Feline hyperthyroidism

Feline hyperthyroidism

Hyperthyroidism is a disease that is being diagnosed more and more frequently in our cats and that usually affects the older ones. As the production of hormones is involved, their effects will harm the entire organism.

But with proper treatment, the life expectancy of our cat does not have to vary. In this SoyUnGato article we explain everything you need to know about this disease.

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What is feline hyperthyroidism?

In hyperthyroidism, the thyroid gland produces excess hormones, usually due to a benign tumor. In a small percentage of cases the tumor will be malignant. It is more common in elderly cats , especially from the age of eight. It is the most frequent endocrine pathology in these ages.

The thyroid gland is bilobed and is located in the neck. It secretes hormones that act on tissues throughout the body, so its failure can affect different organs.

These hormones are thyroxine or T4 and triiodothyronine or T3 . Iodine is an essential component of these hormones. Thyroxine controls energy production, which is needed to maintain normal basal metabolic rate, and is also involved in growth.

In hyperthyroidism, there is an increase in the synthesis and secretion of thyroxine, which increases the metabolic rate. The cause of the tumor is unknown but immunological, environmental, infectious, nutritional or genetic factors are considered. The latter have determined a lower incidence of the disease in Siamese and Himalayan cats .

Feline hyperthyroidism symptoms

The symptoms of hyperthyroidism are highly variable and, furthermore, nonspecific, which means that there will be multiple diseases that manifest with this same clinical picture.

That is why it is necessary for the veterinarian to perform diagnostic tests, such as blood and urine tests. In general, a cat with this disease will show symptoms such as the following:

  • Hyperactivity, although there are cats that will be lethargic.
  • Polyphagia, that is, an increase in food intake. Other cats, on the contrary, will present anorexia.
  • Weight loss, despite eating more.
  • Polydipsia (increased water intake).
  • Polyuria (increased urine output).
  • Vomiting
  • Diarrhea.
  • Coat in poor condition due to lack of grooming.
  • Dry hair and fine skin.
  • Zonas alopécicas.
  • Slight hyperthermia.
  • Tachycardia, murmur, or arrhythmias.
  • Accelerated breathing.- Breathing problems.
  • Excess of vocalizations.
  • Ventroflexión cervical.


How to diagnose hyperthyroidism in cats

The veterinarian can reach the diagnosis based on the symptoms, palpation of the thyroid gland, which is located in the neck but is not always touched, and a blood test that reveals the amount of thyroid hormones, preferably thyroxine or T4. That their values ​​are in normal ranges does not rule out the diagnosis because there may be mild or hidden hyperthyroidism.

In these cases, if there is a strong suspicion that the cat has hyperthyroidism, other tests such as T3 suppression or the response to another hormone, HRT, will be performed. Even so, it can sometimes be difficult to reach the diagnosis and it is necessary to repeat the tests. After confirmation, an ultrasound will give us more information on the state of the gland.

The scan is used for diagnosis always before operating or radio, if we choose these options explained in another section. It allows to know the state of the disease.

Conditions concurrent with hyperthyroidism

The excess production of thyroid hormones can concur with other diseases such as the following that, in addition, tend to delay the diagnosis of hyperthyroidism because in its course they will decrease the concentration of T4 :

  • Hypertrophic cardiomyopathy, which can be the cause of murmurs, tachycardia, arrhythmia, etc.
  • Renal failure, very common in elderly cats.
  • Gastrointestinal disorders, with anorexia, polyphagia, weight loss, increased frequency of defecation and stool volume, vomiting, diarrhea, etc.


What is the treatment for hyperthyroidism in a cat?

This disease presents the following treatment options from which the veterinarian must choose, taking into account the circumstances of each cat:

  • Thyroidectomy:is the removal of the thyroid or affected tissue. It is an intervention of intermediate difficulty, invasive and of moderate costs.
  • Medication:in the long term, which can have an impact on the cost, it inhibits the synthesis of thyroid hormone, but does not prevent the gland from increasing in size, so the cat must be checked every 4-6 months. In addition, it requires adjusting the dose. It can be administered in pills or gel.
  • Radiation –Radioactive iodine is used to destroy excess gland tissue. Healthy tissue is not affected. The drawbacks are that the cat must remain hospitalized for several days after the treatment, it can only be done in one of the few authorized centers because it is necessary to be able to handle and dispose of the waste and, in addition, it is expensive.

It is also necessary to take into account the concurrence with other diseases such as the ones we have mentioned, since it is what will determine the priorities in treatment. This can cause side effects such as anorexia, vomiting, lethargy, etc.

How long does a cat live with hyperthyroidism?

If the chosen treatment is successful, the prognosis is good. In the cases in which concurrent diseases have appeared, on the other hand, the prognosis is reserved. Age also worsens the prognosis.

The earlier the disease is detected, the better the life expectancy, hence the importance of performing annual tests on cats older than seven years, as they allow discovering this and other diseases even before they produce symptoms.


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