Hyperthyroidism is a disease of the endocrine system, affecting humans and other animal species. In general, endocrine disorders have been on the rise due to inferior diets, processed food, and chemicals in the environment. It is rare in dogs but is becoming more common in cats.
What is hyperthyroidism in cats?
Hyperthyroidism is defined as an overactive thyroid gland. Cats have two thyroid glands in the neck, one on each side of the trachea. Also called thyrotoxicosis, hyperthyroidism is caused by an increased production of thyroid hormones (known as T3 and T4) from an enlarged thyroid gland in a cat’s neck. In most cases, enlargement of thyroid glands is caused by a non-cancerous tumor called an adenoma. Only 1-2% of hyperthyroid cases in cats involve malignant (cancerous) thyroid gland tumors. Even so, many organs are affected by hyperthyroidism, especially the heart. Hyperthyroidism is a common disease in cats and mostly afflicts middle-aged and older cats. No individual breed is known to have a greater risk; however, certain breeds (Siamese, Burmese, Persian, Abyssinian, Tonkinese, and British shorthair) appear to have a decreased incidence compared to other breeds. Cats affected by hyperthyroidism have much higher metabolism than those with normal thyroid glands.
What causes hyperthyroidism in cats?
The reason why adenomas in the thyroid result in excessive production of thyroid hormones is not completely known. One theory is that there exists a link between elevated T3/T4 and exposure to the chemicals PBDEs (polybrominated diphenyl ethers), a chemical flame retardant, and BPA (bisphenol-A), a chemical used to coat the inside of pet food cans. The amount of iodine in cat foods may also play a role, as well as the addition of soy, which can disrupt thyroid function. The cause is likely a combination of genetic factors and environmental conditions.
What are the symptoms of hyperthyroidism in cats?
The signs of hyperthyroidism vary depending on the stage of the disease and how long the glands have been overactive. Early signs include:
- Increased appetite with weight loss
- Increased thirst and urination
- Increase in vocalization
- Palpable mass in the neck/enlarged thyroid gland
- A sudden increase in energy/hyperactivity
- Behavioral changes (more anxious/fractious/aggressive)
- Gastrointestinal signs such as vomiting and diarrhea
- Reduction in grooming activities/loss of coat condition
- Alopecia (hair loss)
- Racing heart rate
- Sleep disturbances
These symptoms will progress and become more profound. Over time, increased metabolism will lead to high blood pressure, heart disease, kidney disease, liver disease, respiratory issues, and skin disorders.
Late stages of the disease may result in additional symptoms:
- Seizures
- Lack of coordination
- Muscle tremors
- Muscle weakness and wastage
- Dilated pupils
- Blindness
- Heart arrhythmias and murmurs
How is feline hyperthyroidism diagnosed?
Your veterinarian will start with a full physical exam and a detailed clinical history. Be sure to tell your veterinarian of any symptoms you may be observing. That information will help your doctor determine which blood tests to perform. The first step is to run a blood test that measures the level of the thyroid hormone called thyroxine (TT4). When the TT4 test is above the high end of the normal range, your veterinarian may diagnose your cat with hyperthyroidism with no further testing. If the TT4 test shows a thyroxine level in the upper range of normal, a second test, called a “free T4” (free T4 by equilibrium dialysis) or a T3 suppression test is performed. If the results of these tests do not definitively diagnose hyperthyroidism, a thyroid scan (thyroid scintigraphy) can be performed. Once a diagnosis of hyperthyroidism is made, I recommend that all vaccinations be stopped.
How is hyperthyroidism treated?
There are four conventional treatment options for feline hyperthyroidism: medication, radioactive iodine therapy, surgery, and dietary therapy. Each option has its advantages and disadvantages. Treatment choice depends on the cat’s overall health, the parent’s ability and willingness to medicate the cat regularly, and financial considerations.
Medication: Anti-thyroid medications like methimazole act by reducing the production and release of thyroid hormone from the thyroid gland. These drugs are not a cure, but they can control the disease. Lifelong treatment will be required. Treatment usually involves a twice-daily oral dosage, which may be challenging for some owners to maintain. Antithyroid medications are also available in a gel that can be applied to the skin. These medications are readily available and inexpensive. However, there are side effects including vomiting, anorexia, fever, anemia, allergic dermatitis, lethargy, suppression of bone marrow with low red and white cell production, and liver failure. Your veterinarian will guide you to which medication, dosage, and form (pill or gel) is best for your kitty. Blood work will need to be run periodically during treatment to monitor the drug’s effectiveness, as well as kidney and liver function.
Radioactive Iodine Therapy: This therapy has become the treatment of choice for cats with hyperthyroidism. With this therapy, radioactive iodine is injected under the skin. The iodine, which is required by both T3 and T4, is taken up by the thyroid gland and the emitted radiation destroys the abnormal thyroid tissue without damaging the surrounding tissues or the parathyroid glands. The procedure most often cures hyperthyroidism, has no serious side effects, and does not require anesthesia. The procedure must be performed at a facility that is specially licensed to use radioisotopes. Cats remain hospitalized until the radiation level has fallen to acceptable limits. The cost of the procedure can run into the thousands of dollars; however, this option may prove better for the pet and the family if the medication expense and thyroid level monitoring is eliminated.
Surgery: Removal of the thyroid glands, called surgical thyroidectomy, is a relatively straightforward procedure that has a good success rate. This surgery should be performed by a highly skilled surgeon in a specialty center. The surgery is performed under general anesthesia, and there might be added risks if older cats have heart, kidney, or other problems that could cause complications. If the thyroid is removed entirely, the cat will need to take thyroid supplements for life.
Dietary Therapy: In conventional medicine terms, “dietary therapy” refers to feeding the cat a prescription diet with low levels of iodine. I do NOT recommend Hill’s Y/D food. This diet is severely deficient in iodine, resulting in decreased production of thyroid hormone. While the diet may diminish symptoms, it will not diminish the size of any tumors present. Furthermore, the whole body would be deprived of iodine, which may have unknown repercussions. In a household with multiple cats, feeding could get tricky as cats without hyperthyroidism disorder should not be eating this food. This is a controversial therapy because of these concerns, and research into this potential treatment is ongoing.
What alternative treatments are available for treating feline hyperthyroidism?
The hardest thing about using alternative treatments is getting them into the cat. However, alternative treatments have shown promise in treating hyperthyroidism without serious side effects. As cat owners already know, most cats do not enjoy being medicated. I am not a fan of the ingredients used to make products such as “Pill Pockets,” but they can be a lifesaver for medicating cats. Powders and liquids can be added to meals in most cases.
Food therapy: A high-quality, species-appropriate, high-moisture diet, whether raw, gently cooked, canned, or freed-dried raw, is essential. Select Yin-tonifying (cooling) meats such as rabbit, duck, grass-fed beef, liver, and clams. Foods high in vitamin A like carrots, kale, spinach, and barley grass can be added in small amounts if the cat will tolerate them. They can be served cooked or raw.
L-Carnitine is used in humans to reverse the signs of hyperthyroidism in and is effective in cats as well. The recommended starting dose is 250mg daily. L-carnitine also provides cardiac support. Taurine supplementation also supports heart function. Taurine can be found in high quantities in red meats, poultry, eggs, dairy products, and fish.
Liver support is essential because liver enzymes are commonly elevated with this disease. Milk thistle and SAM-e can detoxify and support the liver.
Herbal remedies can be used to balance thyroid function. Bugleweed and Melissa are herbs used together to decrease thyroid hormone levels. Hawthorn can help lower blood pressure and decrease the work of the heart.
Homeopathy: The homeopathic remedy, Nat Mur, is recommended by alternative practitioners for reducing thyroid hormone levels. In a clinical trial, Nat Mur 30C provided impressive results in treating hyperthyroid cats. The recommended dosage is 1 tablet every 12 hours, with effects assessed after 30 days.
Acupuncture can balance the immune system, lower blood pressure, and support the kidneys and liver.
While there are conventional treatments for this hyperthyroidism, natural treatments are also effective. A whole-food, species-appropriate diet boosts the immune system. Herbal supplementation can lower thyroid hormone levels without the side effects of conventional medication. Feed your cat with a bowl or platter that does not contain BPA. Be sure the furniture or toys your cat uses do not contain PBDEs. Hyperthyroidism is a serious disease, but it can be controlled with proper care.
