Hyperthyroidism - October 2020

This month’s article is about Hyperthyroidism in cats. This is a common condition in the middle-aged to geriatric feline, which has many effects on the body if left untreated. The disease is usually caused by a benign growth on one or both of the thyroid glands or overgrowth of the gland itself. Rarely, a malignant tumor is found to be the cause of hyperthyroidism.

The effects on the body due to the disease are as follows. Metabolism is increased, leading to increased hunger and thirst. Weight loss is seen despite the increased appetite. Systemic blood pressure is likely to be high due to the increased levels of thyroid hormone in the body. The increased blood pressure can cause damage to the retinas in the eyes. The heart muscle can be thickened and the heart valves may be not functioning normally, resulting in a heart murmur. The heart rate increases and uncommonly there may be an arrhythmia heard. In worst cases of heart disease due to hyperthyroidism, congestive heart failure can result. Other diseases may be concurrent with this condition as well, leading to more complications.

What does the owner of a cat see if his or her kitty has hyperthyroidism? As mentioned before, lots of eating and weight loss despite the good appetite. Increased drinking of water and urination are also seen. Vomiting and/or diarrhea may be a complaint as well. The pet may be hyperactive or often nervous. In more advanced cases, weakness, lethargy, panting, and decreased grooming activity may be seen.

Diagnosis of the condition is relatively simple. If the cat is found to have a higher than normal thyroid level, it is hyperthyroid. Additional testing and other investigation may be needed to confirm any complications or effects that the disease is causing in the body. Other blood work may be performed to determine other systemic changes. Blood pressure may be measured to detect systemic hypertension. Thoracic x-rays may be taken if heart disease is suspected, etc.

There are four therapies used for the treatment of hyperthyroidism. The drug Methimazole is used as a twice daily medication to reduce the thyroid levels in the body. It can be in a tablet form or a transdermal ointment placed on the inside of the ears of a cat. A restricted iodine diet called Y/D, made by Hill’s Pet Nutrition can be fed to hyperthyroid patients to treat the disease. Surgical thyroidectomy (removing the thyroid gland or glands) is possible. Lastly, radioactive iodine therapy can be used eliminate the diseased portion of the thyroid glands, leading to a cure of the condition.

The two most common treatments we see in practice at St. Francis are Methimazole and radioactive iodine therapy. Methimazole treatment is extremely common because the drug is relatively inexpensive and is a low stress method of treatment compared to surgery or the radioactive therapy. However, medicating a cat can be stressful for the owner AND the cat if the animal avoids trying to eat the pill in food or doesn’t like a pill shoved down its throat. The transdermal version of methimazole can be less stressful because it involves placing the ointment on the inside of the ears. It does increase the cost of the medication because it needs to be compounded into the transdermal form. Methimazole therapy is life-long, and may need to be adjusted over time to best treat the disease. Radioactive iodine therapy is considered the “gold standard” of treatment for hyperthyroidism because it is likely to cure the condition. An injection of radioactive iodine given to the patient destroys the diseased part of the thyroid glands, leading to remission. One drawback can be cost of treatment, costing $1500-3000, depending on the area of country you live in. The cat needs to stay in a special facility for a few days to be isolated and specially handled because of the radiation. Overall, this treatment is considered best for long-term control and because it is a cure, no additional treatment will likely be needed.

The other two therapies are uncommon. The surgery option can be a cure but some thyroid tissue can be missed and not excised or the parathyroid glands may be excised as well, leading to other potential complications post-surgery. It is also obviously invasive, costly, and will need to be treated medically prior to surgery.

The Y/D diet can be effective in reducing the thyroid hormone levels but the hardest part is getting the cat to eat the food and ONLY that food. In our experience, a lot of cats just do not want to eat that diet, rendering that therapy useless. Also, the owners forget that the diet must be exclusive, and feed other kinds of food along with the Y/D, rendering that therapy useless.

 

In summary, hyperthyroidism is one of the most common ailments we see in our feline patients. It is relatively easy to diagnose and treat, barring any related disorders or diseases. There are multiple options of therapy that can effective in relieving signs of this problem. If you suspect your middle-aged or geriatric cat has this condition, give us a call to schedule an appointment to have him or her evaluated. I hope everyone is having a great fall, and enjoying the cooler weather! Hasta la vista!

Dr. Jaime Kozelka
St. Francis Hospital for Animals