levels of thyroid hormone (T4 and T3) are controlled by TSH, a hormone secreted by the pituitary gland. In hyperthyroid cats, their thyroid tumor(s) secrete too much T4 and T3, resulting in a decrease in pituitary TSH secretion. Without adequate amounts of circulating TSH, any remaining normal thyroid tissue stops working and will atrophy.

Since adequate amounts of circulating TSH are needed by normal thyroid tissue for both iodine uptake and thyroid hormone secretion, the decreased circulating TSH concentrations that accompany persistent hyperthyroidism lead to atrophy of the normal (nonadenomatous) thyroid tissue (Figures 1 & 2). In contrast, because the adenomatous thyroid nodules (thyroid tumors) are autonomous and do not require circulating TSH for iodine uptake or thyroid hormone secretion, these thyroid tumors continue to exhibit both growth and hyperfunction (Figure 2).

See the thyroid scans below (Figure 2), which illustrate how cats with a thyroid adenoma affecting only 1 of the 2 thyroid lobes will show complete suppression of the normal lobe and not take up any radioactivity (labeled Unilateral, left panel). In contrast, the cats in the middle and right panels have both thyroid lobes involved with tumor (5).

Fig. 2: Thyroid scans in 3 hyperthyroid cats. All had low serum TSH concentrations. In the cat with a unilateral thyroid adenoma (left panel), the normal thyroid lobe is not visible — it has stopped functioning properly and has atrophied as a result of the low circulating TSH concentrations.

Many cats treated with radioiodine go through a period of transient, mild hypothyroidism after the 131-I treatment has destroyed their thyroid tumor(s). When rechecked within the first month after radioiodine therapy, many hyperthyroid cats have low to low-normal serum T4 concentrations (Figure 3).

If not overdosed with radioiodine, almost all these cats have some remaining “normal” thyroid tissue surrounding the thyroid tumor tissue, which has been chronically suppressed by the hyperthyroid state. However, now that the hyperthyroidism has been cured, pituitary TSH secretion eventually recovers and serum TSH concentrations will rise, resulting in stimulation of any remaining normal, but previously dormant, thyroid tissue.

Fig. 3: In hyperthyroidism,  the high T4 and T3 levels suppress pituitary TSH secretion to very low levels. Once the thyroid tumor is irradiated and destroyed, the T4 and T3 levels will fall to normal or even low levels for 1-2 months. With time, however, the pituitary gland recovers and starts to secrete TSH once again (sometimes to higher-than-normal amounts for a time). This allows any remaining normal thyroid tissue to become active once again and secrete normal amounts of thyroid hormone.

Most cats with a sufficient volume of normal thyroid tissue regain the ability to produce adequate amounts of thyroid hormone to maintain euthyroidism within 3 months of radioiodine therapy. Rarely, cats require as long as 6 months of chronically increased endogenous TSH levels to recover lost thyroid function and regain the ability to maintain normal thyroid hormone levels.

Bottom Line
Since transient hypothyroidism is common and and most cats will recover normal thyroid function with time, L-T4 replacement is not generally indicated at the time of this early recheck period.

However, if evidence of new or worsening kidney disease is found, short-term or permanent L-T4 replacement may be indicated to help preserve any residual renal function and prevent irreversible renal injury. I'll be discussing more about hypothyroidism and kidney function in a upcoming post.

References:

1. Baral R, Peterson ME. Thyroid gland disorders In: Little SE, ed. The Cat: Clinical Medicine and Management. Philadelphia: Elsevier Saunders, 2012;571-592.
2. Mooney CT, Peterson ME. Feline hyperthyroidism In: Mooney CT, Peterson ME, eds. Manual of Canine and Feline Endocrinology Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;199-203.
3. 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.
4. Peterson ME, Broome MR. Radioiodine for feline hyperthyroidism In: Bonagura JD,Twedt DC, eds. Kirk's Current Veterinary Therapy, Volume XV. Philadelphia: Saunders Elsevier, 2013;in press.
5. Broome MR. Thyroid scintigraphy in hyperthyroidism. Clin Tech Small Anim Pract 2006;21:10-16. 

January is National Thyroid Awareness Month

"If your thyroid isn't working properly, neither are you."

January is Thyroid Awareness Month, which is sponsored by the American Association of Clinical Endocrinologists (AACE).  We must remember that thyroid disease commonly affects people, as well as our cats and dogs. The AACE also estimates that approximately 30 million Americans may be affected by thyroid disorders (hypothyroidism, hyperthyroidism, and thyroid cancer) — with half of these cases currently undiagnosed.

In humans, the thyroid gland is a small, butterfly-shaped gland found immediately below the Adam’s apple. This gland produces hormones that influence every organ, tissue and cell in your body. If thyroid disease is left untreated, there are serious consequences including elevated cholesterol levels, heart disease, infertility, muscle weakness, and osteoporosis.

Testing for thyroid disease is easy, although not routinely included in an annual physical blood work. However, the diagnosis of thyroid disease can sometimes be challenging. Patients often present with vague, general clinical manifestations that may not be obvious to either the doctor or patient. Understanding the facts about thyroid disease and its symptoms is the best defense in diagnosing and treating thyroid disease.

What Are The Symptoms Of Thyroid Disease In Humans?

The following are some of the symptoms of various thyroid conditions and diseases.

Hypothyroidism
The symptoms of hypothyroidism (i.e., an underactive thyroid) tend to mirror the slowing down of physical processes that result from insufficient thyroid hormone. Common symptoms include fatigue, weight gain, constipation, fuzzy thinking, low blood pressure, fluid retention, depression, body pain, slow reflexes, and much more.

Hyperthyroidism
The symptoms of hyperthyroidism (i.e., an overactive thyroid) tend to reflect the rapid metabolism that results from an oversupply of thyroid hormone. Common symptoms include anxiety, insomnia, rapid weight loss, diarrhea, high heart rate, high blood pressure, eye sensitivity or bulging, and vision disturbances.

Thyroid Nodules or Goiter
Symptoms of goiter — an enlarged thyroid gland— include a swollen, tender or tight feeling in the neck or throat, hoarseness or coughing, and difficulty swallowing or breathing. Sometimes, the goiter is visible to yourself or others.

Some thyroid nodules cause no symptoms, while others may cause difficulty swallowing, a feeling of fullness, pain or pressure in the neck, a hoarse voice, or neck tenderness. Some nodules trigger hyperthyroid-like symptoms such as palpitations, insomnia, weight loss, anxiety, and tremors. Nodules can also trigger hypothyroidism, and symptoms might include weight gain, fatigue, and depression.

Thyroid Cancer
Although many patients are asymptomatic at first, possible symptoms of thyroid cancer include a lump in the neck, voice changes, difficulty breathing or swallowing, or lymph node swelling.

Thyroiditis
Symptoms of thyroiditis typically include pain and tenderness in the thyroid area, neck and throat, difficulty sleeping. Thyroiditis may also trigger traditional hypothyroid or hyperthyroid symptoms. 

Where To Get More Information?

For more information on thyroid disease and/or to find a medical expert in thyroid conditions, please visit the American Association of Clinical Endocrinologists website. The AACE’s Thyroid Awareness website also features articles, videos and FAQ on thyroid conditions.

For a detailed description of various thyroid disorders in human patients, including hypothyroidism and Hashimoto’s thyroiditis, hyperthyroidism and Graves’ disease, multinodular goiter, thyroid nodules and thyroid cancer, I'd strongly recommend that you visit the Thyroid Disease Manager Website.

Thyroid Disease Manager offers an up-to-date analysis of all aspects of human thyroid disease and thyroid physiology. It provides physicians, researchers, and patients from around the world with an authoritative, current, complete, objective, free, and down-loadable source on the thyroid and its diseases.

Useful Links:

• American Association of Clinical Endocrinologists (AACE) website — https://www.aace.com/
• AACE's Thyroid Awareness website — www.thyroidawareness.com
• Thyroid Disease Manager website —www.thyroidmanager.org

Complications of Thyroidectomy in Cats: Postoperative Hypothyroidism

Iatrogenic hypothyroidism in a cat. Note the matted hair coat.

Most hyperthyroid cats are readily cured quite easily with the use of surgical thyroidectomy (1-6). Most cats that are cured with surgery, however, will develop iatrogenic hypothyroidism, which may be temporary or permanent depending on the extent of surgery (i.e, unilateral vs. bilateral thyroidectomy).

After successful surgical thyroidectomy in a cat with hyperthyroidism, the serum thyroid hormone concentrations (both T4 and T3) should fall to low-normal or low concentrations by 24 hours postoperatively (8-10). I recommend checking a serum T4 concentration before the cat is discharged from the hospital (within 1-2 days of surgery) to ensure that the procedure has been successful in removing all adenomatous thyroid tissue.

If the serum T4 concentration remains high or has only fallen into the high-normal range, it is very likely that remaining adenomatous tissue remains and that the cat will require additional treatment (I'll be covering persistent hyperthyroidism in my next post). If, on the other hand, the serum T4 value is subnormal, treatment for hypothyroidism must be considered.

Hypothyroidism After Unilateral Thyroidectomy

In cats that have unilateral thyroid disease, only one thyroid lobe is generally removed (i.e., unilateral thyroidectomy is performed). Because the remaining "normal" thyroid lobe in these cats has been suppressed and is not functioning normally, serum thyroid hormone concentrations are expected to fall to subnormal levels for 1 to 2 months. This transient hypothyroid state is followed by a return to euthyroidism by 3 months postoperatively, as the remaining thyroid lobe recovers and starts to function once again (8).

After treatment of a hyperthyroid cat with unilateral thyroidectomy, thyroid hormone supplementation is not generally recommended during this period of transient hypothyroidism.  The main reason for this recommendation is that thyroid hormone replacement will postpone —and may even prevent— full recovery of normal thyroid function.

The major exception to this rule pertains to cats that have or develop concurrent kidney disease. It is now clear that hypothyroidism (even transient or temporary) can lower renal blood flow and the glomerular filtration rate (GFR), which can lead to worsening of concurrent chronic renal disease (11-14). Treating the hypothyroidism can raise the renal blood flow and GFR to an acceptable level, thus helping to protect kidney function in these cats (15-17).

Hypothyroidism After Bilateral Thyroidectomy

Almost all cats that undergo bilateral or "total" thyroidectomy will become hypothyroid and will benefit from thyroid hormone replacement therapy. Remember that after one performs a total thyroidectomy and removes both adenomatous thyroid lobes, we expect to find undetectable thyroid hormone values. If the serum T4 concentration remains high or only falls to the reference range limits, it is very likely that remaining adenomatous tissue remains and that the cat will require additional treatment (7).

Initial thyroid hormone replacement dose
After bilateral thyroidectomy has been performed, L-thyroxine or L-T4 (0.1 mg, once or twice daily) should be started as soon as we document that the postoperative serum T4 concentration is low to undetectable (8-10). While the use of divided dosing will result in less fluctuation of the circulating T4 concentrations compared to administration of the same total dose as a single daily bolus, the biological action of thyroid hormones (within the tissues and cells) far exceeds that of their serum half-life. This explains why many cats will do well on once-daily L-T4 supplementation.

Either L-T4 pills (e.g, Soloxine, Virbac; Thyro-Tabs, Vetamix) or liquid suspension (e.g., Leventa solution, Merke Animal Health) can be used successfully in cats. When thyroid hormone supplementation is given to cats, the dose should be given at the same time(s) each day.

The supplement can be given either with food or on an empty stomach, but one should be consistent in how it is dosed to avoid marked fluctuations in the absorption of L-T4. Absorption of the L-T4  is likely better when administered on an empty stomach, as has been reported in both humans and dogs (18,19). However, studies comparing absorption of L-T4 in the fed vs. fasting state have not yet been reported in cats.  Nevertheless, we can expect that a higher daily dose of L-T4 might be needed if the thyroid hormone supplement is given at the time of feeding (e.g., if the medication is placed in the food).

Monitoring L-T4 supplementation
The ideal replacement dosage is based on the results of a serum thyroid panel, which includes at minimum the determination of serum T4 and TSH concentrations (20-22). This serum thyroid panel is collected 4 hours after the cat's morning dose of L-T4 is administered (23). If serum T4 is low to low-normal and serum TSH concentration is high, the dose of L-T4 should be increased or given twice daily, or both.  If the serum T4 is high-normal to high, especially if the cat is showing signs of hyperthyroidism (i.e., weight loss despite a good appetite), the dose of L-T4 should be reduced.

Once the proper daily replacement dose is determined for the individual cat, the T4 supplementation can be safely continued indefinitely. However, in some cats, the low serum concentrations of T4 and T3 may spontaneously increase into the normal reference range after a few weeks to months (6,8,24,25). Small pieces of adenomatous thyroid tissue left attached to the thyroid capsule (in the area of the parathyroid gland) can regrow enough to secrete normal amounts of thyroid hormone. Thyroid hormone administration can then be discontinued.

To evaluate whether or not L-T4 replacement therapy can be discontinued, we must stop the thyroid supplement for at least 2 days and repeat a serum thyroid hormone panel. If normal values are maintained after being off L-T4 for 48 hours, the thyroid hormone supplementation can  be discontinued.

Monitoring Cats After Thyroidectomy

In all hyperthyroid cats treated with thyroidectomy, thyroid function testing should be monitored  at 6- to 12-month intervals for the rest of the cat's life. In some cats, relapse of hyperthyroidism can develop, especially after many months. Such hyperthyroid cats can be difficult to manage, especially is reoperation is contemplated.

In my next post, I'll be covering both persistent and recurrent hyperthyroidism and how to diagnose and treat these difficult cases.

References:

1. 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.
2. Baral RM, Peterson ME. Thyroid gland disorders In: Little SE, ed. The Cat: Clinical Medicine and Management. St. Louis: Elsevier Saunders, 2012;571-592.
3. Panciera DL, Peterson ME, Birchard, SJ: Diseases of the thyroid gland. In: Birchard SJ, Sherding RG (eds): Manual of Small Animal Practice (Third Edition), Philadelphia, Saunders Elsevier, pp 327-342, 2006.
4. Flanders JA. Surgical therapy of the thyroid. Veterinary Clinics of North America. Small Animal Practice 1994;24:607–621. 
5. Padgett S. Feline thyroid surgery. Veterinary Clinics of North America. Small Animal Practice 2002;32:851–859. 
6. Birchard, SJ. Thyroidectomy in the cat. Clinical Techniques in Small Animal Practice 2006;21:29-33. 
7. Peterson ME. Treatment of severe, unresponsive, or recurrent hyperthyroidism in cats. Proceedings of the 2011 American College of Veterinary Internal Medicine (ACVIM) Forum. 2011; 104-106. 
8. Peterson ME, Randolph JF, Mooney CT: Endocrine diseases, In: Sherding RG (ed): The Cat: Diagnosis and Clinical Management. (2nd Ed) New York, Churchill Livingstone, 1994; 1404-1506.
9. Peterson ME: Feline hypothyroidism, In: Kirk RW (ed): Current Veterinary Therapy X. Philadelphia, WB Saunders Co., pp 1000-1001, 1989.
10. Daminet S. Feline hypothyroidism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Small Animal Endocrinology. 4th ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012:111-115.
11. Langston CE, Reine NJ. Hyperthyroidism and the kidney. Clin Tech Small Anim Pract 2006;21:17-21.
12. Syme HM. Cardiovascular and renal manifestations of hyperthyroidism. Vet Clin North Am 2007; 37:723-743.
13. van Hoek I, Lefebvre HP, Peremans K, et al. Short- and long-term follow-up of glomerular and tubular renal markers of kidney function in hyperthyroid cats after treatment with radioiodine. Domest Anim Endocrinol 2009;36:45-56.
14. Williams TL, Elliott J, Syme HM. Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism. J Vet Intern Med 2010;24:1086-1092.
15. Gommeren K, van Hoek I, Lefebvre HP, et al. Effect of thyroxine supplementation on glomerular filtration rate in hypothyroid dogs. J Vet Intern Med 2009;23:844-849.
16. Panciera DL, Lefebvre HP. Effect of experimental hypothyroidism on glomerular filtration rate and plasma creatinine concentrations in dogs.  J Vet Intern Med 2009;23:1045-1050.
17. Broome MR. Feline hyperthyroidism - avoiding further renal injury. Proceedings of the Southern California Veterinary Medical Association, 2012.
18. Wenzel KW, Kirschsieper HE. Aspects of the absorption of oral L-thyroxine in normal man. Metabolism 1977;26:1-8.  
19. Le Traon G, Burgaud S, Horspool LJ. Pharmacokinetics of total thyroxine in dogs after administration of an oral solution of levothyroxine sodium. J Vet Pharmacol Ther 2008;31:95-101. 
20. Wakeling J, Moore K, Elliott J, et al. Diagnosis of hyperthyroidism in cats with mild chronic kidney disease. J Small Anim Prac 2008;49:287-294.
21. Wakeling J. Use of thyroid stimulating hormone (TSH) in cats. Can Vet J 2010;51:33-34.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797347/
22. Peterson ME. Diagnostic testing for thyroid disease in cats: Hypothyroidism. Comp Cont Educ Pract 2012; in press.
23. Le Traon G, Burgaud S, Horspool L. Pharmacokinetics of L-thyroxine after oral administration to healthy cats. Proceedings of the 19th ECVIM-CA Congress (European College of  Veterinary Internal Medicine - Companion Animals). 2009;209.
24. 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. 
25. Swalec KM, Birchard SJ. Recurrence of hyperthyroidism after thyroidectomy in cats. J Am Anim Hosp Assoc 1990;26:433-437. 

How Many Ways Can the Thyroid Malfunction?

Thyroid disease (i.e., hypothyroidism, hyperthyroidism, and thyroid tumors) is common in dogs and cats. Dr. Ann Hohenhaus, an oncologist and former colleague of mine at the Animal Medical Center in New York City, wrote the following blog post on WebMD about 2 dogs and a cat with thyroid disease that I thought was worth sharing.

The first case concerns a dog with thyroid cancer; the second case a hyperthyroid cat who previously had intestinal lymphoma (a cancer); and the third case of a dog with hypothyroidism.

How Many Ways Can the Thyroid Malfunction?
By Ann Hohenhaus, DVM

The thyroid gland sits in the neck of dogs and cats, just below the voice box, and controls metabolic functions. Most of the time, a routine physical examination cannot detect the organ if it is normal.

Last week, my patient list ran the gamut of thyroid dysfunction. Here is a sampling:

A Tail of Two Thyroids
Some days, strange coincidences happen in the waiting room. Today it was two dogs, both with thyroid cancer. Although measuring 15 centimeters in length, Beckey’s thyroid tumor had been surgically removed. The biopsy showed her tumor trying to escape into the lymph vessels and she was waiting her turn for chemotherapy, administered to halt the spread. Her treatment involves intravenous administration of two different chemotherapy agents and Beckey so far has sailed through the treatment with flying colors.

As Beckey was leaving the waiting room, Henry entered. A CT scan showed his thyroid tumor had already spread to the lymph nodes in his neck, precluding surgical removal. He was in for a check-up following completion of four radiation therapy treatments. Careful measurement of his tumor with calipers showed no increase in tumor size. The radiation treatment arrested tumor growth but had given him a sore esophagus. I had warned the owners about this type of side effect before we started treatment and told them to expect it to start resolving about two weeks after he completed his treatment. Henry did not disappoint us. Through telephone triage, we had already rearranged his medications to make his throat less painful. Henry spends summer in the country but in the fall he will come back to The AMC for measurement of the tumor and a chest x-ray.

Old Patient, New Problem
Otra’s family was worried. This cute kitty had completed chemotherapy for intestinal lymphoma about a year ago, but suddenly her weight plummeted. I could see from the look on their faces they were sure the cancer was back. Auscultation of Otra’s heart discovered a very elevated heart rate, prompting a test of her thyroid levels. Overactive thyroid glands ramp up the cat’s metabolism and they lose weight despite eating well, have a high heart rate, and are very peppy. An abdominal ultrasound showed no evidence the lymphoma had recurred and blood tests showed the thyroid was overactive. I sent thyroid-suppressing medications home with the relieved family and planned to reassess the thyroid hormone levels in two weeks.

Porterhouse to Pork Chop
Every time I saw Mango to follow up on a skin tumor that had been completely removed via surgery, she had gained another pound. This 60-pound Portuguese Water Dog should have weighed 50 pounds. The owners took her swimming, fed her diet food from feeding toys, and still she gained two more pounds. During an evaluation for a urinary tract infection, we noted her thyroid hormone levels were borderline low. When we retested the levels three months later, we confirmed diagnosis of hypothyroidism. Low thyroid function, the opposite of Otra’s problem, can cause weight gain. Since she started treatment with thyroid supplementation, Mango has lost nearly 6 pounds and gone from a 20-ounce porterhouse to a 4-ounce pork chop over the past few months!

There you have it, thyroid malfunction runs the gamut of disease: overactive, underactive, and two different tumors, all in one tiny organ.

My Related Posts:

• Hypothyroidism: One of the Top 10 Diagnosed Diseases of Dogs 
• How is Canine Hypothyroidism Diagnosed? 
• How Do We Confirm a Diagnosis of Hypothyroidism in Dogs? 
• How Do We Treat Dogs With Hypothyroidism? 
• Hyperthyroid in Cats: Table of Contents 
• Treatment Options and Considerations for Hyperthyroid Cats 
• More Hyperthyroid Posts, etc 

Thyroid Tumors and Hyperthyroidism in Dogs

Large neck mass in a dog with
thyroid cancer (carcinoma)

In dogs, thyroid tumors are common, representing approximately 1 to 4% of all canine neoplasms. Most thyroid tumors in the dog are non-functional and do not lead to hyperthyroidism — completely different from the situation in cats, where most cats with thyroid tumors are hyperthyroid (for more information, see links to my related posts, below). 

As opposed to the relatively small, non-invasive and benign thyroid tumors associated with hyperthyroidism in cats, most clinically detected thyroid tumors in dogs are large, invasive tumors associated with thyroid cancer (carcinomas).

Nature of Thyroid Cancer in Dogs
In dogs with thyroid carcinoma, both local invasion of tumor into adjacent structures (e.g., esophagus, trachea, cervical musculature, nerves, or thyroid vessels) and distant metastasis (e.g., lung, liver, or regional lymph nodes) are common.

Approximately 50% of dogs with thyroid carcinoma have documented metastasis at time of diagnosis. During the natural course of disease, 65% to 90% of dogs with untreated disease will develop metastasis to a wide variety of tissue.

Thyroid Tumors and Hyper- and Hypothyroidism
In most dogs with thyroid tumors, their thyroid function remains normal. Up to a third of dogs with thyroid cancer will develop hypothyroidism from destruction of normal thyroid tissue.

Only 10% of thyroid carcinomas in dogs are overactive, producing clinical signs of hyperthyroidism. Although thyroid adenomas producing hyperthyroidism have been described, the incidence of benign thyroid tumors causing hyperthyroidism in dogs is very low. In dogs, a thyroid tumor causing hyperthyroidism should always be presumed to be a carcinoma until proven otherwise. Again, this is in stark contrast to the situation in hyperthyroid cats, in which thyroid carcinoma is rare (less than 5% of in cats).

Clinical Features 
Most dogs with thyroid tumors are of middle- to old-age (greater than 5 years; average age, 10 years). There is no sex predilection. Breeds reported to be at increased risk of developing thyroid tumors include boxers, beagles, Golden Retrievers, and Labrador Retrievers.

Many dogs with thyroid tumors are presented because the owner has noticed an enlargement of the neck. In more than 75% of dogs diagnosed in one survey, either the cervical swelling was the only reason for seeking veterinary care or the thyroid mass was detected by the veterinarian during an examination for another problem.

Because of the large tumor volume and high incidence of both local invasion and distant metastasis, clinical signs such as trouble breathing (dyspnea), cough, hoarseness, alternation in bark, vomiting, poor appetite, and weight loss may be reported, especially in dogs with nonfunctional thyroid tumors. A surprising number of owners, however, fail to report any clinical signs in their dogs.

Of all thyroid tumors in dogs, approximately 10% will become hyperthyroid, and in these dogs, the hyperthyroid state is usually the major reason for examination. Increased thirst and urination are usually the earliest and most predominant signs associated with hyperthyroidism in dogs. Weight loss, despite an increase in appetite, is also common.

Diagnosis
Thyroid imaging or scanning (thyroid scintigraphy) is useful in the evaluation of dogs with thyroid tumors because the procedure can help locate where the thyroid tissue is located (both normal tissue, as well as benign and malignant tumors).  Thyroid imaging can also be performed to help determine the extent of thyroid invasion or metastasis.  

Definitive diagnosis of thyroid carcinoma is best made by either incisional biopsy or surgical excision of the thyroid mass, followed by histological examination of the thyroid tissue. Despite the fact that most thyroid tumors detected in clinical practice are easily palpable, they are not simple to biopsy. Because of the vascular and invasive nature of canine thyroid carcinomas, hemorrhage is a common complication.

Treatment
Treatment of thyroid neoplasia in dogs is dictated by the size of the primary tumor, extent of local tissue invasion, presence of detectable metastasis, presence of hyper- or hypothyroidism, and available treatment options.

Because most clinically detected thyroid tumors in the dog are malignant, treatment is rarely curative. Nevertheless, one should generally advise some form of treatment because palliative relief and increased lifespan can usually be achieved in most dogs with thyroid carcinoma.

Surgical removal of a small thyroid tumor in a dog

Surgery, chemotherapy, cobalt irradiation, and use of radioactive iodine therapy, alone or in combination, may be indicated depending on the individual dog. Medical control of the hyperthyroid state can be achieved by the daily administration of an antithyroid drug such as methimazole or carbimazole (5 to 15 mg/dog, twice, daily), but such medical treatment will not do anything to prevent tumor growth or metastasis.

Suggested Reading:

1. Panciera DL, Peterson ME, Birchard, SJ: Diseases of the thyroid gland. In: Birchard SJ, Sherding RG (eds): Manual of Small Animal Practice (Third Edition), Philadelphia, Saunders Elsevier, 2006;327-342.
2. Peterson ME: Hyperthyroidism and thyroid tumor in dogs. In: Melian C, Perez Alenza MD, Peterson ME, Diaz M, Kooistra H (eds): Manual de Endocrinología en Pequeños Animales (Manual of Small Animal Endocrinology). Multimedica, Barcelona, Spain, 2008;113-125.
3. Mooney CT. Canine hyperthyroidism In: Mooney CT,Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;86-91.

My Related Posts on Thyroid Disease in Dogs and Cats:

• Hypothyroidism: One of the Top 10 Diagnosed Diseases of Dogs 
• How is Canine Hypothyroidism Diagnosed? 
• How Do We Confirm a Diagnosis of Hypothyroidism in Dogs? 
• How Do We Treat Dogs With Hypothyroidism? 
• Hyperthyroid in Cats: Table of Contents 
• Treatment Options and Considerations for Hyperthyroid Cats 
• More Hyperthyroid Posts, etc 

World Thyroid Day is May 25, 2012

On May 25th, 2012, we recognize the 5th Annual World Thyroid Day.  Established in 2008, World Thyroid Day highlights five major goals to:

• Increase awareness of thyroid health,
• Promote understanding of advances made in treating thyroid diseases,
• Emphasize the prevalence of thyroid diseases,
• Focus on the urgent need for education and prevention programs, and
• Expand awareness of new treatment modalities.

In humans, dogs and cats, the thyroid, a large endocrine gland located in the neck, produces hormones that influence virtually every cell, tissue and organ in the body. The thyroid gland regulates the body's metabolism — the rate at which the body produces energy from nutrients and oxygen — and affects critical body functions, such as energy level and heart rate.

Diseases of the thyroid  gland include hyperthyroidism, hypothyroidism, and thyroid cancer.  These disorders are very common and affect tens of millions of people worldwide. As we all know from reading this blog, the same thyroid diseases are also common in dogs and cats.

For more information, see: www.worldthyroidday.com.

Stem Cell Therapy for Thyroid Disease in Cats and Dogs

Questions:
Stem cell therapy is coming into the limelight for animals and humans. I've read of its success treating diabetes, so wonder about the thyroid as well.

Do you have any knowledge of this, or can you point me in a direction to explore? Can stem cell transplantation help cure my older cat with hyperthyroidism? He hates taking the daily methimazole!

My Response:
Stem cells are biological cells found in all multicellular organisms (including humans, dogs, and cats). They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. Stem cells may one day be used to make cells and tissues for therapy of many diseases, including Parkinson's disease, Alzheimer's disease, spinal cord injury, heart disease, diabetes and arthritis (1).

Stem Cells (Picture from: http://biologyblog.edublogs.org/)

Diabetes mellitus is the main endocrine disorder in which research in stem cell therapy has been investigated (2). In many human patients, as in our canine and feline diabetics, diabetes mellitus will frequently reach the stage of life threatening and severely disabling complications, which cannot be controlled by insulin alone.

Several other hormone deficiency disorders (hypothyroidism, Addison's disease) could potentially be helped by stem cell transplantation However, it is relatively easy to provide hormone replacement for these disorders, so there is not a huge incentive to use stem cell therapy for these diseases.

There is ongoing research concerning stem cell therapy for thyroid disease in people (3-6), but I do not know of anyone working on stem cell therapy for thyroid disease in cats. However, notice that — even in people — they are concentrating on stem cell therapy for thyroid cancer (4,6).  Again, it's relatively cheap and easy to provide thyroid supplements for hypothyroidism. Hyperthyroidism is relatively easy to cure with radioiodine (7-10), so investigators aren't overly concerned with stem cell transplantation for that condition.

References:

1. Sharma S, Vyas G, Gawarikar SB, et al. Stem cell transplantation: brief review and current status. Journal of the Indian Medical Association 2011;109:570-574, 579-581. 
2. Fiorina P, Voltarelli J, Zavazava N. Immunological applications of stem cells in type 1 diabetes. Endocrine Reviews 2011;32:725-754.
3. Lin RY. New insights into thyroid stem cells. Thyroid 2007;17:1019-1023.
4. Thomas D, Friedman S, Lin RY. Thyroid stem cells: lessons from normal development and thyroid cancer. Endocrine-Related Cancer 2008;15:51-58. 
5. Davies TF, Latif R, Minsky NC, et al. Clinical review: The emerging cell biology of thyroid stem cells. The Journal of Clinical Endocrinology and Metabolism 2011;96:2692-2702.
6. Lin RY. Thyroid cancer stem cells. Nature Reviews: Endocrinology 2011;7:609-616.
7. Radioiodine therapy for hyperthyroidism. Drug and Therapeutics Bulletin 2006;44:44-48. 
8. Franklyn JA, Boelaert K. Thyrotoxicosis. Lancet 2012;379:1155-1166.
9. Peterson ME: Radioiodine treatment for hyperthyroidism. Clinical Techniques in Small Animal Practice 2006;21:34-39.
10. Peterson ME, Broome MR: Radioiodine for hyperthyroidism. In: Bonagura JD, Twedt DC (eds): Current Veterinary Therapy XV. Philadelphia, Saunders Elsevier, 2012, in press.

Top 10 Cat and Dog Medical Conditions of 2011

Nation's Largest Pet Insurer Reveals Most Common Causes of Veterinary Visits

Veterinary Pet Insurance Co. (VPI), the nation's oldest and largest provider of pet health insurance, recently sorted its database of more than 485,000 insured pets to determine the top 10 dog and cat medical conditions in 2011. Click here to see the original report from VPI or see the lists below.

For cats, notice that two endocrine problems, hyperthyroidism and diabetes, were among the top 5 most common feline diseases. For dogs, the only endocrine problem that made the top 10 list was hypothyroidism, but I suspect that hyperadrenocorticism Cushing's syndreome) and diabetes were not far behind.

Top 10 pet medical conditions, according to Veterinary Pet Insurance's database of more than 485,000 insured pets:

Cats

Palpating the thyroid tumor
in a hyperthyroid cat

1. Lower urinary tract disease 
2. Gastritis 
3. Chronic renal failure 
4. Hyperthyroidism 
5. Diabetes mellitus
6. Enteritis/diarrhea 
7. Skin allergy 
8. Periodontitis/dental disease 
9. Ear infection 
10. Upper respiratory infection 

 Dogs

Truncal hair loss
in a hypothyroid Doberman

1. Ear infection 
2. Skin allergy 
3. Skin infection/hot spots 
4. Gastritis/vomiting 
5. Enteritis/diarrhea 
6. Arthritis 
7. Bladder infection 
8. Soft tissue trauma 
9. Non-cancerous tumor 
10. Hypothyroidism

Pet Obesity Epidemic Expanding, But Owners in Denial

Big Pets Get Bigger: 

Latest Survey Shows US Dog and Cat Obesity Epidemic Expanding 

The “fat pet gap” continues to widen according to the latest nationwide survey conducted by the Association for Pet Obesity Prevention (APOP). The fifth annual veterinary survey found 53 percent of adult dogs and 55 percent of cats to be classified as overweight or obese by their veterinarian. That equals 88.4 million pets that are too heavy according to veterinarians.

“The most distressing finding in this year’s study was the fact that more pet owners are unaware their pet is overweight.” comments APOP founder Dr. Ernie Ward. “22 percent of dog owners and 15 percent of cat owners characterized their pet as normal weight when it was actually overweight or obese. This is what I refer to as the “fat pet gap” or the normalization of obesity by pet parents. In simplest terms, we’ve made fat pets the new normal.”

 Perhaps even worse was the finding that the number of obese pets, those at least 30 percent above normal weight or a body condition score (BCS) of 5, continues to grow despite 93.4 percent of surveyed pet owners identifying pet obesity as a problem. The study found 24.9 percent of all cats were classified as obese and 21.4 percent of all dogs were obese in 2011. That’s up from 2010 when 21.6 percent of cats and 20.6 percent of dogs were found to be obese. “What this tells us is that more and more of our pets are entering into the highest danger zone for weight-related disorders.” says Ward.

Endocrinologist and fellow APOP Board member Dr. Mark Peterson agrees. “Obesity in dogs and cats is not just the accumulation of large amounts of adipose tissue, but it is associated with important metabolic and hormonal changes in the body. For example, heavy or obese cats are up to four times more likely to develop diabetes as a complication of their obesity. Losing weight can lead to reversal of the diabetic state in some of these obese cats.”

To read or download the complete article and results of the APOP survey, click here.

To learn more about pet obesity or the APOP, go to the Association for Pet Obesity Prevention website.

3 Things You Can Do To Help Your Dog Lose Weight

We are an overweight society and our pets are no different. Over half of American dogs are overweight, and up to 25% are obese.

Dogs with obesity are more prone to a variety of health problems, just like people. These include an increased incidence of diabetes, asthma, and hip and joint problems.

Losing weight can help overweight dogs become healthier and happier. It can also help them to live longer.

Here are some things you can do tomorrow that can help your dog start losing weight.

1. Cut the treats in half. If you must feed treats, cut them in half or give half as many in a day. This can help cut calories. Switching to carrots may help.
2. Exercise your dog more. Ask your vet if your pet is healthy enough to tolerate more exercise. If you play with your dog every day, play a few minutes longer. If you go on a walk, go a little farther. This helps burn calories.
3. Lower the amount of calories your dog consumes each day by changing your dog's food. I like to use diets lower in carbohydrates and higher in protein.

There are several diets formulated for weight loss. Discuss it with your veterinarian to learn more. But remember, whatever diet is chosen, portion control is a big issue.

Although the most common explanation for an overweight pet is simply a lack of exercise and too much to eat. But what if you feed your dog sensibly, exercise adequately, and your dog still has a weight problem?

There could be a number of underlying diseases may be causing your dog to become overweight or obese. Hormonal diseases such as hypothyroidism and Cushing’s syndrome commonly cause weight gain. Steroid pills or tablets with cortisone-like drugs could also be contributing to the obesity.

If these 3 simple hints don't help, ask your veterinarian if an underlying disease could be part of the problem.

Animal Endocrine Clinic March 18 Seminar

We are pleased to announce our second Animal Endocrine Clinic Seminar:

Animal Endocrinology:

Perils and Pitfalls in the Diagnosis and Treatment of Endocrine Diseases 

This seminar will take place on March 18th in Westchester County, NY. AEC Seminars are free and are open to veterinarians and veterinary technicians. The March 18th seminar will deal with several of the most common canine and feline endocrine disorders.

Dr. Mark E. Peterson and Dr. Rhett Nichols will discuss Hyper- and Hypothyroidism, Thyroid and Parathyroid Tumors, Primary Hyperparathyroidism, Idiopathic Hypercalcemia, Diabetes mellitus, Cushing's syndrome, and Hyperaldosteronism.

Further details and the registration form are available here.

World Thyroid Day

Today, May 25th 2011, we recognize the 4th Annual World Thyroid Day.  Established in 2008, World Thyroid Day highlights five major goals to:

• Increase awareness of thyroid health,
• Promote understanding of advances made in treating thyroid diseases,
• Emphasize the prevalence of thyroid diseases,
• Focus on the urgent need for education and prevention programs, and
• Expand awareness of new treatment modalities.

In humans, dogs and cats, the thyroid, a large endocrine gland located in the neck, produces hormones that influence virtually every cell, tissue and organ in the body. The thyroid gland regulates the body's metabolism — the rate at which the body produces energy from nutrients and oxygen — and affects critical body functions, such as energy level and heart rate.

Diseases of the thyroid  gland include hyperthyroidism, hypothyroidism, and thyroid cancer.  These disorders are very common and affect tens of millions of people worldwide. As we all know from reading this blog, the same thyroid diseases are also common in dogs and cats.

For more information, see: www.worldthyroidday.com.

How Do We Treat Dogs With Hypothyroidism?

There is no cure for hypothyroidism, but it is a disease that is easily managed.

The foundation of treatment of dogs with hypothyroidism is thyroid hormone replacement therapy. In other words, we simply replace the missing hormone to restore the dog’s metabolic function back to normal.

However, it’s important that the dog receives the proper thyroid hormone supplement that is given at the appropriate dosage and at the correct intervals to best resolve all of the clinical signs of hypothyroidism.

Thyroid hormone replacement therapy: Which product do we use?

Treatment for hypothyroidism involves lifelong oral medication with levothyroxine (L-T4), a relatively inexpensive synthetic thyroid hormone supplement. These treatments have to be given by mouth, and the supplements are available both as tablets and a liquid formulation. It is important to give the medication at the same time every day (preferably twice daily), and it’s been shown that absorption is better if given on an empty stomach.

Why give L-T4 as the thyroid hormone replacement? As discussed in our last post, thyroxine (abbreviated T4, because it contains 4 iodine molecules) is the hormone produced by the thyroid gland. It is converted primarily in the liver and kidney by an enzyme (deiodinase enzyme) that removes one of the iodine molecules, thereby forming the T3 hormone, which enters the cells. Its function is to regulate the body’s metabolism.  So by giving L-T4, this will be automatically metabolized to all of the other forms of thyroid hormone made in a dog’s body.

Administering thyroid hormone replacement therapy
How and when you administer your dog's thyroid medication will have a tremendous impact on the success of the treatment.

First of all, it is extremely important that the thyroid hormone treatment not be given with food. It is best to administer thyroid medication at least 1 hour before the dog’s meal or at least 3 hours after eating. Many veterinarians are not aware of the fact that absorption of thyroid hormone from the gut is much better when the hormone is given on an empty stomach.

Thyroxine is best given twice per day, in the morning and evening, spaced about 12 hours apart. Dividing the medication into two doses ensures that the dog receives a steady state of thyroid hormone throughout the day, rather than experiencing very high levels shortly after administration and low levels later in the day when only a morning dose is given.

Although most L-T4 medication comes in pill form, there is a liquid available (Leventa; see figure above) that the company suggests just one dose per day. However, I still recommend that the liquid medication be given twice daily for the best results. If your dog is taking liquid L-T4, be sure to discuss the dosing with your veterinarian.

Monitoring the hypothyroid dog’s L-T4 dosage
Regular follow-up blood tests are vital to ensure your dog receives the accurate amount of hormone replacement therapy. Generally blood tests are rechecked approximately 4 to 8 weeks after starting medication and again as needed while the dog’s metabolism adjusts to the therapy. After that, once yearly checks are adequate to ensure that the thyroid hormone level remains in the normal range.

When taken as directed, thyroxine is extremely safe. However, it is important to make sure your dog is receiving the proper dosage based on the variables discussed above, since excessive thyroxine intake can lead to thyrotoxicosis (thyroxine overdose), a condition that needs to be promptly addressed by your veterinarian. Common signs of L-T4 overdosage include excessive thirst and urination, panting, restlessness, and pacing. If this occurs, the L-T4 needs to be stopped for a day or two and the daily dosage lowered accordingly.

Prognosis for canine hypothyroidism
With proper treatment, the long-term prognosis is excellent. However, complete resolution of clinical features of hypothyroidism may take several weeks to months in some dogs.