How To Diagnose Feline Hyperthyroidism


Hyperthyroidism, and known as “hyperthyroid disease,” occurs
when the thyroid gland enlarges, and starts producing excess amounts of thyroid
hormone (thyrotoxicosis). This is usually caused by a benign tumor on one or
both of the thyroid glands’ lobes. Although thyroid tumors can be cancerous,
the chances are only 2% to 5% of malignancy.

Not all symptoms will be seen in every cat, but any one or
two of them should be a strong indication that a veterinary examination is
indicated. Some of the symptoms that may be present are increased appetite,
unexplained weight loss and loss of muscle mass, irritability, frequent
vomiting, diarrhea, excessive thirst, weakness and lethargy.

In order for this to be diagnosed, the veterinarian will
palpate the cats’ neck area and may feel the enlarged gland. Since
hyperthyroidism can mimic the symptoms of other diseases, such as chronic
kidney failure or liver disease, a blood panel will usually show the “big
picture,” when combined with a thyroid-specific test, usually the T-4, which
will show thyroid levels. Elevated levels of T4 will usually indicate the
presence of this disease.

There are three standard treatment options available. Each
offers a strong possibility of returning the thyroid gland to normal function.

  • Anti-Thyroid medication (Tapazole) is an oral medication
    that is given twice daily. Many cats do well on this medicine, however, it has
    to be given to the cat every day for the rest of its life. It also requires
    regular blood tests to monitor hormone levels, so dosage can be regulated. The
    positive is that this is relatively inexpensive. As for the disadvantages, there
    could be some side effects that include vomiting, fever, anemia, lethargy and
    anorexia. Also, frequent veterinary follow up is needed.

  • Surgery can also be an effective treatment. Surgery is most
    often indicated when only one thyroid lobe is involved. An advantage of surgery
    is that it eliminates the need for long-term medication. Some disadvantages
    include possible damage to the adjacent parathyroid gland, hazards of
    anesthesia and if only one lobe is removed, a recurrence is possible.

  • The last treatment, which has become the “Gold Standard,” is
    Radioiodine Treatment. A single injection of radioactive iodine (I-131) is
    given under the skin (similar to a routine vaccination). The iodine is
    selectively taken up by the thyroid tissue and destroys it. No harm is done to
    normal tissue. The cat must remain in the vet hospital for an average of 5-7
    days until his radioactive levels are acceptable. One major advantage is that
    it provides a permanent cure in 95% of cases. A disadvantage is that the
    initial cost is higher, but it equal to about 18-24 months of care with the
    oral medication.

If your cat is showing signs of this disease, please call us
immediately so we can schedule an appointment.

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