Home » other animals » Cat Hyperthyroidism: Recognizing and Treating Hyperthyreidism?

Cat Hyperthyroidism: Recognizing and Treating Hyperthyreidism?

Hyperthyroidism in a cat

Every living organism coming into the world is subject to an inexorable aging process and with each day of its life, whether it wants to or not, it is relentlessly nearing its biological end.

Of course, we do not think of ourselves in this decadent way on a daily basis, but nevertheless, the progressive processes related to the functioning and wear of organs and organs proceed constantly.

It is a natural course of things, although in fact everyone would like to be beautiful, young and healthy as long as possible, if not constantly.

While the aging process in humans takes place over a longer period of time and some symptoms are noticeable only after several decades, in our animals, due to the fact that they live shorter, it is much faster.

We must accept that even the most active and energetic dog and cat will someday experience old age and related geriatric diseases.

It is sometimes difficult to accept the fact that a 7-8 year old dog or cat is already included in the group of older animals and therefore requires more care on our part, more frequent examinations or check-ups at the veterinary office.

We should remember that any previously diagnosed disease creates a greater chance for full recovery or at least for a longer life comfort and its extension.

So what should you pay attention to when you own an older cat?

There are many diseases that can manifest in a senior.

Among them, the first place in terms of the frequency of endocrine diseases is hyperthyroidism, i.e hyperthyroidism.

I will try to introduce you to this disease in the following article.

At the same time, I would like to sensitize the owner of an older cat to certain symptoms and a quick visit to the veterinary office and possible medical intervention.

  • What is the thyroid gland and why is it so important
  • Cause of hyperthyroidism in a cat
  • Which cats are most at risk?
  • Signs of an overactive thyroid in a cat
  • Disease diagnosis
  • Treatment of hyperthyroidism in cats
    • Surgical removal of the thyroid gland
    • Drugs for hyperthyroidism in a cat
    • Radiotherapy
  • Diet of an overactive thyroid gland in a cat

What is the thyroid gland and why is it so important

Thyroid (glandula thyroidea) is a paired endocrine gland located near the larynx.

It produces hormones that are extremely important for the proper functioning of the body:

  • thyroxine (T4),
  • triiodothyronine (T3),
  • calcitonin.

There are vesicles in the parenchyma that produce these two hormones (T3 and T4) as well clear cells - cells C producing calcitonin and to a lesser extent serotonin and somatostatin.

From the point of view of hyperthyroidism, we will be interested in the hormones T3 and T4.

These hormones are derived from the amino acid tyrosine, which is the starting product for their production.

The entire process takes place inside the thyroid gland follicles, from which they are released into the bloodstream as needed.

Importantly, it is thyroxine, i.e. T4, that is present in the predominant amount (up to 99%) in a form bound to a transport protein as opposed to triiodothyronine, i.e. T3 loosely bound and therefore quickly and easily available, if necessary, to the body.

Hence, it is T3 that is considered to be a biologically active form, although in fact there is much less of it (the ratio of T4 to T3 is 50: 1) in the bloodstream.

Triiodothyronine it is also largely formed in the peripheral blood as a result of the process thyroxine deionization.

The small amount of thyroid hormones that are not bound to proteins and that circulate in the bloodstream is known as free thyroxine (fT4) or free triiodothyronine (fT3).

A specific property of the thyroid gland is its enormous storage capacity iodine and acting as a reservoir for the organism of this element.

This feature ensures the smooth functioning of the organ for many months, even in the absence of this micronutrient in the food.

By the way, it was used after the accident at the Chernobyl power plant, when children were given Lugol's solution containing iodine, in order to saturate the thyroid with this element, and not with its radioactive isotope.

Production in the thyroid gland is strictly regulated on the part of pituitary gland in turn producing the hormone TSH - thyrotropin, and she, in turn, depends on the hypothalamic hormone TRH, that is thyreoliberin and is based on the principle of negative feedback.

Thyroid hormones are extremely important for the body's metabolism because they affect all tissues and organs of the body, thus influencing almost every biochemical process.

They are extremely important in the development of the fetus, especially its muscular and nervous systems.

They regulate the metabolism of fats and carbohydrates, affect the work of the heart muscle (positive isotropic and chronotropic effects), and stimulate the process of hematopoiesis, i.e. erythropoiesis.

They also affect the smooth functioning of osteoclasts and osteoblasts, i.e. cells responsible for bone development and bone metabolism.

By interacting with the growth hormone, they are irreplaceable in the development of the body - both somatic and sexual.

Since we already know the role of hormones in the cat's system, we can move on to describing the pathological situation, when there are too many of these hormones.

Cause of hyperthyroidism in a cat

The main causes of hyperthyroidism in cats are benign neoplastic growths about this organ.

At the same time, we do not know the causes that cause them, but based on the high levels found antinuclear antibodies (ANA) we can suspect autoimmune basis of this disease.

Cancerous growths in cats are always hormonally active and cause the condition hyperthyroidism and its consequences.

In a few cases, not all 5%, the cause of hyperthyroidism may be malignant neoplasms of the thyroid gland, that is, hormonally active adenocarcinomas.

It is also worth mentioning the influence of nutrition on the development of thyroid neoplasms.

Cats living in iodine-poor areas are more likely to develop an enlarged thyroid gland and develop a cancerous process.

They develop adenocarcinomas more often due to chronic iodine deficiency, which takes place in areas where this element is leached from the soil as a result of, for example, more frequent floods.

Scientists suspect many more factors that may affect the development of the disease, although it has not been undeniably documented many times.

And so often there is a suspicion that the large impact of not leaving the house of cats and the life associated with it, i.e. eating ready-made canned food or using the litter box, as factors contributing to the development of hyperactivity.

The thyroid gland in cats is made up of two lobes, and hyperfunction affects either one or both of them.

As we can see in the case of hyperthyroidism, not everything is known yet and sometimes it is difficult to answer the question in a simple way:

what is the cause of the disease?

Which cats are most at risk?

Which cats are most at risk of having an overactive thyroid??

The disease is much more common in middle-aged cat or the elderly, that is over 8 years of age (other sources mention cats 12-13 years old).

So far, no racial or sexual predisposition has been found in the course of hyperthyroidism, although it is more common in Siamese or Himalayan cats compared to other cats.

There is also a suspicion that indoor cats that use a litter box outside of a litter box and are fed commercial food are more likely to develop this condition.

So we can clearly see that the disease does not lend itself to easy classification, and for now, we can only be sure that it mostly occurs in prime or elderly animals.

Signs of an overactive thyroid in a cat

The thyroid gland is an extremely important secretory gland that produces hormones, hence the symptoms of excess hormones must be serious and under no circumstances should they be underestimated by the cat's owner.

As a result of hyperactivity the metabolic rate increases, the consequence will be negative protein balance (in the body, more proteins will be broken down than produced) and thus - increase in oxygen demand.

Cats with hyperthyroidism, as a rule, show higher body temperature, which is due to the fact that the basal metabolism is raised and polydipsia and polyuria (i.e. they drink and pee more than the norm for this species).

Increased thirst in a cat with an overactive thyroid gland

The book symptoms of hyperthyroidism in cats will therefore be:

  • weight loss as an expression of increased metabolism,
  • polydipsia, that is, an increase in water consumption,
  • polyuria, i.e. more urine output,
  • polyphagia, i.e. increasing the amount of calories consumed,
  • vomiting, diarrhea,
  • tachycardia, or acceleration of the heart rate,
  • increased physical activity,
  • hypertrophic cardiomyopathy.

Hyperthyroidism and poisoning with thyroid hormones (thyrotoxicosis) lead to myocardial hypertrophy and high blood pressure, so it gives cardiac symptoms.

A characteristic symptom is a significant increase in appetite, although it does not always have to occur (significant heart failure or an advanced cancer process will give symptoms of anorexia), and yet the cat will lose weight.

The animal is losing weight loses skin elasticity, which makes it strange as if there was too much of it.

Sick cats may show clear stimulation and excessive physical activity, and at the same movement disorders.

Even slight physical exertion can accompany it breathing with the mouth open, as a word breathlessness if dilated pupils.

An overactive thyroid gland in a cat is fatigue after a short activity

Muscle tremors, dyspnoea, physical failure, and at the same neglecting the toilet, bad coat appearance if muscle atrophy is a typical image of a cat showing overactive thyroid gland.

A characteristic symptom associated with hyperthyroidism in cats is neuromyopathy manifested weakening or good-natured crook of the neck.

The severity of fatigue can be so great that in some cases cats need to rest even after a little effort of walking from one place to another. Fortunately for us, this extreme fatigue is not always the case.

You must remember that the symptoms of the disease will not be equally severe in all cases and that when the cause of hyperthyroidism is a mild thyroid hyperplasia, the symptoms will develop slowly, gradually - unlike thyroid cancer, which most often causes symptoms to appear suddenly and quickly.

We should also remember about congestive heart failure in advanced cases and hypertension and do not combine it with the progressive aging process, but always try to determine the cause of this condition.

Development occurs in hyperthyroidism hepatopathy, that is liver enlargement as a consequence of its hypoxia and increased oxygen consumption in the digestive system.

So we see how diverse the clinical symptoms can be in the case of this disease and how sometimes it will be difficult to make a diagnosis and implement effective treatment based on them.

What else can we tell in a cat suffering from hyperthyroidism??

The vast majority of sick animals will show enlargement of the thyroid gland, which can be found on palpation by palpating the cat's neck.

Benign hyperplasia will manifest itself as bilateral enlargement of the thyroid lobes, while malignant tumor as a rule, it only affects one lobe.

In conclusion, we can see how serious and diverse symptoms accompany hyperthyroidism, which results from the role this gland plays in regulating metabolism and how difficult it is sometimes to make a certain diagnosis.

Disease diagnosis

X-ray examination is used to show tumor metastasis

In a clinical trial, it is extremely important to know the symptoms of the disease, which do not necessarily appear in their entire palette in every case.

As I mentioned earlier, hyperthyroidism is most common in older animals, so it should always be taken into account when examining cats in their prime and older ones, i.e. over 8-10 years of age.

So we start the diagnostics from medical interview supplemented by a palpation of the thyroid area, where we can feel the enlargement of the gland.

Only then do we carry out blood laboratory test, which can be shown by:

  • increase in liver enzymes:
    • ASPAT,
    • ALAT,
    • ALP,
    • GLDH,
    • AP,
  • hyperglycemia, i.e. elevated blood glucose levels,
  • kidney failure.

Morphology it usually shows raising the level of white blood cells.

These are, of course, non-specific results and cannot be used to diagnose the disease unequivocally.

For this we need to conduct a more thorough, specific determination of the level of thyroid hormones, and specifically mark it total thyroxine concentration in the blood, that is T4.

The increase in serum T4 levels with other clinical symptoms clearly indicates the process of organ hyperfunction.

A correct T4 level in a cat with clinical symptoms and an enlarged thyroid does not rule out hyperthyroidism and requires repeat tests in a few months.

T4 determination is a cheap, simple and, most importantly, extremely reliable and reliable method in diagnosing hyperthyroidism in cats.

We should also remember that the determination of T3, fT3 and fT4 has little diagnostic significance and is not fully reliable, so it is not recommended.

Remember that hormonal tests must be performed in specialized veterinary laboratories, not human ones, because only such results will be of diagnostic value and will be certain.

You can also perform other tests, such as TSH stimulation test, T3 braking test if determination of the level of TSH in the serum.

It certainly is helpful in diagnostics ultrasound examination of the thyroid gland, which determines the size, structure and location of the gland and allows you to determine whether a pathological process is taking place in it.

X-ray examination is used to show possible tumor metastases.

Hyperthyroidism gives cardiological symptoms, so by examining the heart, we can also show some pathological processes.

So we can use research EKG, if an echo of the heart in order to make a certain diagnosis.

Thyrotoxicosis causes myocardial hypertrophy, leads to his failure and destruction, which will be reflected in the study echocardiographic.

Since we have a diagnosis, let's move on to therapeutic management, i.e. treatment.

Treatment of hyperthyroidism in cats

In therapeutic management, we can use:

  • pharmacological treatment,
  • surgery,
  • less available with us - radiotherapy.

In general, we strive to reduce the concentration of thyroid hormones and their impact on the body, and this goal is achieved using one of the above-mentioned methods.

Surgical removal of the thyroid gland

Surgical removal of the thyroid gland

Thyroidectomy, that is surgical removal of the thyroid gland It is considered an effective therapeutic procedure to eliminate hyperthyroidism.

Of course, it should be performed by a surgeon with extensive experience, so as not to damage the parathyroid glands located on the posterior pole of the thyroid lobes or nerves (mainly the recurrent laryngeal nerve) during the procedure.

When deciding to undergo surgery, we must remember about the risks associated with it, especially in the context of arterial hypertension, hypertrophic cardiomopathy or renal failure, and difficulties with anesthesia.

In order to minimize the potential risks associated with the procedure itself, you can apply pharmacological treatment for 4-6 weeks prior to the procedure. For this purpose, we use:

  • sympatholytic drugs,
  • thyrostatic drugs,
  • high doses of iodine (less available from us).

Removal of the thyroid gland will of course drop in hormone levels, hence the necessity of them serum control and supplementation.

In the postoperative period, we should also control calcium level, to check if the parathyroid glands are not damaged by accident.

In case of thyroid cancer, which covers one of the lobes, only the diseased lobe is removed, and the other healthy one remains and produces thyroid hormones at the appropriate physiological level.

Drugs for hyperthyroidism in a cat

The goal of pharmacological treatment is to lower the level of thyroid hormones without surgical removal. They are also used when preparing the patient for surgery.

Remember that the constant administration of drugs does not lead to a permanent cure, but only inhibits the symptoms of the disease, which will return once their administration is stopped.

The drug commonly used in this situation is metimazole (thiamazole) in the preparation Metizol at the initial dose of 1.25-2.5 mg per cat 2 times a day (3-5 mg / cat 3 times a day). The effectiveness of such a procedure is high and oscillates around 90%.

Sometimes, however, there are side effects in the form of disorders in the red cell system, which can lead to hemorrhages, liver dysfunction or kidney if gastric symptoms.

So we must regularly perform the appropriate Blood tests, to quickly identify potential disturbances and prevent them.

Side effects disappear after the drug is discontinued, which is extremely beneficial from our point of view.


Treatment with radioactive iodine, although it is a highly effective method, it is not performed in Poland.

Radioactive iodine isotopes administered subcutaneously are captured by thyroid cells, and by emitting β radiation, it destroys overactive cells.

This therapy has a very high cure rate, but is associated with high cure rates a nuisance for the owners.

Cats subjected to it must be isolated from the environment for a longer period (at least a month) so that by emitting radiation they do not pose a threat to the people around them.

For this purpose, of course, a number of specific radiological requirements must be met, hence centers offering this type of treatment are not widely available.

When using this method, development should also be taken into account hypothyroidism as a complication, but its treatment is usually not problematic.

In case of congestive heart failure we use treatment to eliminate pulmonary edema (diuretics e.g. furosemide) and specific cardiac treatments to support a failing heart (digoxin, ACE inhibitors if vasodilators).

We should not forget about treatment as well high blood pressure, which is often associated with an overactive thyroid gland.

Of course, it would be best to carefully examine its height beforehand and then introduce the appropriate medications (e.g. benazepril 0.25-0.5 mg / kg 1x daily, enalapril 0.5 mg / kg 1x daily).

Untreated disease leads to progressive damage to the heart muscle, its failure, pulmonary edema, kidney and liver failure, and consequently poses a serious threat to life, and through its symptoms significantly reduces the quality of life of an otherwise elderly cat.

Therefore, it is extremely important to identify causal and symptomatic treatment as soon as possible.

The prognosis for hyperthyroidism is v good most of the time.

Cautious it is only in the presence of other diseases, such as heart disease or kidney failure.

Diet of an overactive thyroid gland in a cat

They can be helpful in treating an overactive thyroid gland specialized feed.

They contain nutrients at the appropriate level, which support the healing process:

  • iodine,
  • phosphorus,
  • sodium,
  • taurine,
  • omega 3 fatty acids.

Food for a cat with an overactive thyroid gland is for example Hills Feline Y / D thyroid problems.


In conclusion, it is worth emphasizing once again that in the case of hyperthyroidism in cats, it is extremely important to diagnose it as early as possible.

Without fully knowing the factors that cause the disease, we cannot prevent hyperthyroidism in cats.

However, we should not give up too easily, because early diagnosis and treatment measures will effectively prevent the development of secondary pathological changes related to heart, kidney, liver or heart failure.

Every owner of a cat in the prime or older age should from time to time perform a control blood test with the determination of the level of thyroid hormones.

This is because such action will allow you to catch the disease earlier, and effective therapeutic action will ensure a long life for our little one - which I sincerely wish all cat owners.

Sources used >>

Leave Your Comment