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Feline Hyperthyroidism

Feline Hyperthyroidism is caused by an increase in production of thyroid hormones from the thyroid glands, which are situated in the neck. Thyroid hormones are responsible for regulating many body processes and when too much hormone is produced the clinical signs can be quite dramatic, and cats can become seriously ill. Thyroid hormones also help control the body’s metabolic rate and cats with hyperthyroidism tend to burn up energy too rapidly and typically suffer weight loss despite having an increased appetite and increased food intake.

Fortunately, the vast majority of cats that develop hyperthyroidism can be treated very successfully and most cats will make a complete recovery.

Signs of Hyperthyroidism:

  • Weight loss
  • Usually a good or increased appetite
  • Increased thirst
  • Increased activity, restlessness or irritability
  • An increased heart rate
  • A poor and unkempt hair coat
  • Rapid toenail growth
  • Mild to moderate diarrhea and/or vomiting
  • Some cats will be noticeably intolerant of heat and seek out cooler places to sit
  • Some cats (especially advanced cases) may also pant when they are stressed

What happens if left untreated:

  • Excess thyroid hormone affects virtually every organ in the body. It increases metabolism, causing weight loss despite increased appetite. Fat and muscle are burned away. If left untreated, hyperthyroidism is a wasting disease.
  • As metabolism increases, the heart works harder. This muscle pump changes in size and dimension due to the constant stimulation. Eventually, this leads to heart failure.
  • High blood pressure
  • Kidney damage
  • Uncontrolled hyperthyroidism increases anesthetic risk

Treatment Options for Hyperthyroidism

There are three (3) main options for treating hyperthyroidism in cats.

Medical management (drug therapy)

Anti-thyroid drugs act by reducing the production and release of thyroid hormone from the thyroid gland. These medications do not provide a cure for the disease, but they do allow either short-term or long-term control of hyperthyroidism. The advantages of medication are that the drugs are readily available and relatively inexpensive. Some cats may experience side effects, however, that include vomiting, anorexia, fever, anemia, and lethargy. Lifelong treatment, usually involving twice-daily oral dosage, will be required-and for some owners and cats, that dosage schedule may be difficult to achieve.

Routine blood tests should be done periodically during treatment, to evaluate the effectiveness of therapy, to monitor kidney function, and to look for actual or potential side effects.

To recap:

  • Does not cure the disease or kill the thyroid tumors; in fact, the tumor can keep growing, making medical management less and less effective.
  • Causes harmful side effects like nausea, vomiting, lethargy, lack of appetite and hair loss/facial scabbing.
  • Causes loss of vital white blood cells and blood clotting abilities.
  • Causes long-term damage to liver and kidneys.
  • Damages owner-pet relationship by requiring pilling, 1-3 times daily.
  • Increases the need for blood tests to monitor thyroid hormone levels and potential side effects.
  • Costs $500-$700 per year, for the rest of your cat’s life.

Surgery – Surgical Thyroidectomy

Removal of the thyroid glands-surgical thyroidectomy- is a relatively straightforward surgical procedure that has a good success rate. The advantage of surgery is it is likely to produce a longterm or permanent cure in most cats, and therefore eliminates the need for long-term medication. This surgery requires general anesthesia, and there might be added risks if older cats have heart, kidney, or other problems that could cause complications. There is a major risk, associated with the surgical procedure itself, of causing inadvertent damage to the parathyroid glands, which lie close to or within the thyroid glands and are crucial in maintaining stable blood-calcium levels.

To recap:

  • Requires anesthesia.
  • May damage parathyroid glands.
  • Creates difficulty in identifying/removing the entire tumor.
  • Leads to persistence of Hyperthyroidism post-surgery (80% of cases already have another tumor on the opposite side that will become clinically significant within 1.5 years).
  • Costs $700-$1300 for one surgery.
  • Is often performed in two surgeries.
  • Leaves thyroid tissue in the chest where the tumor can recur.
  • Leaves many cats still needing radioactive iodine treatment, even after undergoing one or more surgeries.

Radioactive Iodine Therapy

Radioactive-iodine therapy is the treatment of choice and the only consistent cure for cats with hyperthyroidism. During treatment, radioactive iodine is administered as an injection and is quickly absorbed into the bloodstream. The iodine is taken up by the thyroid gland but not by other body tissues. The quantity of radiation destroys the abnormal thyroid tissue but does not damage the surrounding tissues or the parathyroid glands. The majority of cats have normal hormone levels within one to two weeks of treatment.

The advantages of radioactive-iodine therapy are that the procedure is curative, has no serious side effects, and does not require anesthesia. It does, however, involve the handling and injection of a radioactive substance that is only permitted at facilities specially licensed to use radioisotopes. The radioactivity carries no significant risk for the cat, but precautionary protective measures are required for people who come into close contact with the cat. A treated cat has to remain hospitalized until the radiation level has fallen to within acceptable limits. This usually means the cat will need to be hospitalized for approximately three days after treatment. Because of strict treatment guidelines, Long Animal Hospital & Emergency Center will not allow visitors.

Radioactive-iodine therapy is curative in approximately 95% of all hyperthyroid cases. For the few cats where hyperthyroidism persists, the treatment can be repeated. Rarely, a permanent reduction in thyroid-hormone levels—hypothyroidism—occurs after radioactive-iodine treatment. If this is accompanied by clinical signs such as lethargy, obesity, and poor hair coat, then thyroid-hormone supplementation may be required.

How Our Treatment Works

Radioactive iodine therapy is an extremely effective treatment for treating feline hyperthyroidism. Candidates for the radioactive iodine therapy should be relatively healthy cats that have been off their feline hyperthyroid medications for at least two weeks prior to treatment.

The treatment protocol is as follows:

  • Patients are admitted on Monday and in most cases will be discharged on Wednesday afternoon.
  • Upon admission, patients are provided with a comprehensive health evaluation to ascertain the extent of the problem and to develop a therapeutic approach.
  • A low dosage of radioactive iodine is administered to the patient through a single subcutaneous injection.
  • The agent is accumulated and concentrated in the abnormal parts of the thyroid glands.The iodine destroys the diseased tissue, while healthy thyroid tissues are not affected.
  • Once the agent is injected, the patients are kept in a specially designed isolation area and are monitored for 2 to 3 days while the radioactive agent is cleared from the body.
  • Due to radiation safety regulations, visitors are not allowed.