Diagnosing Feline Hyperthyroidism

Feline hyperthyroidism is one of the most common endocrine diseases of the cat. Hyperthyroidism causes your cat's thyroid gland to produce too many of the hormones thyroxine (T4) and triiodothyronine (T3), which cause symptoms including weight loss, hyperactivity, and increased appetite. Luckily, hyperthyroidism is treatable.

Symptoms of Hyperthyroidism in Cats

Some of the most common symptoms of hyperthyroidism in cats include weight loss, increased appetite and hyperactivity. Increased water consumption and urination can also occur.

Gastrointestinal symptoms such as vomiting and diarrhea may occur. Cats may also display increased heart rate, arrhythmias and congestive heart failure. Cats with hyperthyroidism may develop a reversible form of heart disease. Most hyperthyroid cats will have an enlarged thyroid gland.

It's important not to confuse hyperthyroidism with hypothyroidism, in which your cat's thyroid gland fails to produce enough of the appropriate hormones rather than producing too many of them. Cat hypothyroidism causes different symptoms and requires different treatment.

Diagnosis of Feline Hyperthyroidism

Cat hyperthyroidism usually occurs in middle aged or geriatric cats. During the physical exam, your vet may notice heart murmurs, an accelerated heart rate, or a type of heart beat called a "gallop rhythm." Your vet may palpitate your cat's throat to feel for an enlarged thyroid gland.

Since the symptoms of feline hyperthyroidism could be similar to those of diabetes, cancer, liver disease or kidney disease, your vet will want to perform blood tests to check for elevated levels of thyroid hormones in your cat's blood. Your cat may have developed secondary illnesses, such as heart and liver disease, which will resolve themselves once the hyperthyroidism is treated.

Treating Feline Hyperthyroidism

There are three methods used to treat feline hyperthyroidism. Each has its own unique advantages and disadvantages, and your vet will help you decide which is best for you.

Radioactive iodine is the treatment of choice. It involves the use of irradiated iodine to destroy only the part of the thyroid gland that presents a problem. It has a very high success rate and does not require anesthesia. It does, however, require that your cat remain boarded at the treatment center for up to ten days to minimize radiation exposure to others.

Radioactive iodine therapy is done by a specialist and is available by referral. Your vet will want to treat your cat's hyperthyroidism with the drug Tapazole to make sure his kidney function will remain normal after the diseased part of the thyroid has been destroyed.

Tapazole, or methimazole, is the drug of choice for the treatment of feline hyperthyroidism. It doesn't cure the disease and so therefore must be a long-term treatment. Some cats may suffer from side effects including vomiting, lack of appetite, and depression. Tapazole is available in an oral or topical form.

The third option for the treatment of feline hyperthyroidism is surgical. A thyroidectomy can be very effective in the treatment of hyperthyroidism. It has a high cure rate, but requires anesthesia. A thryoidectomy may not be able to remove diseased thyroid tissue that has slipped down the throat into the chest.

Complications of thyroidectomy include improper calcium metabolism, hypothryoidism, and paralysis of the throat muscles.