Hyperthyroidism in Cats

Hyperthyroidism is a very common disease of older cats.  It is caused by the thyroid gland becoming overactive and speeding up the cat's metabolism.  It is easily diagnosed by blood tests and is usually treated with either tablets or an operation.  

What is Hyperthyroidism?

• Hyperthyroidism is a hormonal disorder caused by an over-active thyroid gland releasing too much thyroid into the cat's system.
• Thyroid controls the speed of the body's metabolism, so in cats with the condition it is going too fast.
• Hyperthyroidism usually affects cats over the age of 12 years and is very rare in cats below the age of 10.
• There are two Thyroid glands in the body which are positioned either side of the trachea (windpipe) in the neck.  Usually it is only one which becomes overactive and enlarged.
• In most cases of Hyperthyroidism the cause of the problem is a benign enlargement but in a small minority it is a malignant cancerous change.

Symptoms of Hyperthyroidism

• The main symptoms in cat's with Hyperthyroidism are;
  ◦ An increased appetite
  ◦ Weight loss
  ◦ Increased activity levels
  ◦ Increase vocalising
  ◦ Vomiting and diarrhoea – this is caused an increase in the motility of the guts under the influence of the high levels of Thyroid.
• These are all related to the speeding up of the metabolism.  When they first appear they are often mistaken by the cat's owner as signs of good health, which is understandable if an older cat suddenly develops a good appetite and a more playful and alert attitude.
• The cats can also have an unkempt coat, which simply reflects their poor state of health and often an anxious expression. (Vets will often describe cats as 'looking Hyperthyroid') 
• The symptoms often come on slowly over a period of weeks and months and it can take some time to realise there is a problem.
• When the cat is presented at the vet they will be suspicious of the problem because of the symptoms and may find other signs including
  ◦ A high heart rate – a normal heart rate for a cat is around 180-200 beats a minute but in Hyperthyroid cats it is often higher than 250.
  ◦ A palpable thyroid gland – often it is possible to feel the enlarged gland in the neck.

Diagnosing Hyperthyroidism

Treating Hyperthyroidism

• These It is very important Hyperthyroidism treatment is started as soon as the condition has been diagnosed.  The increased metabolic rate puts the bodies organs under great strain, especially the heart and the liver.
• Left untreated it can lead to heart failure, not to mention the fact that it is a very unpleasant disease for the cat.
• There are three different ways of treating Hyperthyroidism; tablets, surgery and radiotherapy.
• Regular tablets is the most commonly used treatment for the condition.  It involves giving the cat tablets once or twice daily and it is a lifelong therapy.  The tablet neutralises the excess thyroid once it is released from the gland but has no effect on the gland itself.
• An operation can be performed to remove the overactive gland.  It is a curative procedure, so once it has been done the cat will no longer require medication.  However, most vets will only remove the single, enlarged gland and in about 50% of cases, the disease will reoccur in the remaining one.  
• Few will remove both together as the normal gland is usually very small and difficult to find. Also, each Thyroid gland has a Parathyroid gland sitting on top of it.  These are very important  to keep the calcium levels in the body stable.  If one is damaged it is rarely a problem but if both are affected it can cause significant side effects.
• It is important before the surgery is carried out that the Thyroid levels in the body are normal, so even if the cat has surgery, they will need to take tablets beforehand.
• Radiotherapy is a completely curative procedure for Hyperthyroidism but it is only carried out at specialist centres and can be costly.
• It is a very easy treatment for the cat.  They are simply injected with a radioactive substance which collects in the Thyroid glands and destroys them completely.  However, they are then radioactive for some time and need to be hospitalised at the vets for four to six weeks while the medication leaves their system.
• Even if both the glands are destroyed, or in the case of surgery removed, it is very rare for a cat to have complications with Hypothyroidism (low Thyroid levels)

Prognosis

• The long term prognosis for a cat with Hyperthyroidism is very good provided the disease is well controlled.
• If the cat is on tablets, they will need to be regularly checked by the vet and have regular blood tests to ensure the disease is under control.
• If they have had surgery they need to be monitored for any recurrence of the disease but do not require any regular treatment.  

Please note, this is a advice only article.  If you have any concerns about this, or any other pet related subject, you must speak to your vet.