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Hyperthyroidism in cats
of the thyroid glands are common in older cats. They usually over-produce
thyroid hormone which increases the rate at which the body's organs work.
vary but include: increased appetite with weight loss, poor coat sometimes with
colour changes, increased heart rate, breathing problems, diarrhoea, occasional
vomiting, bouts of hyperactivity and/or "depression". Eventually the
cat becomes lethargic and inappetant, making diagnosis difficult.
the early stages the changes are reversible, later they are not and so it is
important to diagnose the condition as early as possible.
the glands are enlarged and the symptoms are typical then diagnosis is easy.
Unfortunately this is not always the case so we sometimes have to look for
increased levels of thyroid hormone in the blood. Unfortunately blood levels
vary during the day and also are reduced if the animal is unwell for any reason,
which may mean several blood tests
to confirm the diagnosis.
symptoms are caused by the increased levels of thyroid hormone and so treatment
is aimed at reducing these levels.
can be done medically with tablets that stop the thyroid
gland releasing thyroid hormone
or using radioactive iodine to destroy the
thyroid producing cells, or
surgically by removing the diseased gland or glands.
There is a new treatment available using a special food that has a very low
level of Iodine in it, which stops the body making thyoid hormone.
Medical Treatment. The aim is to
reduce the level of circulating thyroid hormone to normal. Because some cats
produce more hormone than others, the number of tablets needed daily will vary
from one cat to another. We
will need to monitor the cat's condition closely and medication will need to be
continued for the rest of the cat's life because if the tablets are stopped the
thyroid hormone level will rise again.
y/d, if used as
the sole food, will stop the thyoid gland making thyroid hormone, so controlling
the problem. However your cat will have to only have the special food for the
rest of itís life.
Radioactive Iodine can be used to
destroy the affected thyroid glands. This is the treatment of choice however the
cat then has to be hospitalised for a month at a referral centre and it is
advantages are that there are very few side effects, they then do not need long
term mediation and the conditions does not spread elsewhere in the body.
Surgical Treatment. The affected
thyroid gland(s) can be surgically removed. If
only one gland is involved this is usually
a relatively simple and painless operation with few post-operative complications
and means that the cat no longer needs routine medication. In most cases the cat
can go home later that day with no need for further medication other than
antibiotics for a few days. Most make a full recovery within a few days, eating
less, putting on weight and becoming much more settled.
in the long term other
growths can occur usually
in the other thyroid gland initially, but
this usually takes several years.
both thyroid glands have to be removed at
the same time there is a danger that the blood supply to the parathyroid glands, which
regulate the blood calcium level, can be affected and so we routinely
hospitalise them and monitor their blood calcium for two to three days after the
operation so we can start them on treatment if there are any problems.
in cats that need calcium supplementation, this is often only temporary.
hyperthyroidism makes cats a greater anaesthetic risk than normal and so we
often recommend a course of tablets before the operation and pre-operative blood
tests so we can ensure that the anaesthetic is as risk-free as possible.
rarely need thyroid tablets even if both glands are removed, probably because
there is other thyroid hormone producing tissue in the chest.
is therefore the
usual treatment in younger, fit cats or
for cats that are not happy to be given tablets daily for the rest of their
is the most common hormonal disease in cat. Left untreated it causes premature
aging and death, however the condition usually responds well to treatment and if
caught early there is a good chance of a complete recovery.
treatment we recommend varies enormously depending on many factors and so each
case is assessed individually.