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Hyperthyroidism
What is a hyperthyroidism?
Hyperthyroidism is a very common disease in older cats, caused by an over active
thyroid gland(s). Cats have two thyroid glands that lie on either side of the windpipe
and produce thyroid hormone. Thyroid hormone controls the speed at which the
body’s metabolism works. In the case of over active thyroid glands, where too much
hormone is produced, the metabolism is working ‘too fast’, resulting in signs of
disease. If left untreated, the condition will eventually prove fatal.
What causes Hyperthyroidism?
In the vast majority of cases hyperthyroidism is caused by a benign (non-cancerous)
tumour of one or both of the thyroid glands. The underlying cause of this change is
currently unknown, but is very similar to human hyperthyroidism, called 'toxic
nodular goitre'.
Rarely (in less than 1-2% of cases) a malignant (cancerous) tumour called a thyroid
adenocarcinoma can be the underlying cause of the disease.
Diagnosing the disease
Hyperthyroidism has a classic set of symptoms which include:
• weight loss
• good or increased appetite
• increased thirst
• hyperactive, restless, vocalising a lot
• poor coat condition
• occasionally vomiting or diarrhoea
Your vet may also pick up on abnormalities such as an increased heart rate which
would raise our suspicions. Sometimes an enlarged thyroid gland can be felt in the
neck.
However, not all cats will display all of these symptoms. Occasionally we see some
cats with hyperthyroidism that actually show the opposite set of symptoms with
lethargy, poor appetite and weakness.
In a lot of older cats a bit of weight loss could easily be dismissed as “old age”, so
it’s important not to ignore these things no matter how minor a concern may seem.
In the majority of cats a diagnosis can be confirmed with a simple blood test. We
measure the level of thyroid hormone in the blood stream and if it’s found to be too
high, your cat is hyperthyroid. It’s not always that simple, some cats will have a
normal blood result but do actually have the disease. We need to send a special
blood test off to the lab for these cats. The standard thyroid blood test costs about
£36. It’s more cost effective to include it as part of our standard screening blood
tests, which cost about £100 and checks other things like kidney and liver values.
Complications of Hyperthyroidism
Because hyperthyroidism affects mainly older cats, we often see a lot of other ‘old
age’ problems at the same time. We often do other tests such as heart scans or
additional blood tests, to check for these sorts of problems at the time of diagnoses.
Kidney Disease Thyroid hormone actually has quite a protective effect on the
kidney (but harmful effects elsewhere), so sometimes once the over active thyroid is
under control with medication we can unmask previously undiagnosed kidney
disease. We generally recommend blood tests and/or urine tests to check kidney
function when we diagnose hyperthyroidism.
Heart Disease Thyroid hormone increases heart rate, putting a lot of strain on the
heart. It’s common to see heart disease in cats that have hyperthyroidism. Cats will
quite often tolerate fairly advanced heart disease before the show any symptoms,
often it’s too late by the time we see them. We offer heart scans to better assess the
condition of the heart and provide treatment if it’s necessary.
High Blood Pressure High blood pressure can have a damaging effect on the
kidneys, eyes, brain and heart. Cats with high blood pressure need medication to
lower it.
Can it be treated?
Yes! Hyperthyroidism is a very manageable disease. There are 4 main treatment
options:
Tablets Medication reduces thyroid hormone production but does not cure the over
active thyroid. So treatment will be lifelong. The tablets are small, most cats will
accept them hidden in food or we can teach you the best way to ‘tablet’ a cat. There
are two types of tablets available: Vidalta or Felimazole, there are various doses of
both type of tablet. Each cat has different dose requirements, so we tailor treatment
to your cat's specific needs. A follow up blood test is recommended 3-4weeks after
starting treatment to make sure the dose is correct.
Generally these tablets are very well tolerated; we see very few side effects.
Occasionally some cats will have a mild tummy upset with these tablets, but it
normally stops after a few days and you do not need to stop giving the tablets.
Rarely some cats will have itchy skin, liver problems or low blood counts on this
medication. In these circumstances medication is stopped.
Cost: Obviously this varies depending on dosage. Average £40 per month. Pets who
are members of our healthy receive a discount on medication. A 6 month health
check is required for all pets on long term medication, a normal consultation fee will
apply for this visit. Follow up thyroid blood tests cost between £36 and £76
Special Diet - Hills y/d Useful for cats who refuse to take tablets. However, cats
are fussy eaters and some refuse to eat it. The diet is specially formulated to restrict
iodine intake, iodine is used by the thyroid gland to make thyroid hormone. If we
restrict iodine the body can't overproduce thyroid hormone. So like for tablets we are
managing the disease not curing it. For this treatment to be successful cats must eat
just y/d and NOTHING else. Small amounts of iodine are in pretty much everything a
cat would like to eat. So for cats that hunt a lot, cats that pinch the dog's food, cats
that pinch next door's cat's food, cats that pinch your food....this is probably not the
right option. As for tablets we recommend follow up blood tests to make sure
treatment is working.
Cost: 1.5kg bag of dry food is about £20, tins of wet food are about £2 each. This
may sound a bit expensive for cat food, but it’s not just cat food, its treatment too. If
you compare it to tablets plus the cost of average cat food, it actually works out
about the same.
Surgery We can perform an operation to remove the enlarged thyroid gland. This
provides a longer term treatment option than the diet or tablets, some cats are cured
after surgery. However, many cats develop hyperthyroidism later in life if the other
thyroid gland becomes affected. Some cats have extra thyroid tissue hidden
elsewhere in the body that isn't operable, so you could remove both thyroid glands
but still have a hyperthyroid cat. There are obviously risks involved with surgery,
particularly if there are complicating factors such as kidney disease or heart disease.
To reduce the risks involved, we always stabilise cats with anti-thyroid tablets prior
to surgery.
Attached to the thyroid gland is the much smaller parathyroid gland, which controls
calcium levels. Occasionally this can be inadvertently damaged during surgery, so
these cats need careful monitoring post-surgery, often we check blood calcium
levels.
Cost: On average surgery costs about £700, if blood tests/hospitalisation etc are
necessary extra costs will be incurred.
Radioactive Iodine Treatment This is a specialist treatment requiring referral
to a specialist centre. It is the only one of the treatments that is truly curative. It
involves your cat staying at the specialist centre for at least 1 week. An injection of
radioactive iodine is administered to the cat. This sounds a lot scarier than it actually
is; it’s a really safe and effective treatment. The radioactive iodine is only taken up
by the thyroid gland, so doesn't harm any other parts of the body, it just targets
thyroid tissue. This is particularly useful in those cats that have extra thyroid tissue
hidden about the body.
Cost: Varies a lot between cases, many cats need further tests before starting
treatment to make sure they are suitable candidates. On average the treatment costs
£1500-2000
What should I expect after treatment
starts?
Normally within a week of starting treatment, whether that be tablets or diet (or
surgery/iodine treatment) you should see a difference in your cat. Appetite should
return to normal, they should start to gain weight and hyperactive behaviour should
calm down. In fact many owners worry their cat is unwell after starting treatment
because they aren't eating so much and are just sleeping all day. Remember most of
these cats are elderly cats; it’s abnormal for them to be running about like a kitten
and eating like a gannet. However, if you are at all worried about your cat once
treatment has commenced, please just contact us.
What happens if I don't treat my cat?
If left untreated cats will continue to lose huge amounts of weight, they will literally
waste away. The racing metabolism puts huge strain on the heart; associated high
blood pressure will have negative effects all over the body. These cats are constantly
starving hungry; their quality of life is undoubtedly detrimentally affected.
What's the prognosis?
With treatment hyperthyroid cats lead pretty normal lives. The prognosis is very
good. For cats with complicating factors such as kidneys disease, the prognosis is a
little more guarded, but many of these cats do very well with appropriate treatment
too.
If you have any questions or concerns regarding hyperthyroidism please just ask one
of our team and we'll do our best to help you.
01527 831 616