Tuesday, May 7, 2013

Feline Hyperthyroid Disease And How We Treat It.

An increase in the thyroid hormone activity in the cat’s thyroid gland is known as Hyperthyroidism. It is usually caused by a benign tumor in one or both of the cat’s thyroid glands. There is only a 5% chance that a benign tumor can become malignant. 
A benign tumor is contained to the place it is growing, while a malignant tumor can spread out or seed itself in different and distant organs.  
Symptoms of Hyperthyroidism in Cats
Not all symptoms will be seen in every cat with hyperthyroidism, but any one or two of them should be a strong indication that a veterinary examination is indicated. Some or all of the following symptoms may be present in a hyperthyroid cat:

·         Increased Appetite
·         Unexplained Weight Loss and loss of muscle mass
·         Irritability or Nervousness
·         Frequent Vomiting

Typically thin cat with a large appetite
·         Unkempt-looking Coat
·         Diarrhea
·         Excessive Thirst (polydipsia)
·         Weakness  
·         Lethargy

Thyroid hormones affect nearly all the organs in the body; therefore, thyroid disease can sometimes cause secondary problems. Thyroid hormones stimulate a faster heart rate and a stronger contraction of the heart muscle. Over time, cats with hyperthyroidism may develop an enlargement and thickening of the left ventricle of the heart. If left untreated and unmanaged, these changes will eventually compromise the normal function of the heart and can even result in heart failure. This means that in some cats with hyperthyroidism, additional treatment may be required to control secondary heart disease. However, once the underlying hyperthyroidism has been controlled, the cardiac changes will often improve or may even resolve completely.

Hypertension-high blood pressure-is another potential complication of hyperthyroidism and can cause additional damage to several organs, including the eyes, kidneys, heart, and brain. If hypertension is diagnosed along with hyperthyroidism, drugs may be needed to control the blood pressure and reduce the risk of damaging other organs. As in the case of heart disease, after the hyperthyroidism has been successfully treated, the high blood pressure will often resolve, and permanent treatment for it may not be required.


Three basic treatments each offer a strong possibility of returning the thyroid gland to normal function.  They are medication, surgery, and radiation therapy.

Anti-Thyroid Medication

This is almost always the first treatment. It is non-invasive, inexpensive, and the only choice for cats with kidney or heart disease. It comes in pills and trans-dermal ointments for easy administration. The medication will control the production of thyroid hormones.

Medication usually is given once or twice daily for life with regular blood tests to regulate dosage.
Additionally, there is also a prescription diet called Hill's Y/D which can reduce hyperthyroid disease to varying degrees.


Surgery is an effective treatment, but it is best done by a veterinarian skilled in this type of surgery, called a "thyroidectomy." Surgery is most often indicated when only one thyroid lobe is involved. A radionuclide scan is indicated prior to the surgery to determine the extent of the diseased thyroid tissue, and to locate any extraneous thyroid tissue growing elsewhere in the neck (or chest) of the cat, which may contraindicate surgery.

Some advantages to this type of treatment are: It eliminates the need for long-term medication, and  It is favored where Radioactive Iodine Therapy (I131) is not available.


Radioiodine Treatment
This is quickly becoming the treatment of choice in areas where it is available, and where the caregivers can afford it. A single injection of radioactive iodine (R131) is given subcutaneously. The substance "finds" and destroys all diseased tissue, including any ectopic thyroid cells without harming any normal tissue. The cat must remain in the veterinary hospital for five days to two weeks (depending on state laws) until his radioactive levels are acceptable. Caregivers may be able to visit during that time, but will only be able to view their kitty through a special leaded window.
The advantages to Radioiodine are that it provides a permanent cure in 95% of cases. It is safe and minimizes stress to the cat. The expense can be the same as surgery. Additionally, the cat must be in good health.

There are several good treatments to control Hyperthyroid disease. The first step is to take your cat into your veterinarian for an annual wellness exam. It all starts with the discovery of the disease.

The Providence Veterinary Hospital Blog is a publication of Peter Herman, VMD, at the Providence Veterinary Hospital, 2400 Providence Ave. in Chester, PA. Contact Dr. Herman at 610-872-4000 or visit us at http://www.providencevet.com.