Hyperthyroidism in cats

The following information does not intend to replace regular visits to the vet. If you think that your cat may have hyperthyroidism, immediately consult a veterinarian. Remember, do not give the animal any medications, without consulting with a veterinarian.

What is hyperthyroidism?

Hyperthyroidism is the most common disease of the gland in cats. Most often it is caused by an excessive concentration of circulating thyroxine, the thyroid hormone, better known as T4, in the bloodstream.

What are the symptoms of hyperthyroidism?

Weight loss and increased appetite are among the most common clinical signs of this condition. Weight loss is observed in 95 - 98% of cases of hyperthyroidism in cats, and a strong appetite - in 67 - 81% of cases. Also reported was excessive thirst, increased urination, hyperactivity, slovenly appearance, dyspnea, diarrhea and increased hair loss. Vomiting is observed in about 50% of the affected cats. Clinical symptoms are the result of exposure to elevated T4 levels on various organ systems.

What breeds of cats (cats of what age) are prone to hyperthyroidism?

Hyperthyroidism can occur in any breed of cats, males and females, but it arises almost exclusively in older animals. Less than 6% of cases occur in cats younger than 10 years. The median age at onset of the disease is 12 to 13 years.

How is hyperthyroidism diagnosed?

Since some common diseases of older cats, such as diabetes, inflammatory bowel disease, intestinal cancer and chronic renal failure, have some common clinical symptoms with hyperthyroidism, a number of studies are needed. Clinical, biochemical blood analysis and clinical urinalysis alone do not diagnose hyperthyroidism, but can definitely exclude diabetes and kidney failure. Cats suffering from hyperthyroidism may have normal results of a clinical analysis of blood and urine, but a biochemical blood test often shows an elevated level of certain liver enzymes.

In the overwhelming majority of cases, the final diagnosis of hyperthyroidism is based on a simple blood test that shows an elevated level of T4 in the bloodstream. Unfortunately, in 2-10% of cats suffering from hyperthyroidism, the normal level of T4. One possible explanation is that in mild cases, the T4 level can go out and return to normal. Another explanation is that the concomitant disease holds back the T4 level elevation, lowering it to the normal level or the upper limit of the norm, which causes the veterinarian to erroneously think that the cat's thyroid status is normal. Since these are elderly cats, concomitant diseases occur quite often, and it can be difficult to diagnose hyperthyroidism in such cats.

How is hyperthyroidism treated?

There are several options for treating hyperthyroidism, each of them has its own advantages and disadvantages.

• Oral administration of an antithyroid agent. Metimazol (trade name Tarazol TM) has long been the basis of drug therapy for hyperthyroidism in cats. It is very effective in treating this condition, often there is a result in 2 - 3 weeks. Unfortunately, 15 to 20% of cats have side effects, such as loss of appetite, vomiting, drowsiness, blood clotting disorders, jaundice, pruritus of the head and muzzle, and sometimes changes in blood cells. Most side effects are mild and eventually they go away, although sometimes the drug can be canceled. It takes a lifetime daily medication, which is a disadvantage for the owners, whose cats resist taking the pills. A clinical blood test and T4 analysis should be repeated regularly for the rest of the cat's life.
• Surgical removal of the thyroid gland. Hyperthyroidism is usually caused by a benign tumor called adenoma of the thyroid gland and captures one or more of both of the thyroid glands. Fortunately, most cats suffering from hyperthyroidism have benign, well-encapsulated tumors that are easily removed. Surgery usually leads to recovery, but anesthesia may be undesirable for elderly patients, as their diseases could affect the heart and other organs. Although the operation may seem expensive, it is often less expensive than the years of oral medication and regular repeated blood tests.
• Therapy with radioactive iodine. This is the best and most difficult treatment option. Radioactive iodine, which is injected (usually under the skin), is concentrated in the thyroid gland, where it radiates and destroys hyperfunctioning tissue. Anesthesia or surgery is not required, and usually only one course of treatment is needed to achieve recovery. Earlier, treatment with radioactive iodine was carried out only in specialized licensed institutions, but now there are many private medical institutions. Hospitalization can be prolonged. Depending on local or state regulations, cats may need to stay in the health facility for 10 to 14 days until the level of radioactivity in urine and feces drops to an acceptable level. Also, therapy with radioactive iodine is expensive. The price has decreased from about $ 1,200 to $ 500- $ 800, but for most owners of cats it still remains prohibitively high.

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