INFORMATION ON IODINE 131 (I131)

What is Hyperthyroidism?

Why Iodine 131 (I131) is the treatment of choice

Admissions Requirements

How long will my cat be in the hospital?
 
WHAT IS HYPERTHYROIDISM?
Hyperthyroidism is when the thyroid gland produces an excessive amount of thyroid hormone. Diagnosis is made on the basis of clinical signs and history, palpation and blood tests. The thyroid gland regulates many organ systems in the body, so when it begins to produce too much hormone, multiple clinical signs can develop. Some of these signs include: Behaviour changes, weight loss despite a ravenous appetite, rapid heart rate or irregular rhythm, increased thirst and urination, vomiting, diarrhea and poor hair coat. If the hyperthyroidism is not treated, the cardiac disease that develops can result in death. Since the clinical signs are not specific for hyperthyroidism, a blood test is needed to confirm the presence of elevated T4 hormonal blood levels. Most cats that are affected are middle-aged and older and it is the most common endocrine disease diagnosed in this age bracket. Because these cats are older, it is advisable to perform complete blood screenings and some times other diagnostic test to make sure there is no other underlying disease processes present. Hyperthyroidism is caused by hyperplasia of the thyroid gland(s) in 99.9% of cats. Occasionally ectopic thyroid tissue (thyroid tissue found in other areas of the body besides the neck) is involved. Luckily, this disease is treatable and can be cured.
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WHY IODINE 131 (I131) IS THE TREATMENT OF CHOICE

Radioiodine

  1. Ninety five percent (95%) of our patients will be completely normal following a single treatment, never requiring further treatment or supplements for hyperthyroidism.
  2. I131 treatment is non-invasive - does not require surgery or anesthesia.
  3. I131 only destroys abnormal thyroid cells.
  4. I131 also targets abnormal ectopic thyroid cells (i.e., those located anywhere in the body).
  5. Eliminates the challenge and expense of daily medication.
  6. Cats will feel better within days after therapy and continue to improve for the next 2 to 3 months until normal (euthyroid) state is reached.
  7. I131 treatment costs are comparable to surgery/anesthesia performed at most facilities or approximately 18 months of tapazole/blood work treatment.

The isotope used for the treatment is iodine 131 (I131). I131 concentrates within thyroid tissue in the same manner as stable iodine. I131 preferentially localizes thyroid state (i.e., neoplastic or hyperplastic cells in the thyroid gland or anywhere else in the body), thus sparing the uninvolved normal thyroid cells.
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ADMISSIONS REQUIREMENTS

Candidates for radioiodine treatment should be relatively stable. Cats that have significant cardiovascular, renal, endocrine (e.g. diabetes mellitus), gastrointestinal or neurological disease are not considered good candidates for therapy until these conditions are stabilized. These cats may be referred for radioactive treatment once these conditions are stabilized by the referring veterinarian.

The following diagnostic tests are required prior to referral. These tests should be performed as close to initiating radioiodine treatment as possible:

  1. Physical exam
  2. Complete blood count
  3. Chemistry panel *
  4. Thyroid panel *
  5. Thoracic radiographs **

* A renal panel (BUN and creatinine) should be performed within one week of treatment, after being on tapazole for at least one week. A T4 level should also be repeated at this time. The reason for these precautionary measures is be assure that renal function will not be compromised in the absence of excess thyroid hormone.

**Thoracic radiographs are suggested as a pre-treatment screening measure to rule out any occult thoracic disease. If a heart murmur or arrhythmia is present on ecocardiogram and thoracic radiographs are required. If cardiac medication is necessary the cat must be on such medication for at least a week prior to treatment and owners should bring the medication with them.
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HOW LONG WILL MY CAT BE IN THE HOSPITAL?

I 131 is a radioactive substance that is excreted through the urine and feces. Radiation safety requirements dictate that cats treated with I 131 must be housed in a state licensed isolation ward where contact with humans is minimized and their radioactive hazardous waste can be contained. Once publicly safe radiation levels are reached, cats will be released. The shortest stay has been 7 days, the longest 15 days and the average stay is 12 days.

The cats treated at VRSR will have comfortable cages. Bedding, food and litter will be provided. Any special dietary needs or medications must be provided by the owner. Special toys and bedding may be provided by the owner, but must be disposed of as radioactive waste at the end of the treatment. Trained personnel will monitor all patients regularly throughout the day and night. Owners will be able to visit their cat by appointment, although they will only be able to view them through a special leaded window in the isolation area. If a medical or surgical emergency should arise while the cat is boarding, Veterinary Radiological Specialists of the Rockies (VRSR) has arranged with the Colorado Veterinary Specialists to handle daytime emergencies, and Animal ER to handle evening emergencies. Additional costs will be incurred if these emergency services are required.
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