Hyperthyroidism in Cats


A problems with a cat’s thyroid is usually the overproduction of thyroxine – hyperthyroidism – with the opposite condition – hypothyroidism – being much less common. The overproduction of the thyroid hormones can be caused by an enlargement of the thyroid itself, which can usually then be felt by a vet on examination or, more unusually, the migration of thyroid tissue to other parts of the body, where it will continue to overproduce the hormone. A thyroid tumour may also be responsible, unless the tumour becomes necrotic, at which point hypothyroidism will occur.

Symptoms of hyperthyroidism in Cats

As with so many conditions the symptoms of hyperthyroidism are similar to those of other diseases including low thyroxine. The onset of hyperthyroidism may be quite insidious and as always a good knowledge of your cat and its normal behaviour will set you in good stead if a thyroid problem is suspected. The basic condition which is affecting the cat is a huge increase in metabolic rate, which will mean that all processes are quicker or to excess; so at cellular level, all chemical changes happen very fast, requiring an increased food intake. For a while, this will be adequate and the cat will not lose weight but eventually more food will not be enough and then the animal will lose weight, whilst still eating increased amounts of food.

Thirsty Cats

For similar reasons, the cat may also drink a lot. This leads many owners to suspect diabetes in the first instance. The cat’s coat will also probably become rather tatty looking and the animal may experience vomiting and diarrhoea, although if it is an outdoor cat this may not be spotted. An owner is unlikely to notice the increased heart rate which is also a symptom, although if the cat can be induced to sit quietly and be petted, this may be apparent. What will be noticed by the careful owner is that the cat will become very agitated and jumpy. It will begin to show an agitated facial expression, and appear to be always ready to run at the slightest noise or movement. Some cats are always nervous, of course, but if these signs begin in a cat which was previously calm, it should be taken immediately to the vet, even without other symptoms. 

Will my cat get better?

Thyroid tumours in cats are rare, so the cause of the hyperthyroidism is almost certain to be non-life threatening, but the cat will not recover from hypothyroidism as such in that it will need lifelong medication. After the first three weeks when the cat will be given a starting dose of thiamazole to reduce the hormone production, the dosage will be monitored into the permanent one by use of regular blood tests. It is important to monitor thyroxine levels to make sure the cat does not begin to become hypothyroid; this will present as lethargy and weight gain and if you notice this the cat must have a blood test immediately. These will be reduced to as few as one a year if the cat tolerates the medication well.

Old Age

As the cat gets older – and this condition is anyway more common in an older cat – it will probably need an adjustment in dose as its metabolism naturally slows with age. The only time that euthanasia would even be considered for hyperthyroidism would be if the cat or its owner could not tolerate the daily administering of the tablets. Some cats really hate pills and so every dose becomes a nightmare, upsetting the cat and its carer.

Can hyperthyroidism be prevented?

If your cat is suffering from hyperthyroidism it is only natural to wonder if there was anything in its care or environment which could have caused it, but this is strictly a physiological condition which could not be foreseen or prevented by different care. The only thing which an owner can add to the situation is to be vigilant over the cat’s health and if any of the signs of hyperthyroidism present, then to take the animal to the vet. This will not make the condition less serious in the long run but it will save the cat a lot of distress and misery, because the over anxiety caused by an over active thyroid is very upsetting, especially in an older cat or one who lives with several other animals, which can appear to the suffering animal to be very threatening, even though they will show no behavioural changes themselves.

Medication reminders

The cat’s pill regime will become a permanent part of the day and the administration of the tablet is not optional! The cat will improve in leaps and bounds as soon as the over production of thyroxine is under control, but this is not the cue to stop giving the tablets. The condition will immediately reappear. This medication is for life and this is why many vets counsel owners when thyroid problems are diagnosed, because not everyone can cope with such a stringent regime. Any carers when the owner goes on holiday must also have it explained to them that the tablet is a must not an ‘if you remember’ and so it is likely that the cat will have to go to a cattery – a not inconsiderable expense.

Even so, most owners will be so delighted to get their ‘old’ cat back, with its behaviour controlled and its coat back in peak condition that they will not mind giving a daily dose. There are many aids to pill giving available from pet shops these days and in time it will just become one of the little things which have to be done each day and the cat and its owner will soon think nothing of it.


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