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Hyperthyroidism in cats

What owners can do for their cat, nutrition as a therapy and how high the life expectancy with hyperthyroidism is.

The thyroid gland of a cat sits in pairs on the neck, below the larynx. As in humans, the organ produces vital hormones. By definition, hyperthyroidism is a disorder of thyroid activity in which the organ produces too many hormones and releases them into the bloodstream. The high hormone level has consequences for the entire body.

In most cases, hyperthyroidism occurs for the first time in older cats from the age of eight. About every fifth animal from ten is affected. The disease, which is called “hyperthyroidism” in the technical language, is a chronic disease that is not curable. However, veterinarians can treat hyperthyroidism in such a way that the animal can live well with it.

Hyperthyroidism in cats: symptoms

An excess of thyroid hormones – they are called thyroxine (T4), triiodothyroxine (T3) and calcitonin – has consequences for the entire body. The hormones affect the cardiovascular system, energy metabolism, nerve cells and digestion. If the hormone level is too high, all these systems become overactive. Hyperthyroidism can be manifested by the following symptoms:

  • increased heart rate
  • hypertension
  • increased body temperature
  • increased appetite
  • increased thirst
  • increased activity
  • Weight loss
  • Uneasiness
  • increased urination
  • Hair loss
  • Putzunlust
  • Vomit
  • Diarrhoea
  • Weakness
  • Breathing difficulties
  • Nierenprobleme

Usually, cat owners first notice that their pet eats more and still loses weight. Affected cats seem restless and nervous, sometimes becoming aggressive or shy, although they were not before. Because they neglect grooming, the coat soon looks dull, shaggy and lackluster.

Hyperthyroidism in cats: when to see a veterinarian

Weight loss for no reason is always an alarm sign. Also, the causes of recurrent vomiting or constant diarrhea should be clarified by a veterinarian. However, the change in the behavior of the animal is also conspicuous in a thyroid disease: If cat owners have the feeling that something is wrong, they are often right. Unfortunately, the heart and kidneys have often already suffered damage when owners have their cat examined for the first time.

Hyperthyroidism in cats: treatment

There are several ways to treat hyperthyroidism in cats:

  • Medication: If the enlargement affects the entire thyroid gland, i.e. both halves, medication is the right – and cheapest – therapy. Administered once or twice a day, so-called thyrostatics such as thiamazole or carbimazole inhibit hormone production in the thyroid gland. Possible side effects of the tablets include loss of appetite, vomiting, anemia, liver problems and very rarely itching. However, most animals tolerate the remedies well and blood tests show an improvement after just a few weeks. Sometimes the dose needs to be adjusted later to get as close as possible to normal hormone levels. If the tablet administration proves to be difficult in a cat, there is the possibility of alternatively supplying the active ingredient to the ear via an ointment.
  • Radioiodine therapy: The expensive but permanently effective therapeutic measure is based on letting the thyroid gland absorb a radioactive form of iodine, after which the tissue decomposes and produces fewer hormones overall. The treatment works very well and quickly, but a decisive disadvantage is the radiation exposure: as a result, the treatment can not take place in every veterinary practice, but must be carried out in a specialized clinic, where the cat must stay for up to two weeks. Rarely, radioiodine therapy causes hypothyroidism.
  • Operation: If only one of the two halves of the thyroid gland is enlarged, it can be surgically removed. After that, the symptoms usually subside completely.
  • Feed changeover: The affected cat may be eligible for food that contains much less iodine than conventional food. Without iodine, the thyroid gland cannot produce its hormones, so their levels in the blood drop.

Cat owners should discuss with their veterinarian which treatment is right for their pet. Many then ask for measures from homeopathy, which also promises to have effective remedies for hyperthyroidism in cats. However, the preparations should at most be used in addition, because their effect has not been scientifically proven. Pet owners who treat their cat exclusively with homeopathy may miss the chance to get hyperthyroidism under control in time.

Life expectancy of a cat with hyperthyroidism

If left untreated, hyperthyroidism leads to the death of the animal in the long term, because the metabolism runs at full speed due to the high hormone level, which puts a heavy strain on the heart and circulation. In the final stages, cats would die from kidney, heart or liver damage.

Even with a very late start of treatment, it can lead to consequential damage such as changes in the heart, kidney damage or water in the lungs. The permanently high blood pressure also damages the retina, so that the cat can go blind as a result of hyperthyroidism.

An animal that has reached the final stage of the disease, owners do something good if they release it from its suffering. The veterinarian has the most experience with cats with thyroid disease – he knows when the time to euthanize them. Discovered early, however, hyperthyroidism in cats is well treatable, so that the animal can live with it for a long time satisfied and without pain.

Hyperthyroidism in cats: the right diet

The thyroid gland needs iodine to produce its hormones. Iodine is purely excluded through food, the body can not produce it itself. So it sounds understandable to give the sick cat a diet food that contains hardly any iodine in order to get the hyperthyroidism under control.

For cats that do not yet have too high hormone levels, a special diet can be a possibility of treatment. Often, however, such a food is not sufficient as a sole therapy. Cat owners should discuss with the veterinarian what is best for their pet. In any case, the food of a cat with hyperthyroidism should not be iodine-rich in order not to additionally fuel the disease through the diet. The veterinarian can assess whether the usual food is still an option, or whether a feed change makes sense.

Hyperthyroidism in cats: diagnosis

If the veterinarian suspects that a cat has hyperthyroidism, for example because he can already feel the enlargement of the organ, he will take blood from the animal. The hormone levels in the blood sample are often clear, but other diseases of the kidney and heart should be excluded.

It is also possible to measure the activity of the thyroid gland by scintigraphy as in humans – an imaging technique in which doctors inject weakly radioactive substances. In cats, the examination is often not necessary for a clear diagnosis. With the help of X-ray and ultrasound examinations, the veterinarian examines how badly the heart and other organs are already damaged.

Hyperthyroidism in cats: causes

The reason for the overactivity of the thyroid gland is its enlargement: because more thyroid tissue is present due to the growth of the organ, more hormones are also produced. Usually it is a benign growth.

Why the organ enlarges is unclear. In 30 percent of cats, a benign tumor (adenoma) on one of the two thyroid lobes is the reason for the hyperthyroidism, in 70 percent of the diseased animals, the entire gland is enlarged.

Rarely, the veterinarian discovers a malignant tumor (adenocarcinoma) on the thyroid gland, which confuses the hormonal balance.

An underactive thyroid, in which the organ produces too few hormones, hardly occurs in cats.


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