cat hyperthyroidism

Hyperthyroidism in Cats: Symptoms and Treatment

Diane Weinmann Animal Health, animal hospice , , , , ,

Hyperthyroidism in Cats: Symptoms and Treatment

by: Dr. Lorie Huston as seen in PetMD 

 Reviewed and updated on March 18, 2020, by Jennifer S. Fryer, DVM

 

Hyperthyroidism in cats is a disease that’s usually caused by a benign tumor within the thyroid gland. This tumor causes an overproduction of the thyroid hormone called thyroxine. One of the primary functions of this thyroid hormone is to regulate an animal’s metabolism. 

Cats with too much thyroid hormone have a greatly increased metabolic rate, which leads them to lose weight despite having a ravenous appetite. Other symptoms can include anxiety, vomiting, diarrhea, and increased thirst and urination.

These excessive hormone levels push a cat’s body into constant overdrive, which frequently leads to high blood pressure and a type of heart disease called hypertrophic cardiomyopathy. 

Here’s everything you should know about hyperthyroidism in cats so you can spot the signs and get your cat on a treatment plan as soon as possible.

How Common Is Hyperthyroidism in Cats? 

There is no known genetic predisposition for hyperthyroidism, but it is quite common in cats. 

In fact, hyperthyroidism is the most common hormonal (endocrine) disease in the cat population, often seen in late middle-aged and older cats. 

The average age of diagnosis is approximately 13 years. The possible age range is 4-20 years, although seeing young hyperthyroid cats is very rare.

What Does the Thyroid Gland Do?

In cats, the thyroid gland has two parts, with one on each side of the trachea (windpipe), just below the larynx (voice box).

The thyroid gland makes several different hormones (mostly thyroxine, or T4). These thyroid hormones affect many of your cat’s body processes:

·         Regulation of body temperature

·         Metabolism of fats and carbohydrates

·         Weight gain and loss

·         Heart rate and cardiac output

·         Nervous system function

·         Growth and brain development in young animals

·         Reproduction

·         Muscle tone

·         Skin condition

Symptoms of Hyperthyroidism in Cats

Here are the major symptoms of hyperthyroidism that you should look for in your cat:

·         Weight loss

·         Increased appetite (ravenous)

·         Unkempt appearance

·         Poor body condition

·         Vomiting

·         Diarrhea

·         Drinking more than usual (polydipsia)

·         Peeing more than usual (polyuria)

·         Rapid breathing (tachypnea)

·         Difficulty breathing (dyspnea)

·         Heart murmur; rapid heart rate; an abnormal heartbeat known as a “gallop rhythm”

·         Hyperactivity/restlessness

·         Aggression

·         Enlarged thyroid gland, which feels like a lump on the neck

·         Thickened nails

Less than 10% of cats suffering from hyperthyroidism exhibit atypical signs such as poor appetite, loss of appetite, depression, and weakness.

What Causes Cats to Be Hyperthyroid?

Hyperfunctioning thyroid nodules (where the thyroid nodules produce excess thyroid hormones outside of the control of the pituitary gland) cause hyperthyroidism. But what causes the thyroid to go haywire?

 

There are several theories about what causes cats to become hyperthyroid:

·         Rarely, thyroid cancer

·         Some reports have linked hyperthyroidism in cats to some fish-flavored canned food diets

·         Research has pointed to flame-retardant chemicals (PBDEs) that are used in some furniture and carpeting and circulated in house dust

·         Advancing age increases risk

How Do Vets Test for Feline Hyperthyroidism?

In most cases, diagnosing hyperthyroidism is straightforward: high levels of thyroid hormone in the bloodstream (total T4 or TT4) along with the typical signs. 

In some cases, however, your cat’s T4 levels may be in the normal range, making a diagnosis of hyperthyroidism more difficult. This is especially true in the early stages of this disease. 

If your cat is showing the symptoms of hyperthyroidism but the blood tests are not conclusive, you will need to return to your veterinarian for further blood tests or for a referral for a thyroid scan.

The signs of feline hyperthyroidism can also overlap with those of chronic renal failure, diabetes mellitus, chronic hepatic disease, and cancer (especially intestinal lymphoma). 

These diseases can be excluded on the basis of routine laboratory findings and thyroid function tests. Your veterinarian will conduct a battery of tests to zero in on a reliable diagnosis.

Kidney disease is commonly diagnosed along with hyperthyroidism in cats. Cats suffering from both diseases may need treatment for both, and the diagnosis of kidney disease in a cat with hyperthyroidism can affect the cat’s prognosis. 

Treatment for Hyperthyroid Cats

The gold standard therapy is radioiodine (I131) treatment, which can cure the hyperthyroidism in most cases. Daily medication (methimazole) or feeding a low-iodine diet are good options when radioiodine therapy is not an option due to financial considerations or the cat’s overall health.

Radioiodine Therapy (Radioactive Iodine Treatment)

Radioiodine therapy, or I131 treatment, uses radioactive iodine to kill the diseased tissue in the thyroid gland. Most cats undergoing I131 treatment are cured of the disease with one treatment.  

The cat’s thyroid levels are monitored after treatment. Rare cases require a second treatment. Hypothyroidism is not common after treatment, but it can occur, and it can be managed with a daily thyroid medication.

The use of radioiodine is restricted to a confined medical facility, since the treatment itself is radioactive. Depending on the state you live in and the guidelines in place, your cat will need to be hospitalized from several days to a few weeks after being treated with radioactive medicine, to allow the radioactive material to leave your cat’s body before coming home.

Precautions will still need to be taken after bringing your cat home. Your veterinarian will give you specific instructions to reduce your risk of exposure to the radioactive material, which will probably include storing your cat’s used litter in a sealed container for a period of time before disposing of it in the garbage.

 

Surgically Removing the Thyroid Gland

Surgical removal of the diseased thyroid gland is another potential treatment. Like I131 treatment, surgical treatment is curative, but these cats also must be monitored afterward for hypothyroidism.

Surgical removal of the thyroid gland is best performed when only one thyroid gland is affected, as removal of both can possibly lead to hypothyroidism. Another complication that can occur after surgical removal of the affected thyroid gland is the successive hyperactivity of the remaining thyroid gland.

Methimazole Medication

Giving your cat a medication called methimazole is probably the most common treatment choice. It’s administered by mouth in pill form, or it can be formulated by a compounding pharmacy into a transdermal gel that can be applied to your cat’s ear. Methimazole is often given before radioiodine treatment or surgery to stabilize your cat’s clinical signs.  

Methimazole is effective in controlling the symptoms of hyperthyroidism. However, it does not cure the disease—your cat will need to receive the medication for the rest of his life. If a cat is younger at diagnosis (under 10 years old) and does not have underlying diseases, the cost of methimazole for a lifetime may exceed surgery or radioiodine. 

Methimazole has rare but significant side effects in some cats, so make sure to make and keep regular monitoring appointments with your veterinarian. 

Iodine-Restricted Diet

 

Feeding a diet that restricts iodine is a newer alternative for treatment of feline hyperthyroidism. Like methimazole treatment, this alternative is not curative, and your cat will require lifelong treatment. 

This diet must be given exclusively. The hyperthyroid cat on this diet must not have access to or be given any treats, other cat food, or human food. Other cats in the household may eat this food, but they must be supplemented with an appropriate cat food for their age and health in order to provide adequate iodine. 

Follow-Up Care for Hyperthyroid Cats

Once treatment has begun, your veterinarian will need to reexamine your cat every two to three weeks for the initial three months of treatment, with a complete blood count to check their T4. Treatment will be adjusted based on the results, such as changing methimazole dosage to maintain T4 concentration in the low-normal range.

If your cat has had surgery, particularly removal of the thyroid gland, your veterinarian will want to closely observe your cat’s physical recovery. Development of low blood-calcium levels and/or paralysis of the voice box during the initial postoperative period are complications that will need to be watched for and treated, should they occur. 

Your doctor will also measure your cat’s thyroid hormone levels in the first week after surgery and every three to six months thereafter, to check for recurrence of thyroid gland overactivity. 

By: Dr. Lorie Huston, DVM, Dr. Jennifer Coates, DVM, Dr. Jennifer S. Fryer, DVM

 

Thyroid Dysfunction

Diane Weinmann Animal Health, animal hospice , , , ,

By Dr. Dodds DVM

Thyroid Dysfunction is the most frequently recognized endocrine disorder of pets and it’s often difficult to make a definitive diagnosis, since many clinical signs mimic those resulting from other causes.

 

Dogs

Hypothyroidism is the most common endocrine disorder of canines. Nearly 90 percent of canine cases result from autoimmune thyroiditis. The heritable nature of this disorder poses significant genetic implications for breeding stock.
Common symptoms to look for in dogs:

  • Scratching  •  Hair loss  •  Seizures  •  Chronic bowel issues • Seizures in adulthood  •  Chewing feet and skin  •  Skin and ear infections  • Behavioral changes: aggression, moodiness, phobias

Cats
Hyperthyroidism in readily induced, especially in geriatric cats, by feeding commercial pet foods, treats and snacks containing excessive amounts of iodine. This finding has led to a major change in the iodine formulations of feline commercial pet foods.

Common symptoms to look for in cats:
Pacing  •  Anxiety  •  Phobias   •  Howling  •  House soiling  • Insatiable hunger  •  Dementia with aging  •  Hunger and weight loss

Hyperthyroidism in Cats

Diane Weinmann Animal Health, animal hospice, healing your pet , , , ,

Hyperthyroidism in Cats

By Dr. Karen Becker

Recent research has revealed that yet another chemical substance found in households may be contributing to feline hyperthyroidism, a disease that affects a significant percentage of cats over the age of 10. The chemicals are called per- and polyfluoroalkyl substances (PFAS), and they are widely used as water and oil repellents. According to ScienceDaily:

“PFAS are a family of more than 3,000 structures of highly fluorinated chemicals used in industrial processes and consumer products, such as protective coatings for carpets, furniture and apparel, paper coatings, insecticide formulations, and other items.”1

PFAS are used in many industrial applications calling for nonstick or slick surfaces, such as food packaging, stain- and water-resistant fabrics, nonstick cookware and firefighting foam. These chemicals are now ubiquitous in our environment, having migrated into the air, household dust, food, soil, and ground, surface and drinking water.

Study Links PFAS Chemicals to Hyperthyroidism in Cats

For the study, a team of researchers at the California Environmental Protection Agency looked at blood levels of PFAS in two separate groups of Northern California kitties, most of which were at least 10 years old. The first group of 21 was evaluated between 2008 and 2010; the second group of 22 was sampled between 2012 and 2013.2

The researchers observed that the higher the blood levels of PFAS, the more likely the cat was to be hyperthyroid. One type of PFAS in particular, perfluorooctanoic acid (PFOA) was significantly higher in hyperthyroid kitties. These findings “… may indicate a possible link between PFAS levels and cat hyperthyroid, warranting a larger study for further investigation,” according to the research team.

In a bit of good news, the scientists noted a slight decline in PFAS blood levels between the first group of cats tested eight to 10 years ago, and the second group tested more recently. This mirrors recent results in humans as more companies phase out use of these chemicals, and presumably, as people gradually replace PFAS-treated household items.

Reducing Your Family’s and Pet’s Exposure to PFAS

Your best bet is to avoid all products that contain or were manufactured using PFAS, which will typically include products that are stain-resistant, waterproof or nonstick. From the Environmental Working Group:3

Find products that haven’t been pre-treated and skip optional stain-repellent treatment on new carpets and furniture
Cut back on fast food and greasy carryout food, since these foods often come in PFC-treated wrappers
Especially when buying outdoor gear, choose clothing that doesn’t carry Gore-Tex or Teflon tags, and be wary of all fabrics labeled stain- or water-repellent
Avoid nonstick pans and kitchen utensils — opt for stainless steel or cast iron instead
Pop popcorn the old-fashioned way, on the stovetop, since microwaveable popcorn bags are often coated with PFCs on the inside.
Choose personal care products without “PTFE” or “fluoro” ingredients; also avoid Oral-B Glide floss, which is made by Gore-Tex

It’s also important to filter your pet’s drinking water, and yours, to remove contaminants such as fluoride, chlorine, heavy metals and others. Household tap water typically contains enough toxic minerals, metals, chemicals and other unhealthy substances to damage your pet’s health long term.

Flame Retardants: Another Enemy of Indoor Kitties

Polybrominated diphenyl ethers (PBDEs), or flame retardants, are another type of household chemical that has been linked to overactive thyroid in cats, and a 2017 study confirmed the results of earlier studies that prove the high levels of PBDEs measured in indoor kitties are from house dust.4

PBDEs have been used since the 1970s in textiles, electronics and furniture to prevent them from burning, but like PFAS, they aren’t chemically bound to the product material, so they drift into the environment and cling to particles in the air such as house dust.

A number of these chemicals have been banned for use in household products, but they are extremely persistent and can leach into the environment for many years. Contaminated household dust can be inhaled as well as ingested, and can have an adverse effect on the health of kitties.

Brominated Flame Retardants Are Known Endocrine Disruptors

Prior studies of PBDE blood levels in cats have focused primarily on potential causes of feline hyperthyroidism, however, the intent of this study was to measure levels in healthy cats to establish their dust exposure.

The researchers took “paired samples” from the homes of each of the cats, meaning they took both dust samples and blood samples at the same time. They found evidence not only of brominated and chlorinated contaminants currently in use, but also chemicals that have been banned for decades. According to study co-author Jana Weiss, Ph.D.:

“By taking paired samples, we have greater insight into the environment that the cats live in. Moreover the cats in the study spent the majority of their time indoors and therefore air and dust in the home is expected to contribute more than the outdoor environment.”5

The study results are a heads up not only for cat guardians, but also anyone with small children, because both kitties and kiddos engage in a lot of “hand-to-mouth activities.”

“The brominated flame retardants that have been measured in cats are known endocrine disruptors. It’s particularly serious when small children ingest these substances because exposure during development can have consequences later in life, such as thyroid disease,” said Weiss.

Minimizing PDBE Exposure at Home

Most new foam products are not likely to have PBDEs added. If you have foam items in your home, office or vehicle that were purchased before 2005, however, they probably contain PBDEs. The Environmental Working Group offers the following tips to help limit your family’s and pet’s exposure to PBDE-containing products:6

Whenever possible choose PBDE-free electronics and furniture; PBDEs shouldn’t be in mattresses, couches and other foam products sold in 2005 or later, however they’re still put in some new televisions and computer monitors
Avoid contact with decaying or crumbling foam that might contain fire retardants, including older vehicle seats, upholstered furniture, foam mattress pads, carpet padding and kid’s products made of foam
Use a high-efficiency particulate air (HEPA) filter vacuum cleaner, since these vacuums capture the widest range of particles and are also good for reducing lead or allergens in house dust
Replace couches, stuffed chairs, automobile seats and the like that have exposed foam (if you can’t afford to replace them, cover them with sturdy cloth and vacuum around them frequently)
Don’t reupholster your older foam furniture, especially in homes where children or pregnant women live
Be careful when removing or replacing old carpet, since PBDEs are found in the foam padding beneath carpets; isolate the work area with plastics, and avoid tracking construction dust into the rest of your house
The replacement chemicals for PBDEs in foam are not fully tested for their health effects, so buy products made with natural fibers (like cotton and wool) that are naturally fire-resistant and may contain fewer chemicals

Did You Know PBDEs Are Also in Commercial Cat Food?

The same researchers who published the 2017 study I mentioned earlier also measured PBDE levels in cat food (both canned and kibble) matching the diets of the kitties in the study. They found that blood levels of PBDEs in the cats also significantly correlated with concentrations of those chemicals in the cat food.

In addition, another recent study concluded that fish-flavored cat food is a problem.7 A team of Japanese scientists evaluated cat food and feline blood samples and discovered that the type of polychlorinated biphenyl (PCB) and PBDE byproducts found in both the food and blood samples are derived from marine organisms.

The researchers were also able to simulate the way in which the bodies of cats convert the type of chemical present in the food into the type of chemical seen in the cats’ blood samples.

Based on their results, the team concluded the byproducts detected at high levels in cats’ blood samples likely came from fish-flavored food and not exposure to PCBs or PBDEs. However, further work is needed to determine the link between the metabolites (byproducts) and hyperthyroidism. If you’re wondering how these chemicals wind up in fish-flavored cat food, Dr. Jean Hofve of Little Big Cat explains it very well:

“There is a link between the feeding of fish-based cat foods and the development of hyperthyroidism, which is now at epidemic levels. New research suggests that cats are especially sensitive to PBDEs … [which are] found at higher levels in both canned and dry cat foods than dog foods; and more in dry than canned cat foods.

Fish-based foods are even worse, because marine organisms produce PDBEs naturally and can bioaccumulate up the food chain to high levels in fish; this compounds the exposure cats get from fabrics and dust.”8

5 Tips to Help Prevent Hyperthyroidism in Your Cat

  1. Rid your environment of flame-retardant chemicals
  2. Provide an organic pet bed
  3. Feed a nutritionally balanced, fresh, species-appropriate diet to control iodine levels in your cat’s food, since iodine has also been linked to hyperthyroidism
  4. Avoid feeding your cat a fish-based diet, since seafood is a very rich source of iodine, and cats aren’t designed to process a lot of iodine
  5. Avoid feeding soy products to your kitty, as they have also been linked to thyroid damage

I also recommend checking your cat’s thyroid levels annually after the age of 7.