Dr. Katharine North: Recognizing and treating hyperthyroidism in cats


The older your beloved kitty becomes, the greater the chance disease is going to strike. Hyperthyroidism is one of the more commonly diagnosed diseases of senior cats. It can be found in males and females equally. It can be diagnosed between 4 and 20 years of age, but the vast majority are found in cats older than 8 years of age.

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Hyperthyroidism is caused by tumors in thyroid gland that overproduce thyroid hormone. Excess thyroid hormone essentially causes the body to run in high gear all of the time. Though tumors are a form of cancer, fewer than 2% of these growths cause problems outside of thyroid gland. This means that successful control of hyperthyroidism can improve quality and length of life for most of these cats.

Early in the disease, affected cats may show signs as subtle as small changes in drinking and urinating. Some might just start to be more vocal or more unsettled. As the disease continues, weight loss – despite a good or even increased appetite – may occur. Behaviour changes like increased crankiness, night waking, nervousness, and changes in activity are often seen. Owners may also see other symptoms such as vomiting with or without diarrhea, faster breathing or panting and seeking cool areas. Weakness and poor grooming causing scruffiness that may contribute to the old age cat look. These signs can come on so slowly that owners don't recognize them as symptoms of disease and think that they are just part of getting old.

Undiagnosed cats are at high risk of heart problems because the high-gear effect makes the heart beat at nearly twice its regular rate. They are also are more likely to have eye problems due to high blood pressure. The changes in blood flow also hide the signs of early kidney disease making it more difficult to diagnose and treat. Early detection of hyperthyroidism really minimizes the long term damage done to the body.

Senior screening with routine lab work that includes checking the thyroid is recommended from 7 years of age. This, in combination with senior wellness exams every 6 months, is the best way allow your veterinarian to diagnose hyperthyroidism and other senior diseases like kidney problems or diabetes.

As mentioned previously, early diagnosis and treatment of hyperthyroidism can improve quality and length of life. There are several treatment options available.

  • Radiation therapy to destroy the cancerous tissue is very effective. It requires a higher initial expense and a trip to a specialist – but often in the long term, the overall cost is relatively similar.

  • Surgery can be done on the thyroid gland, but can be technically challenging and has a higher cost.

  • Methimazole treatment can be given two or three times daily for life. This comes in pill and gel form. Side effects can occur. Each owner and cat team has a different level of tolerance with regular medicating. For some it is a treat and bonding time, but for others it can lead to hospital visits and replacing home furnishings! It is important for this medication to be regular and life-long.

  • Iodine-restricted diets can be fed. These must be the only source of food to work and should not be fed to unaffected cats. This can make this treatment too difficult to manage for most owners.

Consultation with your veterinarian will help decide which option might work for your situation.

Surgery and radiation rarely require continued monitoring of the thyroid, but both diet and Methimazole treatment need monitoring bloodwork on a regular basis. All treatments should have complete lab work repeated once the thyroid is stable to pick up other medical problems that may have been obscured.

Remember that senior cats don't have to be sick, old cats. They can be happy, thriving kitties late into their teens and twenties with regular care and early diagnosis of manageable problems like hyperthyroidism. Senior wellness exams and screening are fundamental to a long healthy life.

Dr. Katharine North (née Moody) has been a resident and active participant in the Fort St. John community since her family immigrated to Canada from the United Kingdom as a child. Her interest in medicine and animals led her back to the University of Liverpool in the U.K. to complete her Bachelor of Veterinary Science in 2000.

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