Feline Hyperthyroidism: Symptoms and Treatments
October 04, 2012
Is your middle-aged cat experiencing increased thirst, appetite,
and urination? Is your furry friend losing weight or has a
change in behavior? If so, your family cat may have
This common disease is caused by an overproduction of thyroid
hormones, called T3 and T4, due to dysfunction of the thyroid
glands in the cat's neck. There are two of these glands, on
either side of the windpipe. Both glands are usually affected, but
this is not always the case. The symptoms mentioned previously are
not the only signs of hyperthyroidism; other symptoms include
vomiting, diarrhea, and a matted or greasy coat. These signs
start slowly and many owners may not initially realize that
something is wrong, said Dr. Audrey Cook, associate professor at
Texas A&M College of Veterinary Medicine & Biomedical
"A drop in body weight is often the first clue that a cat is
suffering from hyperthyroidism, which is one of the reasons why
regular vet visits are so important in older cats," Cook said.
If a cat starts exhibiting the symptoms of hyperthyroidism, a
trip to the veterinarian will confirm the diagnosis. The
veterinarian will perform a physical examination, which will
include careful examination of the neck. An enlarged thyroid gland
may be palpated, but a normal exam does not rule out the
possibility of hyperthyroidism. To confirm the disease, the
animal's thyroid hormone level will be checked through blood
Since thyroid hormones affect most organs in the body, it is
important to test a cat for the disease if it is suspected.
If left untreated, secondary problems can arise such as the heart
enlargement, with an elevated heart rate. Another problem
resulting from untreated hyperthyroidism is hypertension, or high
blood pressure. Both hypertension and heart disease caused by
hyperthyroidism will resolve with proper treatment of the thyroid
"Left untreated, the cardiac complications related to
hyperthyroidism can be life-threatening," Cook said.
Hyperthyroidism can be treated three ways: medication,
radioactive-iodine, or surgery.
Traditionally, medication is the main way to treat the
disease. For this option, an anti-thyroid medication is given
to decrease the amount of the hormones released from the thyroid
glands. This is relatively inexpensive, but the drug must be
given once or twice daily for the rest of the cat's life. Also,
side effects can include vomiting, anemia, lethargy and bone marrow
"Some owners have a hard time getting the medication in to their
cat," Cook said. "We can get it reformulated in to a liquid if this
is easier, and sometimes we use a product that is rubbed into the
ear and absorbed that way."
Radioactive-iodine therapy is becoming increasingly popular when
dealing with hyperthyroidism in cats. For this long-term treatment,
the cat is injected with the radioactive iodine, which destroys the
tissue of the overactive thyroid gland. Although this
procedure is usually very effective, it is more expensive and
requires the cat being confined to the hospital while the
"This is one of the best ways to treat this disease, and the
choice I made for my own cat when she was hyperthyroid," Cook
Surgical removal of the thyroid gland(s) is another option
available for this disease. Although the
long-term success rate is good, there is a risk of damage to the
parathyroid glands, located close to the thyroid gland. The
parathyroid gland is responsible for maintaining proper calcium
"We usually only recommend surgery if the gland is cancerous,
which is very rare, or if medication or radiation are not a
suitable choice," Cook said.
A veterinarian can help determine which treatment option is best
for your animal. In general, the prognosis for a cat with
hyperthyroidism is good. After treatment, long-term
monitoring of the thyroid levels will help ensure the cat continues
to live a happy life.
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