Hyperthyroidism vs. Hypothyroidism

Humans can experience the effects of both Hyperthyroidism and Hypothyroidism. In their basic definitions, these diseases represent the over and under production of the thyroid hormone. Our furry friends provide an exception to the traditional human definition of Hyper or Hypo-thyroidism; cats typically experience hyperthyroidism and dogs typically experience hypothyroidism. In plainer terms, cats experience the over production of the thyroid hormone and dogs experience the under production of the thyroid hormone. These diseases are commonly diagnosed in veterinary medicine, so I hope to shed some light on the details for pet parents.

Where is the thyroid hormone?

The thyroid hormone is located on the neck for both cats and dogs. According to the Merck/Merial Manual for Pet Health, the thyroid gland produces the same two hormones as the human thyroid gland T3 and T4. The thyroid hormone is central to the animal metabolism, and works in harmony with many other hormones throughout the body. If you bring your cat to the veterinarian and they feel along the center of their neck, they are feeling for their thyroid hormone. When cats have hyperthyroidism, their thyroid gland sometimes becomes noticeably larger. Because this swelling isn’t always evident, blood work is the most common form of diagnosis.



What is Hyperthyroidism?

The definition of hyperthyroidism according to the Merck/Merial Manual for Pet Health, is the excess production of the T3 and T4 hormones. The most common cause of feline hyperthyroidism is a benign thyroid tumor.

What are the symptoms of Hyperthyroidism?

According to the Merck/Merial Manual for Pet Health the symptoms include:

Weight loss: This is why it is important to bring your pet in for their annual exam. They could have lost 2lbs in the last year, that you may not have noticed, and they could be experiencing internal symptoms. 
Excessive Appetite: Have you ever met a kitty who will physically harass you for food? If this is a new behavior, you might want to have their thyroid hormone tested.
Hyper-excitability: Many hyperthyroid cats become VERY vocal and what some owners describe as “needy”. 
Increased Thirst/Urination/Defecation: All of these symptoms are associated with an increase in metabolism. 
Vomiting/Diarrhea: May be due to the inefficiencies within the system as a result of the overproduction of the thyroid hormone.  
Cardiovascular symptoms include heart murmurs, shortness of breath, and congestive heart failure. 

What treatments are available for Hyperthyroidism?

Radioactive iodine treatment: According to the Centers for the Treatment of Feline Hyperthyroidism radioactive iodine treatment is advantageous due to its cost effective nature, and lack of anesthesia. 
Surgical Removal of the Thyroid Gland: According to VeterinaryPartner.com, surgical removal of the gland is advantageous due to its effectiveness. Often times, no additional treatment is necessary.
Long term medications: This is the most common treatment chosen by pet owners. I believe many people choose this option based on the age of their cat versus the expense of the other options. These days, pharmacy companies have the option of medicated chews for your cat, which is much easier that physically pilling them.

Can dogs ever experience hyperthyroidism?

According to the Merck/Merial Pet Manual for Health, the answer is Yes, although very rarely.


What is hypothyroidism?

According to the Merck/Merial Manual for Pet Health hypothyroidism causes decreased levels of thyroid hormone result in a slower metabolic rates. Hypothyroidism is most common in 4 to 10 year old mid to large breed dogs.

What are the symptoms of hypothyroidism?

Lethargy or unwillingness to exercise due to a decrease in metabolism.
Weight gain without an increase in food intake.
Dryness of skin and coat.
Excessive shedding.

What treatments are available?

According to Pet.WebMD.com the only treatment available is to treat with thyroid replacement hormone medication. Typically, the treatment is lifelong and thyroid hormones should be monitored throughout a dogs life.

Can cats ever experience hypothyroidism?

Yes, typically as a result of the damage or removal of the thyroid gland.

Many of these symptoms can be discussed at your pet’s annual exam. Be sure to note any changes in their weight and appetite.

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