FELINE HYPERTHYROIDISM

Hyperthyroidism is a progressive disease. Symptoms, if untreated, will continue to worsen until the cat dies.

Clinical Signs:

• weight loss
• increased appetite
• accelerated heart rate (and arrhythmias/murmurs)
• poor hair coat
• hyperactivity (or lethargy)
• vomiting
• diarrhea
• excessive thirst
• excessive urination
• increased vocalization
• increased respiratory effort (or panting)
• behavioral changes

Diagnosis:

Treatment Options:

• Medication: The most common anti-thyroid drug used to control the signs of hyperthyroidism is methimazole. Methimazole will block the production of thyroid hormone by the thyroid gland. It will not destroy the tumor in the thyroid gland, and therefore will not cure the disease. However, it can effectively control the signs of hyperthyroidism when given daily. Since therapy requires giving your cat tablets every day, you must be able to successfully give your cat oral medication (either by pilling or mixing in food). Be aware that not all cats will take pills when mixed in food and they must receive the full amount every day diligently. If drug treatment is interrupted, even for a day or two, hormone levels will increase and signs will return. For cats that are difficult to medicate with pills, the methimazole can be specially compounded into either a flavored treat or a trans-dermal gel. The flavored treats work well for cats that are good treat eaters. The trans-dermal gel is a cream that is rubbed on the inside of the ear pinna and absorbs through the skin. While this is more expensive (roughly double the cost of the pills), it tends to be easier for those owners that can not give pills to their cats. Side effects of methimazole are uncommon. Most side effects occur within the first 3 months of therapy and include vomiting, decreased appetite, lethargy and allergic reactions involving intense facial itchiness. Other side effects involve blood cell abnormalities and worsening of pre-existing kidney or liver disease. Therefore, routine monitoring of blood work parameters is important throughout the rest of the cat's life especially just after starting the medication or making a dosage adjustment. The cost of therapy depends on your cat's dosage of medication, how many follow up blood work checks need to be done and whether any side effects occur.
• Surgery: Surgery can be performed to remove the overly active thyroid gland, thereby curing the hyperthyroid state. However, surgery does have many potential side effects. In addition to the risks of anesthesia, there is a possibility of removing too much of the surrounding tissue including the parathyroid gland. This can cause complications involving calcium balance which can be very serious. Also, surgery may fail to cure your cat and it may need to be repeated. Surgery is usually only performed for those cats that experience too many side effects with methimazole and radioiodine treatment is not available.
• Radiation Therapy: Radiation therapy can only be done at specific facilities that specialize in this form of treatment. An injection of Radioiodine (I-131) is given under the skin which selectively destroys the thyroid tumor. Radioiodine treatment can permanently cure up to 95% of all cats with just one injection. Your cat must have some blood tests and xrays done by our hospital prior to treatment (costing about $250-500 depending on what has already been done). The closest treatment facility (Radiocat) is in Middletown, CT and the cost is $1250. Your cat will need to stay at that facility for approximately 3-5 days until the radiation level has dropped enough for you to safely take your pet home. Side effects of treatment are uncommon. We can provide you with more detailed information upon request.

Monitoring:

Prognosis:

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