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Cat Hypothyroidism

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Signs and Symptoms

Cat hypothyroidism is quite a rare disease, especially compared to cat hyperthyroidism, but it does still occur. This endocrine disorder stems from improper function of the thyroid gland, which is responsible for producing hormones that play a significant role in a number of physiological pathways. While hypothyroidism is not a life-threatening disorder, it can greatly detract from your cat's comfort and quality of life. For this reason, it's important to have this condition diagnosed as soon as possible so that your pet can undergo treatment and enjoy restored health.

Since hypothyroidism alters metabolism and has an effect on many different organs and physiological functions, potential symptoms of this disorder are numerous, varied, and often non-specific. Thus, one single symptom is not enough to suggest hypothyroidism to a veterinarian, but a combination of several warning signs will raise suspicions of this endocrine disease. Two very common symptoms of feline hypothyroidism are weight gain and lethargy. A cat suffering from this disorder may also appear to become mentally dull in addition to physical sluggishness. These symptoms may, in turn, lead to decreased interest in play or other daily activities as well as more time spent sleeping.

The hair-producing cells of a cat with hypothyroidism begin to slow down as a result of this disorder, and this means that the animal will experience less new hair growth. With time, the cat's hair will lose its shine, become greasy, and begin to fall out. Bald patches often appear on the animal's trunk and it's also common for a cat with this condition to develop a bald tail, except for a tuft of fur at the very tip. Unhealthy skin is also typical of cats with hypothyroidism. This leads to greasy dandruff as well as recurring skin infections. In some cases, cats with hypothyroidism will become uncoordinated, suffer from seizures, or become infertile.

If one or more of these symptoms describe what you are observing in your cat, contact a veterinarian. Any combination of these warning signs and behaviors could indicate that your pet is suffering from hypothyroidism or another medical condition. A veterinarian will be able to identify the cause of your cat's symptoms and will help you to implement a treatment plan.


Feline hypothyroidism is not always an easy condition to diagnose; a number of tests may be required in order to confidently confirm the presence of this disorder in a feline patient. To begin with, a veterinarian will take a complete medical history, perform a physical examination, and document clinical signs. Once these steps have been completed, a number of tests may be run. Typically, a veterinarian will order blood tests that will allow for an evaluation of the feline patient's biochemical profile as well as a complete blood count (CBC). Urinalysis may also be performed.

Thyroid tests will also be conducted when checking for hypothyroidism in a cat. While the levels of the hormone tri-iodothyronine (T3) may be checked, thyroxine (T4) and free T4 tests tend to be the most helpful with regards to diagnosing this thyroid disorder. A special test known as a TSH stimulation test may also be performed. If a cat does indeed have hypothyroidism, this test will show that T4 levels do not increase when the feline patient is given TSH (thyroid stimulating hormone). Other potential diagnostic tools include x-rays and EKG. Some cats with hypothyroidism also suffer from a condition known as megacolon, where their large intestine is dilated and filled with stool. Abdominal x-rays will allow a veterinarian to see whether or not a cat has this problem. With regards to EKG, slow heart rates and abnormal heart tracings with low R waves are common amongst felines with hypothyroidism.


A cat's thyroid is a butterfly-shaped gland with two lobes, located in the animal's neck near its larynx. The thyroid is controlled by the pituitary gland, which uses thyroid stimulating hormone to cause the thyroid to produce and release the hormones thyroxine (T4) and tri-iodothyronine (T3). These thyroid hormones play a significant role in numerous physiological functions and affect nearly every organ in the cat's body. Two of the chief responsibilities of these hormones are the regulation of growth and the regulation of metabolism. In fact, the thyroid is responsible for determining how fast every cell in the body burns energy. It's because the thyroid has such a widespread effect on a cat's body that the symptoms of hypothyroidism are so varied and involve the animal's entire system.

As mentioned previously, hyperthyroidism is far more common amongst cats, but feline hypothyroidism does occur. When a cat is suffering from hypothyroidism, its thyroid produces less thyroxine (T4). As a result, the levels of this hormone in the cat's system become deficient. This deficiency then has an effect on all of the functions and pathways in which T4 is involved. Metabolism, heart rate, and activity levels all slow down, giving rise to several of the common symptoms of this endocrine disorder. Furthermore, many other effects are felt by the cat, as every cell in its body experiences the consequences of low thyroxine levels. Since a cat's thyroid acts as a master gland and has control over so many systems, it's not surprising that the symptoms and warning signs of improper thyroid function are so numerous and diverse.


Feline hypothyroidism can be caused by a variety of factors, but most causes are iatrogenic. This means that cat hypothyroidism is usually caused by a physician through some form of medical treatment or procedure. Particularly, there are a number of treatments for feline hyperthyroidism that can ultimately end up triggering hypothyroidism. For example, the surgical removal of a cat's thyroid glands (thyroidectomy) in order to treat hyperthyroidism can lead to hypothyroidism. Similarly, use of radioactive iodine or an antithyroid drug such as methimazole to treat hyperthyroidism can also result in deficient production of thyroxine.

While extremely rare, there are a few potential non-iatrogenic causes of cat hypothyroidism. For example, thyroid tumors (neoplasia) that affect both lobes of the thyroid and destroy the entire gland can potentially trigger hypothyroidism. A dietary deficiency of iodine is another potential cause of this endocrine disorder. However, commercial brands of cat food generally contain sufficient dietary iodine so, again, this is a very rare cause of hypothyroidism. Finally, congenital forms of feline hypothyroidism are also extremely rare, but do occur. Known causes of congenital forms of this disorder include an inability of the gland to respond to thyroid stimulating hormone (TSH) and a defect in thyroid hormone biosynthesis that is internal to the thyroid gland (dyshormonogenesis).


While feline hypothyroidism can be tricky to diagnose, it's relatively easy to treat. For cases caused by use of an antithyroid drug such as methimazole, administration of the drug will be discontinued until T4 levels return to normal, which could take several days. Then the drug will be reintroduced at a lower dosage. For most other forms of hypothyroidism, hormone supplementation is the typical treatment. This involves administering thyroxine as an oral medication either once or twice a day. Cats are started out on a low dosage which is then increased incrementally in order to allow the animal's heart to adjust.

Generally, once hormone supplementation is begun, the first signs of improvement appear within the first two weeks. Cats become more alert and active quite quickly and often begin to lose weight within two to four weeks of the start of treatment. Skin and hair problems tend to resolve over the first two months. If hormone supplementation is required for a feline patient, the cat will need to receive the medication for the rest of its life in order to keep the condition from reoccurring.

Many cats also benefit from a number of different homeopathic forms of treatment. Kelp and seaweed containing iodine are known to benefit some cats with hypothyroidism, while others respond well to alfalfa, oats, parsley, and fennel. Vitamins are also recognized for their benefit to cats with this thyroid disorder, especially vitamin A, C, and the B vitamins. Omega 6 fatty acids are also helpful, especially for those cats with weakened or sluggish immune systems.

There are also homeopathic remedies available in the form of herbal tonics that can be very helpful with respect to treating feline hypothyroidism. These tonics contain a variety of natural ingredients which combine to provide a number of positive effects. For instance, kelp supplies iodine and also stimulates the thyroid gland while gotu kola helps to balance hormones. Furthermore, watercress and papaya are nutritionally beneficial while licorice and milk vetch boost the immune system. By combining a number of these natural substances into one product, herbal tonics are capable of providing a variety of beneficial effects that can be of great help when trying to treat feline hypothyroidism.

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