The thyroid glands are paired, and sit on each side of the airway or trachea. The hormones produced here affect the metabolic rate for every system in the body. Hyperthyroidism occurs when too much hormone is produced. The most common cause is due to a non-cancerous mass in thyroid gland tissue; but cancerous tumors due occasionally occur in 2-3% of hyperthyroid patients. Both glands are affected in 80% of cats. In some cases, felines can have additional thyroid hormone production in unusual areas, most commonly in the chest.
Multiple symptoms can occur with hyperthyroidism, and many organ systems can be affected. Almost all patients show weight loss, with the majority of kitties eating more as they try to ingest enough calories to compensate for their increased metabolism. Almost half of the cats with this disease will vomit, drink more water, and urinate more. A third of hyperthyroid patients will show increased activity, irritability, vocalization and/or anxiousness. And many have an unkempt coat. Diarrhea can also routinely occur.
Additional physical changes can be found on examination. A rapid heart rate is often present, which over time can thicken the walls of the heart and lead to heart failure. Many patients have high blood pressure and heart murmurs. High blood pressure if left untreated can be damaging to several vital organs including the kidneys, liver, eyes, and brain. An increase in the size of the thyroid gland may be palpable on exam. Symptoms may be subtle at first; but become more severe as the disease progresses.
Hyperthyroidism is diagnosed with blood work. Because many of the symptoms are suggestive of problems with kidney, liver and elsewhere; a blood panel and urinalysis will typically be run. The T4 thyroid level is the value that is most commonly monitored; in some cases other thyroid testing may be recommended. Blood pressure may be evaluated, and additional heart testing may be suggested. A Technetium scan can be done at referral facilities, and it identifies the location of the abnormal thyroid tissue.
The cornerstone of treatment for most patients is lifelong, twice daily medication. This treatment option is relatively inexpensive; but does require blood monitoring usually every 6 months. It is also recommended to monitor blood pressure. Most patients show significant improvements with symptoms within 2-8 weeks of starting therapy. Sometimes dosages need to be modified over time, and side effects are usually minimal. Medication does not cure the disease; but it works to decrease thyroid production, and in turn reduce and/or prevent long term bodily harm.
Other treatment options that can be curative do exist at specialty facilities and include surgery, radioactive iodine, and some other potential treatments that are currently being evaluated. The safety of these additional therapies depends on the health status of the patient. Surgical removal of the thyroid glands does require anesthesia, and can allow for potential damage to the parathyroid glands which surround the thyroid glands. Surgery is also not a good option if there are additional sources of thyroid production in the body. Radioactive-Iodine treatment can only be conducted at a facility that is equipped to handle radioisotopes. Felines are quarantined with no visitors normally for 5-10 days depending on how long the levels of radioactive iodine take to decrease in their bodies. Sometimes additional treatment is needed.
Hyperthyroidism is a serious health risk for cats. Any feline that demonstrates typical symptoms should be evaluated and receive treatment as soon as possible. Your veterinarian can help in the diagnosis and treatment recommendations. Routine blood work is an important tool in protecting the health of your cherished feline