In cats, hyperthyroidism results from functional thyroid
adenomatous hyperplasia (growth of the glandular
cells) or adenoma (a benign tumor). Rarely, a cancerous
tumor (adenocarcinoma) causes feline hyperthyroidism.
One or both lobes of the thyroid gland are involved (70
percent of cases involve both thyroid glands). Most cats
with hyperthyroidism are ten years of age or older.
The most common clinical signs include hyperactivity,
weight loss, increased appetite, vomiting, or diarrhea. In
some cases (apathetic hyperthyroidism, which occurs
in approximately five percent of cases), the cat does not
experience these classic signs. Instead, the cat may act
more lethargic, eat less, and generally act depressed or
Diagnosis is made by finding elevated thyroid hormone
levels on a blood profile. Other common geriatric diseases
whose clinical signs mimic hyperthyroidism, such as kidney
disease and diabetes, should be screened for as well.
Secondary problems such as mild liver or heart disease
usually resolve when the underlying hyperthyroidism is
treated. Because older cats can also have kidney disease
that may worsen if the hyperthyroidism is treated, cats
with hyperthyroidism must be carefully screened for kidney
disease prior to treatment of hyperthyroidism.
Principal Natural Treatments
Glandular Therapy—is recommended for cats. It uses
whole animal tissues or extracts of the thyroid gland.
Current research supports this concept that the glandular
supplements have specific activity and contain active
substances that can exert physiologic effects.
While skeptics question the ability of the digestive
tract to absorb the large protein macromolecules found
in glandular extracts, evidence exists this is possible.
Therefore, these glandular macromolecules can be absorbed
from the digestive tract into the circulatory system and may
exert their biologic effects on their target tissues.
Several studies show radiolabeled cells, when injected
into the body, accumulate in their target tissues. The
accumulation is more rapid by traumatized body organs
or glands than healthy tissues, which may indicate an
increased requirement for those ingredients contained in
the glandular supplements.
In addition to targeting specific damaged organs and
glands, supplementation with glandular supplements may
also provide specific nutrients to the pet. For example,
glands contain hormones in addition to a number of other
chemical constituents. These low doses of crude hormones
are suitable for any pet needing hormone replacement, but
especially for those pets with mild disease or those whom
simply need gentle organ support.
Glandular supplements also function as a source of
enzymes that may encourage the pet to produce hormones
or help the pet maintain health or fight disease. Finally,
glandular supplements are sources of active lipids and
steroids that may be of benefit to pets. The dosage of
glandular supplement varies with the product used.
Astragalus—is used to strengthen the immune system
and acts as an antibacterial and anti-inflammatory herb.
As a result, many doctors prescribe this herb for pets with
various infections and for those with chronic illnesses,
In cats, astragalus is often recommended for the
treatment of hyperthyroidism. It can also be used to help
the body recover from long-term steroid therapy and for
pets with kidney disease, as this herb improves kidney
Astragalus membranaceous is safe, but other species
of astragalus can be toxic. Do not use in pets with diseases
resulting from an overactive immune system (autoimmune
Bugleweed—may be useful for cats with mild
hyperthyroidism. Frequent doses of the herbal extracts must
be given for several days before any result may be detected.
Like digitalis, bugleweed can be helpful in heart conditions
in which the heart's contractions should be strengthened
and the rate (pulse) decreased.
Bugleweed can also act as a diuretic and remove excess
fluid from the lungs, as might occur in congestive heart
failure. It can be useful for pain relief and does not contain
salicylic acid so it can be used safely in cats. Do not use in
Lemon Balm—may be useful in cats to decrease thyroid
output and possibly decrease blood pressure. As with the
other herbs mentioned, controlled studies are hard to find,
and herbs may not be helpful in cats with severe disease.
The dosage of herbs varies with the product used.
Other Natural Treatments
Other therapies include homeopathies (homeopathic
tyhyroidium), and whole food supplements. Use raw broccoli
mixed in a homemade diet, as much as possible; or if the
cat does not eat raw broccoli, use a whole food broccoli
supplement such as Phytolin from Standard Process.
These can be used in conjunction with conventional
therapies, as they are unlikely to be effective by themselves
in most patients. The natural treatments are widely used with
variable success but have not all been thoroughly investigated
and proven at this time. As with any condition, the most
healthful natural diet will improve the pet's overall health.
Because vegetables such as broccoli and cabbage can
depress thyroid hormone if eaten in large amounts, they
should not be fed (or fed in only in small amounts) to dogs
with hypothyroidism. The herbs mentioned above, while
useful in treating cats with hyperthyroidism, should be
avoided in dogs to prevent a worsening of clinical signs.
Treatments to avoid in dogs include astragalus, bugleweed,
and lemon balm.
Three conventional therapies are recommended for cats
with hyperthyroidism. Surgical removal of the thyroid
gland can be performed. However, anesthesia is needed
for this procedure; and while geriatric cats can be safely
anesthetized, the other options for treatment usually do
not require anesthesia and are usually preferred. Second,
surgery, especially in severely hyperthyroid cats, is
associated with significant morbidity (illness and trauma)
and mortality, as well as the chance for postoperative
calcium imbalances due to damage or inadvertent removal
of the associated parathyroid glands.
Medical therapy, most commonly with methimazole
(Tapazole), is another conventional option. The medicine
is given for the life of the cat and is very successful in
lowering levels of thyroid hormones. Rare side effects
include lack of appetite, vomiting, lethargy, facial
dermatitis, and low red cell, platelet, and white blood cell
counts. Liver disease is also a possible side effect. Cats
experiencing abnormal blood or liver profiles or facial
dermatitis are at risk of future serious side effects and
must have their medication stopped and another form of
The third and most commonly used treatment for cats
is radioactive iodine. While this sounds quite drastic, it
may be the safest conventional treatment for hyperthyroid
cats. Side effects are extremely rare, and most cats are
completely cured after one treatment. Hypothyroidism, or
low thyroid output, is a rare side effect of treatment that
can easily be treated with thyroid replacement hormone if
needed. Because radioactive iodine cures the hyperthyroid
conditions, and because cats with underlying kidney
disease could develop kidney failure when cured of their
hyperthyroid conditions, it is essential that cats be screened
for kidney disease prior to radioactive iodine treatment.
The major concern among owners is that cats treated with
radioactive iodine must be hospitalized for one week or
more until they are no longer excreting radioactive iodine
in their urine or feces.
A fourth, newer proposed treatment is injection of
ethanol directly into the affected thyroid gland using
ultrasound to guide the procedure (percutaneous ethanol
ablation). Early studies appear positive, although some
cases involved laryngeal paralysis secondary to leakage
of ethanol from the thyroid gland and inflammation of
the recurrent laryngeal nerve. More research is needed
to determine whether percutaneous ethanol ablation will
become a safe and effective therapy for treating feline