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In cats, hyperthyroidism results from functional thyroid adenomatous hyperplasia (growth of the glandular cells) or adenoma (a benign tumor). Rarely, a cancerous tumor (adenocarcinoma) causes feline hyperthyroidism. One or both lobes of the thyroid gland are involved (70 percent of cases involve both thyroid glands). Most cats with hyperthyroidism are ten years of age or older.

The most common clinical signs include hyperactivity, weight loss, increased appetite, vomiting, or diarrhea. In some cases (apathetic hyperthyroidism, which occurs in approximately five percent of cases), the cat does not experience these classic signs. Instead, the cat may act more lethargic, eat less, and generally act depressed or weak.

Diagnosis is made by finding elevated thyroid hormone levels on a blood profile. Other common geriatric diseases whose clinical signs mimic hyperthyroidism, such as kidney disease and diabetes, should be screened for as well. Secondary problems such as mild liver or heart disease usually resolve when the underlying hyperthyroidism is treated. Because older cats can also have kidney disease that may worsen if the hyperthyroidism is treated, cats with hyperthyroidism must be carefully screened for kidney disease prior to treatment of hyperthyroidism.

Principal Natural Treatments
Glandular Therapy—is recommended for cats. It uses whole animal tissues or extracts of the thyroid gland. Current research supports this concept that the glandular supplements have specific activity and contain active substances that can exert physiologic effects.

While skeptics question the ability of the digestive tract to absorb the large protein macromolecules found in glandular extracts, evidence exists this is possible. Therefore, these glandular macromolecules can be absorbed from the digestive tract into the circulatory system and may exert their biologic effects on their target tissues.

Several studies show radiolabeled cells, when injected into the body, accumulate in their target tissues. The accumulation is more rapid by traumatized body organs or glands than healthy tissues, which may indicate an increased requirement for those ingredients contained in the glandular supplements.

In addition to targeting specific damaged organs and glands, supplementation with glandular supplements may also provide specific nutrients to the pet. For example, glands contain hormones in addition to a number of other chemical constituents. These low doses of crude hormones are suitable for any pet needing hormone replacement, but especially for those pets with mild disease or those whom simply need gentle organ support.

Glandular supplements also function as a source of enzymes that may encourage the pet to produce hormones or help the pet maintain health or fight disease. Finally, glandular supplements are sources of active lipids and steroids that may be of benefit to pets. The dosage of glandular supplement varies with the product used.

Astragalus—is used to strengthen the immune system and acts as an antibacterial and anti-inflammatory herb. As a result, many doctors prescribe this herb for pets with various infections and for those with chronic illnesses, including cancer.

In cats, astragalus is often recommended for the treatment of hyperthyroidism. It can also be used to help the body recover from long-term steroid therapy and for pets with kidney disease, as this herb improves kidney circulation.

Astragalus membranaceous is safe, but other species of astragalus can be toxic. Do not use in pets with diseases resulting from an overactive immune system (autoimmune diseases).

Bugleweed—may be useful for cats with mild hyperthyroidism. Frequent doses of the herbal extracts must be given for several days before any result may be detected. Like digitalis, bugleweed can be helpful in heart conditions in which the heart's contractions should be strengthened and the rate (pulse) decreased.

Bugleweed can also act as a diuretic and remove excess fluid from the lungs, as might occur in congestive heart failure. It can be useful for pain relief and does not contain salicylic acid so it can be used safely in cats. Do not use in pregnant animals.

Lemon Balm—may be useful in cats to decrease thyroid output and possibly decrease blood pressure. As with the other herbs mentioned, controlled studies are hard to find, and herbs may not be helpful in cats with severe disease. The dosage of herbs varies with the product used.

Other Natural Treatments
Other therapies include homeopathies (homeopathic tyhyroidium), and whole food supplements. Use raw broccoli mixed in a homemade diet, as much as possible; or if the cat does not eat raw broccoli, use a whole food broccoli supplement such as Phytolin from Standard Process.

These can be used in conjunction with conventional therapies, as they are unlikely to be effective by themselves in most patients. The natural treatments are widely used with variable success but have not all been thoroughly investigated and proven at this time. As with any condition, the most healthful natural diet will improve the pet's overall health.

Safety Issues
Because vegetables such as broccoli and cabbage can depress thyroid hormone if eaten in large amounts, they should not be fed (or fed in only in small amounts) to dogs with hypothyroidism. The herbs mentioned above, while useful in treating cats with hyperthyroidism, should be avoided in dogs to prevent a worsening of clinical signs. Treatments to avoid in dogs include astragalus, bugleweed, and lemon balm.

Conventional Therapy
Three conventional therapies are recommended for cats with hyperthyroidism. Surgical removal of the thyroid gland can be performed. However, anesthesia is needed for this procedure; and while geriatric cats can be safely anesthetized, the other options for treatment usually do not require anesthesia and are usually preferred. Second, surgery, especially in severely hyperthyroid cats, is associated with significant morbidity (illness and trauma) and mortality, as well as the chance for postoperative calcium imbalances due to damage or inadvertent removal of the associated parathyroid glands.

Medical therapy, most commonly with methimazole (Tapazole), is another conventional option. The medicine is given for the life of the cat and is very successful in lowering levels of thyroid hormones. Rare side effects include lack of appetite, vomiting, lethargy, facial dermatitis, and low red cell, platelet, and white blood cell counts. Liver disease is also a possible side effect. Cats experiencing abnormal blood or liver profiles or facial dermatitis are at risk of future serious side effects and must have their medication stopped and another form of treatment instituted.

The third and most commonly used treatment for cats is radioactive iodine. While this sounds quite drastic, it may be the safest conventional treatment for hyperthyroid cats. Side effects are extremely rare, and most cats are completely cured after one treatment. Hypothyroidism, or low thyroid output, is a rare side effect of treatment that can easily be treated with thyroid replacement hormone if needed. Because radioactive iodine cures the hyperthyroid conditions, and because cats with underlying kidney disease could develop kidney failure when cured of their hyperthyroid conditions, it is essential that cats be screened for kidney disease prior to radioactive iodine treatment. The major concern among owners is that cats treated with radioactive iodine must be hospitalized for one week or more until they are no longer excreting radioactive iodine in their urine or feces.

A fourth, newer proposed treatment is injection of ethanol directly into the affected thyroid gland using ultrasound to guide the procedure (percutaneous ethanol ablation). Early studies appear positive, although some cases involved laryngeal paralysis secondary to leakage of ethanol from the thyroid gland and inflammation of the recurrent laryngeal nerve. More research is needed to determine whether percutaneous ethanol ablation will become a safe and effective therapy for treating feline hyperthyroidism.

Shawn Messonnier, DVM

As my thank you for reading my articles, enter code “drshawn” at my natural products web store,, to save 10% on all your future purchases!

Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!

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