Thyroid Problems in Your Pets

Patient Expert

While you may be aware of thyroid problems in people, you may not realize that your furry family members are also susceptible to developing thyroid conditions. Hypothyroidism — an underactive thyroid — is more common in dogs, and is known as canine hypothyroidism. Hyperthyroidism — an overactive thyroid — is more common in cats, and is known as feline hyperthyroidism. Let’s take a look at the symptoms, diagnosis, and treatment of thyroid conditions in your pets.

Canine hypothyroidism

Dogs can develop an underactive thyroid gland, the master gland of hypothyroidism. Hypothyroidism is seen in all breeds but is more common in certain breeds, including:

  • Golden retrievers
  • Labradors
  • Doberman pinschers
  • Cocker Spaniels
  • Dachshunds
  • Irish setters
  • Greyhounds
  • Airedale terriers

Hypothyroidism is rarely seen in toy and miniature dog breeds.

Most cases of hypothyroidism are a result of autoimmune disease, where the dog’s immune system attacks and disables the thyroid gland.

Hypothyroidism can affect dogs at all ages but is less common in puppies. Most dogs that are diagnosed with hypothyroidism fall between the ages of 4 and 10. Male and female dogs are at similar risk, but spayed females are at higher risk than unspayed females, mirroring the increased risk of hypothyroidism found in menopausal women.

Symptoms: The symptoms of hypothyroidism in your dog can include:

  • Weight gain with no change in diet or appetite
  • Lethargic or depressed behavior, such as a sleeping more than usual, getting tired when playing or walking, or less interest in playing or exercise
  • Skin rashes and skin infections
  • Dry skin, dry coat, dull coat
  • Hair loss
  • Low blood pressure
  • Swallowing problems
  • Unusually cold, seeking out warmer spots
  • Chronic ear infections
  • Behavioral changes, such as anxiety, obsessiveness, or aggression

Diagnosis: Hypothyroidism is diagnosed in your dog via several evaluations:

  • A physical examination for the signs of an underactive thyroid
  • A review of the dog’s medical history
  • A discussion of the dog’s behavioral changes
  • Blood tests, which typically include thyroid stimulating hormone (TSH), and total thyroxine (total T4)

Treatment: Hypothyroidism in dogs is treated with a daily dose of synthetic thyroid hormone called levothyroxine. The veterinary brand name of levothyroxine is Soloxine.

Some holistic veterinarians use a supplement called Thytrophin PMG from Standard Process to treat canine hypothyroidism. (Note, however, that treating your dog’s thyroid should be done under the supervision of a knowledgeable veterinarian.)

Your dog should be retested within two months to see if the dosage of medication or supplements requires any adjustment. After your dog is stabilized, he or she should have a follow-up evaluation with the veterinarian every 6 to 12 months after starting treatment.

Feline hyperthyroidism

Hyperthyroidism is more common in cats over 10 years old, and some 2 percent of cats typically develop hyperthyroidism. Hyperthyroidism occurs in any breed of cats but seems to be more common in domestic shorthair cats.

Cats who eat canned foods are at greater risk of hyperthyroidism, due to the thyroid-damaging chemical bisphenol-A (BPA) found in the liners of many brands of cat food cans.

If a cat is not treated, hyperthyroidism in cats can cause heart failure or kidney failure and can be fatal.

The main cause of hyperthyroidism in cats is a benign thyroid tumor that releases extra thyroid hormone.

Symptoms: The symptoms of an overactive thyroid in your cat can include:

  • Weight loss
  • Increased appetite with no weight gain
  • Demanding more food and demanding food more frequently
  • Hyperactivity
  • Vomiting and diarrhea
  • Behavioral changes, such as increased vocalization
  • Increased energy and playfulness
  • More vocalization
  • Demanding food more frequently
  • Thirst, drinking more water
  • More frequent urination
  • A diagnosis of feline hypertrophic cardiomyopathy (HCM). The symptoms of HCM can include labored or rapid breathing, breathing with an open-mouth, or lethargy and excessive sleeping.

Diagnosis: Hyperthyroidism is diagnosed in your cat via several evaluations:

  • A physical examination for the signs of an overactive thyroid
  • A review of your cat’s medical history
  • A discussion of your cat’s behavioral changes
  • Blood tests, which typically include thyroid stimulating hormone (TSH), and total thyroxine (total T4)

Treatment: In the past, feline hyperthyroidism was treated with surgery to remove the thyroid gland, but that is less common. One popular treatment is daily oral antithyroid medication — typically the drug methimazole (brand name Tapazole) — for life. The typical cost of antithyroid drug therapy is $25 to $30 a month for life. The challenge of medication is that it may be difficult to get your cat to take a daily pill, and methimazole can cause vomiting as a side effect in cats. Once the hyperthyroidism is resolved with medication, your cat should have a follow-up evaluation with the veterinarian every 6 to 12 months after starting antithyroid drug treatment.

Veterinarians consider radioactive iodine (RAI) treatment to be the safest and best treatment for feline hyperthyroidism. Your cat will be hospitalized and given a radioactive iodine injection, then kept in the hospital for about a week until they are no longer radioactive. There is a network of feline hyperthyroidism treatment centers around the United States called Radiocat that provides information about RAI for cats, as well as contact information for local veterinarians who offer this treatment. RAI usually resolves the feline hyperthyroidism but can be somewhat expensive, costing from around $1,000 to up to $1,500.

Another option is the use of a specialized low-iodine food. Hill's Pet Nutrition, for example, created a prescription low-iodine food for cats, called y/d Feline, which may resolve hyperthyroidism in some cats.


Cornell College of Veterinary Medicine — Feline Health Center

Cornell College of Veterinary Medicine — Canine Health Center

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