Feline Hyperthyroidism

HYPERTHYROIDISM IN CATS

Cats can live to a ripe old age. In our clinic, the oldest feline patient was 24 years old, and there are plenty in the 16-20 year-old age group.

Generally speaking, when cats reach old age they tend to be less heavy than when they were younger, just as people are in their 90's. Old cats become 'wasted'- there is less muscle and they are less strong. The bones of old cats are thinner, lighter and more fragile, thus your favourite puss is seen wobbling down the garden path, spending more time sitting in the sun and no longer leaping in the kitchen window. The cat is quite happy nevertheless, just unable to do the things he or she used to do, and perhaps feeling the cold a little more.

However some cats look old before their time. They lose condition and look skinny when they are only 12 or 13 years old. But they are also glutinous eaters and will demand attention every time you go near the fridge or pantry. Despite all this, they lose weight. There can be many reasons for this, such as poor digestion or problems with worms. If the cat also drinks a lot of water there may be kidney problems or sugar diabetes. Sadly in some cases there may be growths in the body.

Nowadays veterinarians have been finding that many of these cats have in fact developed an overactive thyroid gland. This disease is known as hyperthyroidism. Hyperthyroidism (an overactive thyroid gland) is very common in middle-aged and old cats. It is always a treatable disease. The thyroid glands are situated in the neck. One or both of these glands enlarge when diseased and sometimes become palpable (the vet can sometimes feel the enlarged thyroid gland, about the size of a small pea, beneath the skin of the cat 's neck). Over 98% of enlarged thyroid glands are benign(non-cancerous).Hyperthyroid cats may have the problem in both thyroid glands.

The thyroid gland is involved in regulating the cat's rate of metabolism.When overactive, the thyroid gland produces more thyroid hormone than usual, often 2-3 times as much. This hormone circulates in the bloodstream and causes an increase in the rate of metabolism. This usually becomes apparent in the patient as weight loss, sometimes increased activity and increased appetite, an increased heart rate and often a poor haircoat. Often the blood pressure is raised, sometimes leading to kidney problems and changes in the eyes. The heart is often affected and enlarges, leading to heart disease. Many of the changes are reversible with treatment of the underlying thyroid disease. Less common signs of hyperthyroidism include skin changes; drinking and urinating excessively; vomiting; diarrhoea; aggressive behaviour; lethargy; weakness; anorexia (decreased appetite).

When vets suspect thyroid problems, we diagnose the problem using a blood
test. Some cats with early thyroid disease have normal thyroid hormone levels in the blood; it is important that these cats are re-tested in 4-6 weeks, and sometimes a modified blood test is required.

When diagnosing thyroid disease, it is important that we make sure that the cat has no other problems which may make treatment difficult, unrewarding or dangerous. For example, many older cats have kidney or liver problems.Sometimes we may need to take an x-ray to identify enlargement of the heart or problems in the chest or abdomen. We also like to test a urine sample to help us rule out other problems.

Once we have a diagnosis of hyperthyroidism, there are three treatment options:

1)Injection with radioactive iodine.

This is a very effective, non-invasive treatment. It is the treatment of choice in both cats and human beings. It is a simple, single injection. Cats generally do really well after this treatment.
Because they excrete radioactive material in urine and faeces after this injection, the cats must be kept in a special facility for 7-10 days until no longer excreting dangerous levels of radioactivity. This procedure is only performed at licensed Clinics and costs about $650.

2)Administration of Neo-mercazole tablets to interfere with the production of thyroid hormone.

For cats that accept tablets readily (twice daily usually) this is an easy and effective form of treatment. Most cats will take these tablets readily if crushed and mixed with their food. Regular monitoring of blood thyroid levels (and kidney function) is important with this method of treatment. The tablets must be administered indefinitely. Stabilistion to normal thyroid hormone levels is usually achieved in two weeks. It has been widely used for years as a treatment for hyperthyroidism in cats and has few side effects. These pills can also be especialy formulated as a dermal gel and applied to the ear of the cat if the cat refuses pills in the food.

3)Surgical removal of the affected thyroid gland.

This method can be effective, especially with very enlarged glands, and means that the tablets only have to be given to achieve initial stabilisation (2-3 weeks). The surgery involves a general anaesthetic.Cost is usually about $750.00 including blood sampling and fluid therapy.

The best approach these days is to initially start these cats on the tablets and administer these for a month or so. If the cats do really well, it is advisable to then do the radioactive iodine treatment so that neither owner nor cat has to endure persistent tablet administration.

The price of the neomercazole tablets now means that the radioactive iodine treatment is becoming more cost effective. It is also the most convenient and easiest treatment for both cat and owner.

The good news is that the disease can be successfully treated in almost all cases.

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