Thyroid Conditions in Cats

The thyroid gland is a small butterfly-shaped gland located in the cat's throat, cradling the windpipe. It is responsible for producing thyroxine, or T4, and triiodothyronine, or T3, two hormones that regulate the cat's metabolism. The pituitary gland produces thyroid stimulating hormone, or TSH, which controls the production of T4 and T3. If either of these glands is out of sync, too much or too little thyroid hormone is released.

  1. Types

    • The two types of thyroid disorders are hyperthyroidism, in which too much thyroid hormone is produced, and hypothyroidism, which involves too little of the hormone. According to PetEducation.com, hyperthyroidism is the most common hormonal disorder affecting cats. Hypothyroidism is a much more rare condition in cats, and is commonly seen in cats that have undergone surgery for hyperthyroidism.

    Cause and Occurrence

    • Abnormal growths in the thyroid gland typically cause hyperthyroidism, and according to PetEducation.com only one or two percent are cancerous. Male and females of any breed between the ages of four and 22 are at risk for developing hyperthyroidism, with most cases occurring after the age of eight. Hypothyroidism can occur naturally in older cats in rare circumstances, but most cases develop due to hyperthyroidism treatment. Surgery is performed in the thyroid gland to prevent excessive production, causing it to become under active.

    Symptoms

    • In almost all instances, symptoms of hyperthyroidism and hypothyroidism are polar opposites. Weight loss, hyperactivity and diarrhea are symptoms of hyperthyroidism; weight gain, lethargy and constipation indicate hypothyroidism. Both conditions share loss of appetite and poor coat appearance as symptoms, however.

    Diagnosis

    • Either condition requires testing and physical examination. Hyperthyroidism and hypothyroidism can exhibit a mass in the thyroid gland itself, which your veterinarian can feel as he or she examines your cat. Blood tests are performed to check T3 and T4 levels.

    Treatment

    • Hyperthyroidism is treated by daily anti-thyroid medications to block hormone production, surgery to remove the abnormal growths or the gland itself or radioactive iodine, which kills the abnormal cells. Hypothyroidism is treated with hormone replacement therapy, in which drugs such as levothyroxine and methimazole mimic the reaction of the naturally occurring hormones T4 and T3.