Mary Allen
If your older cat is becoming restless or even aggressive, has excessive shedding, and is losing weight, it could be due to the thyroid gland. An overactive thyroid is the most common hormonal (endocrine) disease in cats and mostly affects older cats from the age of 8 years, but younger animals can also become ill.
The thyroid gland is located in the neck below the larynx and our domestic mammals are divided into two parts to the right and left of the trachea. The iodine-containing thyroid hormones T3 and T4 that it produces play an important role in energy metabolism and the growth of individual cells and the entire organism. They increase heart rate and blood pressure as well as body temperature, sweat production, intestinal motility, and the excitability of nerve cells. That is why the thyroid is often referred to as the body’s power plant.
If thyroid cells are destroyed and too few hormones are produced as a result, the result is hypothyroidism, or “hypothyroidism”. If, on the other hand, too many hormones are released (e.g. due to the influence of a thyroid tumor), this is referred to as an overactive condition, “hyperthyroidism”.
Note: Cats usually get an overactive thyroid gland while dogs tend to suffer from an underactive thyroid gland!
What Causes Hyperthyroidism in Cats?
In about 98% of cases, benign growths of thyroid tissue are the cause of hyperthyroidism in cats. This is often a so-called “adenomatous – multimodular hyperplasia”, in which tiny nodules develop in both thyroid lobes so that the thyroid gland enlarges overall. Somewhat less frequently, the proliferation occurs in the form of unilateral benign tumors (thyroid adenomas). Cats have a malignant tumor Enlargement of the thyroid gland leads to increased production of thyroid hormones.
What triggers these adenomas has not yet been fully elucidated. Nutrition and environmental influences, but also genetic factors could have an influence. According to studies, feeding commercial cat food is a risk factor for the development of the disease, which is attributed to the high content of thyroid-enhancing substances such as soy isoflavones or phthalates. In addition, environmental factors such as the use of certain cat litter may also be involved in the development of the disease. Flame retardant chemicals such as diphenyl ether in home textiles, carpets, and furniture are also traded as suspects. Although the use of diphenyl ether was banned in the EU some time ago, there are certainly still plenty of home furnishings containing the substance.
What are the Symptoms of Cats With an Overactive Thyroid?
The first signs are often not perceived by cat owners as an illness, but rather as a sign of health. The increasing activity of the old cat, combined with the increased appetite, is reminiscent of the young, growing cat. Often the cat is only presented to the veterinarian when it loses body weight due to increased appetite and food consumption and other signs such as increased thirst (polydipsia) and increased urination (polyuria). Increased hair loss is also one of the non-specific symptoms and is often dismissed as a change of coat.
Typical symptoms of an overactive thyroid in cats are:
- restlessness
- hyperactivity
- Increased heart rate and high blood pressure
- Significantly increased appetite
- Weight loss to extreme emaciation
The overproduction of thyroid hormones T3 (= triiodothyronine) and T4 (= thyroxine) and thus their increased release into the blood leads to an increase in the metabolism in every single body cell of the cat. This increases the energy consumption of each cell, which in turn means that the cat with hyperthyroidism has to consume significantly more food too, to be able to provide enough energy. As the disease progresses, it becomes increasingly difficult for the cat to meet its energy needs through food intake. This is how weight loss eventually occurs. The cat’s emaciation despite a good appetite is the most obvious sign of an overactive thyroid.
Other common symptoms:
- great thirst
- frequent urination
- coat changes such as hair loss, bald patches and a lackluster, dull coat
- vomit
- diarrhea
- aggressiveness
- excessive or decreased grooming habits
- weakness and lethargy
- damage to the kidneys
- damage to the eyes
- damage to the heart
- up to an advanced stage of loss of appetite
How Does the Vet Diagnose Hyperthyroidism?
In most cases, the vet can palpate an enlarged thyroid gland on the cat’s neck. A healthy thyroid gland is usually not palpable in a cat.
To get a reliable diagnosis, the veterinarian should carry out a blood test, because in almost all cats with an overactive thyroid gland an excessively high concentration of the thyroid hormone T4 (thyroxine) can be detected in the blood serum. In some cases, the diagnosis is more difficult because the T4 value is only slightly elevated or is even within the normal range. If all other symptoms nevertheless indicate hyperthyroidism, either the T4 determination can be repeated after some time or free T4 (fT4) and TSH in the blood serum can be determined.
Due to the often existing concomitant diseases, it also makes sense to do a complete blood count and a serum profile, for example, to check the liver and kidney function and also the heart. If there is a suspicion that other organs have also been affected, an X-ray may be necessary, or an ultrasound may be done to assess the organs in the abdomen.
What are the Options for Treating an Overactive Thyroid in Cats?
An overactive thyroid is usually treatable. However, if the condition goes undetected and untreated, the cat’s condition will worsen.
The most common therapy for hyperthyroidism consists of the lifelong administration of antithyroid drugs. These are drugs that disrupt the formation of T4 and T3 by blocking the incorporation of iodine. They only suppress the disease and when the medication is stopped, previously existing symptoms reappear. Antithyroid drugs for cats are available in the form of tablets or an ointment that can be applied to the pinna and massaged into it. To avoid initial side effects or negative effects on the kidneys, therapy is often started with a low dosage. If the blood and urine values are okay, the dose is gradually increased after two to three weeks.
In certain cases, the thyroid can also be surgically removed. Surgical removal of the thyroid makes sense, for example, in cats with a malignant thyroid tumor. However, only as long as no metastases have formed. The procedure should be performed in a specialized veterinary clinic and the cat should be monitored in the clinic for some time afterward, as various complications can occur. The most common complication is a (usually temporary) life-threatening calcium deficiency that arises because the parathyroid glands were removed (only in the case of large thyroid tumors) or are still recovering from the procedure. Do both thyroid lobes need to be removed?
Another option is radioiodine therapy. Here, radioactive iodine is administered to the cat. This destroys the thyroid tissue. Disadvantage: the cat has to be kept isolated in a special room for a while because it “radiates radioactively”. Excrement must be disposed of as hazardous waste. Only trained and protected personnel are allowed to take care of the animals. For cats with metastatic malignant tumors, which are very rare, radioiodine therapy is the only chance of surviving the disease.
What Do I Have to Consider During Drug Treatment with Thyroid Hormones?
- If possible, give the thyroid pills at the same time each day.
- Give the pill either always with food or always without, not even like that.
- If you forget a pill, it’s usually not a problem. Continue the treatment as normal the next day. However, if a blood test is due, the veterinarian must be informed that a tablet has been missed. The examination date should possibly be postponed.
- Note whether the cat is completely symptom-free, or whether symptoms of an overactive thyroid may reappear after some time. Then the thyroid values should be checked again and the medication dose adjusted if necessary.
- If your cat shows symptoms of hypothyroidism, such as fatigue, loss of appetite, excessive weight gain, or hair loss, the dose of medication is probably too high. In this case, take your cat back to your veterinarian.
Rarely, do thyroid medications can cause side effects such as loss of appetite or vomiting. They usually only appear briefly at the beginning of treatment and are harmless. However, if the side effects persist, the dosage may need to be adjusted or the drug stopped. Then make an appointment with your veterinarian.
Supportive Nutrition for Hyperthyroidism
In the meantime, the iodine-free feed has been developed that works in theory. In practice, however, it becomes more difficult because the cat may not be given any other food until the end of its life. Thus, iodine-free feed is hardly an option for people with hyperthyroidism, especially for outdoor cats who catch prey and thus absorb iodine.
When choosing food, you should make sure that no meat from the gullet, stick meat, or poultry necks is used. Because these can contain thyroid tissue and make the therapy more difficult. You should also pay attention to products with a lower iodine content when it comes to dietary supplements.
Oftentimes, cats with an overactive thyroid become picky about what they eat. Good, healthy food, if possible wet food, contributes a lot to a good quality of life.
Can Naturopathic Methods Support Your Cat?
Complementary methods such as phytotherapy and homeopathy help to increase your cat’s well-being and alleviate the symptoms and side effects. They can always be used to supplement and support conventional medicine, but usually not as the sole therapy.
Complications & Prognosis in Hyperthyroidism
It is not uncommon for hyperthyroidism to mask chronic renal insufficiency. Cats with an overactive thyroid will drink more, which benefits the kidneys. If the cat is now treated, the amount it drinks is also reduced, which makes renal insufficiency visible. Therefore, the kidneys should also be checked during a follow-up check, even if they did not show any abnormalities in the first blood count.
Another complication is blindness. Hyperthyroidism and renal insufficiency can lead to high blood pressure. If the cat suddenly shows wide, open pupils or runs into objects, a veterinarian should be consulted as soon as possible.
The heart can also be affected by the overactive thyroid gland. In this case, heart disease must be treated. But if it was triggered by the overactive thyroid, there is certainly hope that the heart will return to normal with the treatment of the thyroid and the heart drug can be discontinued.
Conclusion
The quality of life of your cat, which has been correctly adjusted with medication, is very good. Regular blood tests and an adapted diet are necessary and important. You should also keep an eye on your cat’s behavior. So your cat can lead a largely normal cat life even with an overactive thyroid.