Is Controlling Hyperthyroidism In Cats With Diet Possible?

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Our main issue is controlling hyperthyroidism in cats with diet. If your cat has hyperthyroidism, his thyroid gland produces too many hormones. However, abnormally high production of thyroid hormones can affect his health: weight loss, high blood pressure, or even hyperactivity are then on the program. To treat this disease, lifelong medical treatment is often administered. Surgery or radioactive iodine treatment can also be considered and thus allow complete recovery. However, they are rarely practiced. There remains one final solution: power management! Before moving on to controlling hyperthyroidism in cats with diet, let's get acquainted with hyperthyroidism in cats.

 controlling hyperthyroidism in cats with diet
A stranger in the house

Your cat, who was slowly aging, has become anxious, aggressive, and agitated: his character has changed. This mystery may be due to hyperthyroidism.

The thyroid is a gland located at the base of the neck, on either side of the trachea. It makes and releases hormones into the blood. These hormones act on the metabolism, that is, the general functioning of the body and the organs; in particular, they regulate body temperature and energy production.

In cats, the thyroid grows without knowing the cause. It's hyperthyroidism. The process involved is called adenomatous hyperplasia.

All adult cats (especially those over ten years old) can be affected, and the older the cat, the greater the risk.

Symptoms at first discreet

The signs that can alert you are:

Weight loss, especially if appetite increases

An unusual commotion

A change in behavior, anxiety, aggressiveness, excessive vocalizations

An increase in thirst and the amount of urine

Digestive disorders: vomiting, diarrhea/loose stools

An ugly coat

The appearance of a nodule in the neck (small mass)

Hyperthyroidism also causes an increased heart rate. Your veterinarian may also note the formation of a heart murmur (abnormal sounds during auscultation) and even high blood pressure due to the progression of the disease. Ultimately, if left untreated, the disease can be fatal.

 Different possible treatments for hyperthyroidism

If there is anything abnormal in a cat, it is worth seeking advice from a veterinarian. The latter will carefully examine your companion and look for, for example, a nodule in the neck and abnormal sounds on auscultation.

Then, he must take several blood tests to establish the diagnosis and assess the disease's consequences on the kidneys, in particular. Finally, he will discuss with you the different possible treatments.

The first stage of treatment is simple tablets. First, the veterinarian will explain how to give them to your cat. Then, he will establish a monitoring program to avoid side effects and choose the most suitable dose.

A simple diet can help control the disease. First, the cat must never go out because it must not receive any other food. This iodine-free diet prevents the thyroid from making hormones that make the cat sick. It is helpful for apartment cats that live alone.

Then, if your cat's kidneys are working well, the veterinarian may suggest that you have a scan done. Scintigraphy is an imaging method. It consists in detecting the radioactive elements injected into the animal and fixed by the abnormal tissues of its thyroid. It can be performed in some veterinary centers. The goal is to locate diseased areas that can be surgically removed. This surgical treatment is increasingly being replaced by a technique called iodine therapy. It uses radioactive iodine. Iodine destroys diseased thyroid tissue but spares healthy tissue. Unfortunately, this treatment is only carried out in a few reference centers. In addition, it requires hospitalization until the patient no longer represents a risk of radioactivity for the humans with whom he lives. This method achieves healing in most cases, but it is not always possible to implement.

Cat hyperthyroidism is a common disease in adult and aging cats. Therefore, consult a veterinarian if your cat is losing weight or has doubts. Similarly, a control can be carried out during the annual vaccination visit. Thanks to the treatments, hyperthyroid cats regain a good quality of life.                                     

controlling hyperthyroidism in cats with diet
Controlling Hyperthyroidism In Cats With Diet 

Good to know about controlling hyperthyroidism in cats with diet: before changing your cat's diet with hyperthyroidism, veterinary advice is essential!

A diet for hyperthyroidism in cats has recently been developed. Unfortunately, this iodine-depleted diet is available by prescription only.

Indeed, iodine intake is necessary for the production of thyroid hormones. Therefore, reducing iodine levels in food also limits the amount of thyroid hormone produced by the animal.

Generally, the cat's body begins to decrease its production of thyroid hormones from the third week of this diet. And it was only after a few months that production returned to normal.

Feed him exclusively foods without iodine

If you're starting to feed your hairball an iodine-free diet, you must give it only that. Indeed, if you were to feed it with standard cat food, treats, or table scraps, the diet would not be effective. Even in small quantities!

Make sure he can't hunt.

If your cat hunts and eats prey, controlling hyperthyroidism in cats with a diet is not an option. Indeed, your feline would also increase its iodine level in its body. All the efforts made before would then be for naught.

Choose canned food

Since your cat is producing too much thyroid hormone, he may tend to drink and urinate more often.

In this case, do not hesitate to favor canned wet food (pâtés). Indeed, the latter has a higher water content than dry foods (kibbles). Thus, your feline may produce less urine.

Choose protein-rich foods

One of the most common symptoms of hyperthyroidism in cats is an increased appetite accompanied by weight loss. This is because, for a good reason, hyperthyroidism accelerates the metabolism; the animal then burns its calories even before its body can absorb them and transform them into energy.

If your cat has lost a lot of weight and a large part of its muscle mass, it is, therefore, essential to growing. To do this, remember to choose foods rich in protein. You must be careful that the proteins are of high quality!

controlling hyperthyroidism in cats with diet
Hyperthyroidism Detailed Information

Hyperthyroidism (overactive thyroid gland) is a common disorder in older cats. It is caused by an increase in the production of thyroid hormones from the neck. The clinical signs associated with hyperthyroidism can be dramatic, and cats can become very ill. However, cats can fully recover in most cases.

Thyroid hormones play an essential role as an index of control of metabolic processes and the general activity level. This is why cats with hyperthyroidism tend to burn energy very quickly, and it is typical to observe weight loss despite the increased appetite and food intake.

Most cases, increased thyroid hormone production is due to benign (noncancerous) changes. Both thyroid glands are affected, although sometimes, one gland is more affected than the other. In addition, the affected thyroid tissue increases in size, but the underlying cause of this process is unknown.

Cats typically respond exceptionally well to treatment; if the disease is recognized early and treated correctly, the cat's prognosis will be excellent.

A malignant (cancerous) tumor known as adenocarcinoma may be the underlying cause of hyperthyroidism. Fortunately, this is rare and is only the cause of 1-2% of cases of hyperthyroidism. However, when an adenocarcinoma is present, treatment is much more complicated.

Common Clinical Signs

Hyperthyroidism is observed in most middle-aged cats, and it is rare to observe it in cats under seven years of age. Male or female cats are affected with the same frequency, and no studies show a greater predisposition to suffering from hyperthyroidism by breed. Of course, some evidence indicates that it is less common in Siamese cats.

Cats affected by hyperthyroidism usually show a wide range of clinical signs, which are very mild at first, but later become more severe as the disease progresses. Also, as this disease occurs primarily in older cats, some affected cats have comorbidities that complicate and even mask some clinical signs.

The classic signs of hyperthyroidism are weight loss, despite increased appetite (polyphagia), increased thirst (polydipsia), irritability, restlessness, and even hyperactivity. Many affected cats have tachycardia (a high rate of beats per minute) and unkempt hair. Diarrhea and/or vomiting are also can often appear. Some affected cats are markedly intolerant to heat and seek warm places to lie down, and some (especially advanced cases) may pant when stressed. Many hyperthyroid cats may show some degree of polyphagia (excessive appetite) and restlessness. Still, some advanced topics may show generalized weakness, lethargy, and loss of appetite, and the signs are less characteristic.

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Secondary complications

Thyroid hormones affect virtually every organ in the body, so it is not surprising that this disease can cause side effects that require additional research and treatment.

The effect of thyroid hormones on the heart consists of stimulating the heart rate (increased number of beats per minute) and a more muscular contraction of the heart muscle. As the disease progresses, the muscle of the heart's most central chamber (left ventricle) enlarges and thickens – known as left ventricular hypertrophy. If these changes are not treated and controlled, they can cause compromises in the normal function of the heart and can even result in heart failure. In some cats with hyperthyroidism, additional treatment will be necessary to control the side effects of hyperthyroidism on the heart. However, once the underlying hyperthyroidism has been controlled, the cardiac changes usually improve and even resolve completely.

Hypertension (increased blood pressure) is another potential complication and can cause additional damage to various organs, including the eyes, kidneys, heart, and brain. If hypertension is found in conjunction with hyperthyroidism, medications to control blood pressure will be necessary to reduce damage to other organs. However, as in the case of heart disease, hypertension may resolve after successful treatment of hyperthyroidism, and therefore, lifelong therapy may not be necessary.

Kidney disease (chronic kidney failure) is not caused by a direct effect of hyperthyroidism, but the two diseases often occur together because both are common in older cats. Great care must be taken if both disorders are concomitant since hyperthyroidism tends to increase blood flow to the kidneys, sometimes improving their function. Thus, blood tests to monitor kidney function in a hyperthyroid cat may show mild or regular changes, but more severe kidney failure may be masked by hyperthyroidism. For this reason, regardless of the treatment chosen for long-term management of hyperthyroidism (see below), it is usual to recommend starting medical treatment (pills) and monitoring response with various blood pressure measurements and urinalysis. To assess thyroid and renal function. Occasionally, successful treatment of thyroid values ​​leads to a dramatic decline in kidney function. If this is detected, it would be necessary to reduce the dose of antithyroid medication, even if the hyperthyroidism is not entirely controlled, to prevent the renal function from being too compromised.

controlling hyperthyroidism in cats with diet
Reaching The Diagnosis

If you or your veterinarian suspect that your cat may have hyperthyroidism, a thorough physical exam and some blood tests should be performed to confirm the diagnosis. On examination, one or both thyroid glands can be palpated as a small, firm mass located in the neck (usually the size of a pea or bean in hyperthyroid cats). However, some cats do not show this enlargement, and this may be because the hyperactive tissue is in an ectopic (unusual site) location, usually in the thoracic cavity.

The diagnosis is confirmed after analysis of thyroid hormones. All that is required to diagnose this disease is a blood test that determines the concentration of thyroxine (T4), and it is typically elevated in positive clinical cases. However, other laboratory tests may be abnormal; liver enzymes are elevated secondary to hyperthyroidism. A routine blood and urine check is also required to rule out other concurrent diseases (such as kidney failure). If possible, blood pressure should be checked in hyperthyroid cats. If a secondary cardiac problem is suspected, an electrocardiogram (ECG - electrical tracing of heart activity) and an x-ray of the thoracic (chest) cavity should be performed. Or cardiac ultrasound that can help with the diagnosis.

In rare cases, we may have an extreme suspicion that a cat is hyperthyroid based on clinical signs, but the blood test will reveal a thyroid hormone concentration within the normal range. There are several potential reasons why this happens, and usually, when repeating the test, the hormone values ​​are elevated.


This technique is available in some specialized centers and can help investigate some hyperthyroid cats. It can be used both for diagnosis and to determine the exact location of abnormal tissue. This can be particularly helpful when surgery is being considered, but an enlarged thyroid gland is not palpable on clinical examination. This technique injects a minimal dose of a radioactive substance (Technetium) intravenously. Technetium is selectively taken up by abnormal thyroid tissue and will be detected by a special camera (gamma camera). It is a simple, safe, and easy procedure that can be recommended in some situations.


There are three possible options for the treatment of hyperthyroidism, and each one of them has advantages and disadvantages;

Medical treatment

Antithyroid drugs are available in pill form. They work by reducing the production and release of thyroid hormone from the thyroid gland. This does not cause a cure for the disease but allows short- or long-term control of hyperthyroidism. Methimazole (its trade name is Felimazole) is given at a starting dose of 2.5 mg twice daily. Thyroid hormone concentrations typically decline within a 3-week range. For long-term treatment, the amount of Felimazol will be adjusted according to the evolution of the patient. To maintain control of hyperthyroidism, give Felimazole daily for the rest of the animal's life. Felimazole is the only veterinary licensed treatment for feline hyperthyroidism.

For most cats, methimazole (or carbimazole, a drug metabolized to methimazole ) is a safe and effective treatment for hyperthyroidism. Side effects are rare; if they do occur, they are mild and reversible. Loss of appetite, vomiting, and lethargy are possible side effects that often resolve within the first few weeks of treatment by temporarily reducing the treatment dose and taking the amount with food. More severe problems are rare, including reduced white blood cells, decreasing platelets (which help the blood clot), liver disorders, or skin irritation. Still, if they do occur, alternative treatment should be used.

Medical treatment of hyperthyroidism is readily available and inexpensive, but it is not curative. Lifelong treatment is required, usually a twice-daily oral dose, which can be challenging to adhere to for some owners (and some cats). Blood tests should be performed periodically during treatment to assess the effectiveness of therapy, to assess liver function (see above), and to look for possible side effects.

Surgical Thyroidectomy

Surgical removal of affected thyroid tissue (thyroidectomy) can produce a permanent cure and is the standard treatment for many hyperthyroid cats. It is generally a successful procedure and is likely to have a long-term therapy in most cats. However, after successful surgery, symptoms of hyperthyroidism may occasionally return.

To reduce anesthetic and surgical risk, it is recommended that all hyperthyroid patients be first stabilized with antithyroid drugs 3 to 4 weeks before surgery unless there is a significant contraindication to medical treatment. Any previous cardiac abnormality should also be treated if deemed necessary. Surgical skill and experience in this technique are essential for the surgery to succeed and avoid post-surgical complications. The most significant risk associated with surgery is possible accidental damage to the parathyroid glands—they are small glands that lie very close to or inside the thyroid glands and play a crucial role in maintaining stable calcium levels in the blood. If these glands are damaged, a sudden drop in blood calcium concentrations (hypocalcemia) can occur, putting the patient's life at risk. It is more likely to happen when both thyroid glands are removed simultaneously, as this can damage both parathyroid glands simultaneously. To minimize the risk of this complication in cats requiring removal of both glands, it would be appropriate to perform the surgery in two stages, removing the most affected gland first and waiting 6-8 weeks before releasing the second thyroid gland to allow recovery in the production of parathyroid hormone.

It is usually recommended that cats remain hospitalized for a few days after surgery to monitor blood calcium concentrations if necessary. Clinical signs of decreased blood calcium concentration include muscle tremors and weakness, rapidly progressing to explosive attacks. Treatment consists of oral and injected calcium supplementation. Additional treatment with vitamin D3 is also recommended to allow the calcium given by mouth to be absorbed effectively by the body. Once stabilized, treatment can be continued at home. In most cases, damage to the thyroid glands is reversible, and treatment is only needed for a few days or weeks.

Radioactive iodine therapy

Radioactive iodine (I131) can also be used to provide an effective and safe cure for hyperthyroidism. As with thyroidectomy, it has the advantage that, in most cases, it is a curative treatment and does not require maintenance with drugs.

Radioactive iodine is given as a subcutaneous injection. The iodine is taken up by active (abnormal thyroid tissue) but not by other body tissues. Radiation destroys abnormal thyroid tissue but does not damage surrounding tissue or parathyroid glands.

The advantages of radioactive iodine treatment are that it is curative, has no significant side effects, does not require general anesthesia, and treats all affected thyroid tissue regardless of location. However, it requires the handling and injection of radioactive material. This does not pose any risk to the patient, but people who come into direct contact with the cat must take preventive measures. For this reason, this treatment can only be performed by specially licensed facilities, and the treated cat must remain hospitalized until the radioactivity has dropped to acceptable levels. Usually, the cat must stay hospitalized for between 3 and 6 weeks (depending on the institution) once the treatment has been carried out. In most cats, thyroid hormone levels have returned to normal within three weeks, although sometimes it takes a little longer.

A single injection of radioactive iodine is curative in 95% of cases, and in those few hyperthyroid cats where the disease persists, a second treatment can be performed. Occasionally, after injection with radioactive iodine, there is a reduction in thyroid hormone levels below normal (hypothyroidism). Therefore, if accompanied by clinical symptoms (lethargy, obesity, poor appearance of the hair), it is necessary to administer a thyroid hormone supplement. (using tablets).

Treatment of thyroid carcinoma

On those rare occasions when hyperthyroidism is due to a thyroid adenocarcinoma (a malignant tumor), treatment is more complex, and the prognosis should be guarded. Some cases can be successfully treated with very high doses of radioactive iodine; others require conventional radiotherapy treatment.

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