If your adult cat suddenly begins to lose weight despite a voracious appetite, he may have a hormone problem, specifically the hormone produced by the thyroid gland. You should probably get your pet to a veterinarian to be checked for feline hyperthyroidism.

Feline hyperthyroidism has become a widely recognized disorder in cats. It is caused by an unregulated overproduction of thyroid hormone by the thyroid glands, which is usually related to a benign enlargement (growth or tumor) of one or both thyroid lobes. This enlargement of the thyroid gland(s) is referred to as thyroid adenoma or thyroid adenomatous goiter. It is unknown what causes the thyroid to become enlarged.

The thyroid gland consists of two flat lobes shaped like a butterfly and located on either side of the trachea, or windpipe, just below the voice box. These lobes are flattened and cannot be easily palpated. The thyroid gland acts as the thermostat for the metabolic rate of the body, controlling how fast or slow the body functions. Hyperthyroidism can have effects on multiple organ systems, since the increased thyroid hormone levels increase the cat’s metabolic rate.

Although this disease is usually diagnosed in older cats (at least 9 years of age), it has been diagnosed in cats as young as 6 years of age. There is no recognized breed or sex predilection for this disease.

What to Watch for

Weight loss in spite of an increased appetite

Restlessness

Increased activity levels or irritability

Diagnosis

Diagnosis can be made by a simple blood test that measures the level of the thyroid hormone (T4). Your veterinarian may also perform other diagnostic tests to exclude other diseases, including:

Complete medical history and physical examination

Complete blood count (CBC) and serum chemistry profile

Thoracic radiographs

A T3 suppression test in hard-to-diagnose cases

In some cases a radionuclide scan (used in diagnosis for whole body or individual organ scanning)

Treatment

Treatment is directed at controlling excessive secretion of thyroid hormones and can involve a variety of approaches depending on several factors. These include your cat’s overall health, availability of radioactive iodine therapy and cost considerations. There are three main methods of treatment:

Radioactive iodine therapy

Surgical removal of the abnormal thyroid lobes

Medical therapy with Tapazole® (methimazole) and beta-adrenergic blockers (such as atenolol) to reduce some of the symptoms of hyperthyroidism

Home Care

At home, be sure to administer any medications prescribed by your veterinarian. If your cat is taking Tapazole®, a potential adverse effect is loss of appetite, which may be related to liver complications.

Preventive Care

There is no prevention because the cause is not known. However, examination of the thyroid area should be a regular part of any veterinary examination in older cats. If weight loss occurs in your older cat, your veterinarian may recommend a thyroid blood test to screen for this condition.

To learn more about hyperthyroidism in cats, please click on Hyperthyroidism In-depth.