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Without going into a complicated physiology lesson, the thyroid is a vital link in the chain of any mammal’s endocrine system, which controls metabolic and activity levels. It also controls the production of calcitonin, which is necessary for proper calcium metabolism, vital for the cat’s bone and tooth health, as well as maintaining a healthy nervous system.


Symptoms of Hypothyroidism in your Cat

A cat with hypothyroidism has an underactive or inflamed thyroid gland producing the hormone T4 (easily measured by a blood test at the vet) and so its metabolism will be slower than usual. This will result in a sluggish animal, eating more than normal and therefore tending to put on weight. This is because the thyroid hormone which the animal is low on is the one which controls the conversion of food to energy; the body ‘knows’ it needs more energy, affecting the appetite areas of the brain and making the at eat more. For the same reason, the cat will drink more.


Greasy Hair and Skin

Alongside these symptoms, the animal’s coat will tend to ‘stare’, partially caused by the excessive grease production and the poor state of the animal’s skin and partly because there will be a tendency to groom excessively, sometime to the point of the coat coming out in clumps. By this point the cat will probably have become lethargic and if previously playful will be unwilling to interact and will seem dull. When grooming your cat you will probably notice that there is more dandruff on the skin, which may appear thickened if there are bare patches. If previously well trained to the litter box or cat flap, the cat may become incontinent in the house.


Prognosis for Hypothyroidism in Cats

The symptoms seem so severe and make the cat seem so unwell that it would be reasonable to suppose that this condition may well be fatal. Although this is not the case, the cat will certainly be feeling wretched and will eventually show joint disorders and may have problems with other organs if it remains untreated. Treatment is easily accomplished with oral administration of thyroxine, which is the hormone which the cat is lacking.


T4 Levels

It is important to measure the T4 levels before administration of any hormone replacement therapy as too much will cause the animal to develop hyperthyroidism, in other words the cat will have an artificially induced over active thyroid with its own problems and symptoms, just as distressing for the animal. But assuming that the drug therapy is tolerated well, the cat should be feeling much better within weeks of the dosage beginning. Weight will be lost, fur condition will improve and the cat will start to behave more like its old self. Most vets will check the T4 levels very frequently when the drug regime first starts, then it can be done six monthly.


Less Common Symptoms

In just a few cats with hypothyroidism there is an increase in aggression which is difficult to square with an animal that has become more sluggish and lethargic. It could just be that the cat is feeling so ill and depressed that it will lash out at other animals and even its owner. If this trait is noticed in the cat, it is important to keep it away from children as it may become very unreliable, even if previously friendly. As with the other symptoms, this personality change will be reversed with a correct drug regime. Other animals may develop compulsive behaviours outside of the excessive grooming already mentioned. The aggression and the compulsive habits can be alongside the other more overtly physical symptoms, but may also appear alone. This is why it is important that any change in a cat’s behaviour should be reported to a vet, as there may well be a simple explanation.


Possible Causes of Hypothyroidism

The thyroid is a butterfly shaped gland in the cat’s neck, with the two ‘wings’ spreading on either side of the windpipe. Tumours of the thyroid are usually easy to spot as there is noticeable swelling, but are relatively rare. The thyroid is controlled by the pituitary gland, which is in the brain, so a head injury, even an old one or one that caused no other symptoms may have caused it to malfunction for a while and cause a temporary ‘blip’ in thyroid activity. If the thyroxine levels prove difficult to stabilise, a vet may request an MRI to determine whether there is a more serious reason for the hypothyroidism than a simply underactive thyroid. 


Does my Cat Have an Underactive Thyroid?

Hypothyroidism in cats is relatively rare; when they have thyroid problems it is more likely to be over activity than under, but if it shows any of the symptoms outlined above, then the vet will check for thyroid issues very early in the diagnostic process. This is partly because the test is simple, cheap and non-invasive and will give a quick over-view of what may be the problem. Cats tend to gain weight when over ten years old and so a simple weight gain will not be enough to suggest hypothyroidism, but if the issues with coat and lethargy or depression are also present, then the condition, though rare in cats, will still be the likeliest cause.  

Problems with coat can be caused by many different reasons, so the mood changes and changes in appetite will be a very important part of the diagnostic process. When taking a cat to the vet, it is important to think about any changes in behaviour over the last months before the other symptoms set in, as this could decide the diagnosis.


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