thyroid gland is the body’s “speed control mechanism.” When it is set
on slow (hypothyroidism) hair falls out and doesn’t grow back, the energy
level is reduced, the heart rate slows and there is increased sensitivity
to cold. The dog (this condition is rare in cats) usually gains weight
with minimal food intake. Breeding animals lose interest or become infertile.
Delayed immune responses allow skin, urinary, or respiratory infections.
Sluggish nerve/muscle function can mimic hip or back problems. No one
dog will have all these symptoms and some are quite rare. However, the
condition appears to be very common.
would seem that diagnosing hypothyroidism would be a simple matter
of measuring the level of thyroid hormones but it’s not. There are
two hormones to measure in several different states or by different
methods. There are antibodies against both and some methods of measuring
confuse hormone with antibody resulting in false elevations. It is
also possible to measure thyroid stimulating hormone (TSH). Different
labs use different tests so results from one lab cannot be compared
illnesses and medications can temporarily lower thyroid hormones while
the gland itself is normal. Probably the most accurate diagnosis is
based on a combination of typical signs, low to extremely low thyroid
hormones and high TSH. In many cases if the blood work does not rule
out hypothyroidism treatment will be started to see if the symptoms
resolve. Once medication is started periodic monitoring is indicated
to make sure appropriate levels of thyroid hormone are maintained.
Giving thyroid supplements to a dog with a normal thyroid can damage
the other end of the spectrum hyperthyroidism speeds up the body.
This condition has become increasingly common in elderly cats. Symptoms
are usually weight loss in spite of a good appetite but some cats
quit eating and others suffer from frequent vomiting and/or diarrhea.
There may be a very rapid heart rate known as a gallop rhythm. Diagnosis
is usually easy—an elevated T4, one of the thyroid hormones, is almost
always present. If there are typical symptoms but the T4 is normal
additional tests may be needed.
are three methods of treatment available. One is surgery to remove
the affected gland. The surgery itself is not difficult but the age
and health of the patient certainly increases the risk. In addition,
there are some cases where the glands are not located in the usual
position and surgery may be attempted without success. Since the non
affected gland may develop the same condition a second surgery may
be necessary later. Also the para thyroid glands are closely attached
to the thyroids and their damage or removal can cause a sudden life
threatening drop in blood calcium.
treatment option is a tablet which is given two or three times a day
and suppresses thyroid function for a variable period of time—sometimes
as much as a year. Methimazole can cause side effects such as vomiting
and anemia. Regular monitoring for thyroid levels and blood count
should be done for the duration of time the cat is on the drug. Some
cats may be put on methimazole temporarily to improve health before
surgery or until the third option is available. The cost of monitoring
and the difficulties of giving most cats a pill two or three times
a day are the major drawbacks of this treatment. Another problem is
that eventually the drug will become ineffective.
third treatment option is radioactive iodine. This highly effective
therapy is very safe. It does not require anesthesia or repeated treatments
and monitoring. It is one simple intravenous injection. Because the
radioactive iodine concentrates in the gland it is destroyed no matter
where it is situated in the body. However it does not damage any surrounding
tissue so the parathyroid is spared. The cat must remain in the hospital
for 5-7 days while the radioactiviy fades and special precautions
must be taken for a few weeks after the cat returns home.
treatment is only available in a few locations and so it may be necessary
to wait a month or more for a turn. The cost is a little over $1000.
With effective treatment thyroid hormone levels reach almost to zero
but there does not appear to be any problem with hypothyroidism in
these cats. If the condition has been present for a good while there
may be permanent damage to the heart and/or kidneys so it is important
to evaluate these organs before treatment. Impending kidney failure
may be a reason to decline treatment as it will get worse when the
thyroid levels drop.