Issue 4
Feline
Hyperthyroidism
Hyperthyroidism is a common condition of older cats. Hyperthyroid
simply means too much thyroid hormone is being produced by the thyroid
glands (located on the underside of the neck, next to the trachea).
The vast majority of cats with hyperthyroidism (98 percent) have
a benign tumor in the thyroid gland that is producing the excess
hormone. Approximately one to two percent of cats with hyperthyroidism
have a cancerous tumor in the thyroid gland. Hyperthyroidism is
typically a disease of older cats, with 95 percent of affected cats
being over 10 years old.
The symptoms of hyperthyroidism include:
- weight loss
- increased appetite
- vomiting
- diarrhea
- heart failure
- increased activity and vocalization
Common physical findings include:
- very thin body condition
- rough hair coat
- enlarged thyroid glands
- increased heart rate
- heart murmur
In most cases, diagnosis of hyperthyroidism involves doing blood
tests for the thyroid hormone level in the blood, kidney and liver
function tests, and a complete blood count. Hyperthyroidism can
also cause high blood pressure and changes in the heart walls (possibly
causing abnormal beats, a murmur or heart failure).
MEDICAL THERAPY
Tapazole is a drug that blocks the production of thyroid hormone.
It is used initially in most cats with hyperthyroidism. By lowering
the thyroid levels, it allows the cats to gain weight, decreases
vomiting, slows the heart rate, and lowers the blood pressure.
Therapy needs to be continued daily to keep the thyroid levels
normal. Disadvantages of Tapazole include: possible side-effects;
cost; and need for daily, lifelong treatment.
SURGERY
A thyroidectomy can be done to remove the thyroid glands, offering
a more permanent solution. The risks of surgery include the risks
of anesthesia, loss of the parathyroid glands (temporary or permanent),
and re-growth of thyroid tissue (causing a recurrence of the hyperthyroidism).
RADIOACTIVE IODINE TREATMENT
This is currently considered the ideal treatment for cats with
hyperthyroidism. It is safe and non-invasive. The treatment involves
injecting an isotope of iodine that seeks out the abnormal thyroid
tissue and destroys it, without affecting the normal thyroid tissue.
As the isotope is radioactive, the cat needs to be isolated in the
treatment facility for one to two weeks to avoid radioactive contamination.
The biggest disadvantage of this treatment is the cost. The treatment,
including hospitalization, blood screening and ultrasound, costs
approximately $1,000 and can be performed only at approved facilities.
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