Treating of Hyperthyroidism

Hyperthyroidism is the most common hormone based disease in cats. It is characterized by the overproduction of thyroid hormone and a subsequent increase of metabolic rate in your cat. During this disease the thyroid gland sometimes enlarges, but less than 2 percent of these growths involve malignant thyroid gland tumors.
Hyperthyroidism is a multi-systemic disease process. Many important organ systems can be effected and symptoms may change during the disease process. Those organ systems which are frequently targeted include; the heart, lungs, kidneys, blood pressure regulation and the skeletal muscle system.

Dr. Paul Howard, of the Veterinary Emergency and Specialty Center (VESC), is licensed in radioactive iodine treatment, and began providing the service in April of 2003. I-131 is considered the treatment of choice for most affected felines. The VESC is one of a limited number of hospitals nationwide to offer this alternative.

Your primary veterinarian will perform pretreatment evaluations to determine whether I-131 is a reasonable alternative for your cat. If your companion is determined to be a good treatment candidate, you will be allowed to schedule a hospitalization stay of approximately five days.  Daily progress reports from the Veterinary Emergency and Specialty Center are available through the nursing staff.

Since less than 2% of hyperthyroid cats have cancerous growths, treatment is usually very successful.

Several tests may be needed to identify the best choice for your friend.

1. Radioactive Iodine Therapy
A very effective way to treat hyperthyroidism. It is administered by a single injection of radioactive iodine (I-131) by a veterinarian specifically licensed to administer radioactive isotopes and is considered by most authorities to be the treatment of choice.

2. Surgery
Surgical removal of the thyroid nodules can also be a very effective cure, if the disease is restricted to one easily accessible thyroid gland. Statistically, 70% of patients have nodules in both glands and may, therefore, require multiple surgical procedures. Anesthetic, operative and postoperative complications are also a significant concern in these patients.

3. Oral Medication
Daily administration of an oral drug, methimazole, is another option. With this option, the abnormal tissue is not destroyed, but rather prevented from producing excess thyroid hormone.

Dr. Howard and the staff at the VESC feel privileged to offer this safe, effective, and convenient treatment to the cat families of the central Virginia region.

Letter from Dr. Howard

Your primary care veterinarian has provided this information packet to acquaint you with radioactive iodine (I-131) therapy as a treatment option for feline hyperthyroidism.  Although other forms of treatment are available (daily medication for the rest of your pet’s life, a prescription diet and attempted surgical removal of abnormal thyroid tissue), I-131 is generally considered the “Gold Standard” by experts in the field of veterinary endocrinopathies (hormone based diseases).

I-131 therapy is safe and effective, results in a cure for most felines and is best utilized early in the disease process.  Alternative forms of therapy generally attempt to “control” the symptoms of hyperthyroidism but do not offer a realistic expectation of curing the disease. While the dose of I-131 is very small compared to doses used for similar conditions in human medicine, some simple post treatment modifications in social interactions and litter disposal are necessary.

I-131 is administered by single injection like a routine vaccination.  Little to no side effects are expected and improvements are generally noted within one month of administration.  Treated patients are required by federal and state regulations to stay in the hospital for 2-4 days post treatment.

Our program is designed to provide individualized attention and treatment for your feline friend.  A one hour “screening” consultation prior to treatment is scheduled and gives us the opportunity to discuss treatment options, establish goals and develop a plan tailored to your specific circumstances.  In addition to evaluation of hyperthyroidism, routine laboratory and radiographic examinations (x rays) provided by your primary care veterinarian are evaluated during this consultation so that other significant health concerns can be identified and discussed.

While most patients referred for I-131 therapy are good candidates, there may be specific medical concerns with individual patients which warrant further investigation or consideration of alternative therapies.  In this event, we will continue to work closely with your primary care veterinarian to develop a specific plan to address your specific needs.

Screening consultations can be scheduled by calling the hospital (804-353-900) and requesting to speak with the “referral coordinator”.  Referral coordinators are available Monday-Friday from 8AM until 5 PM.  The screening consultation is scheduled for up to one hour and costs $50.  The cost for further testing done in conjunction with the screening consultation at the hospital and cost of I-131 treatment will be discussed during the screening consultation.

Dr. Paul Howard

What to Expect with Radioactive Iodine Therapy and Frequently Asked Question

What does the treatment involve?

  • Physical examination prior to treatment
  • Evaluation of all diagnostic tests provided by your primary care veterinarian. Administration of I-131 – by injection similar to a routine vaccination!
  • Daily care and monitoring of radiation levels.
  • Follow up telephone consultation with your primary care veterinarian as needed to evaluate post treatment status.

Will my cat experience any side effects?

  • No direct side effects from administration are expected. As the radioactivity destroys the abnormal thyroid tissue, there may be mild changes in individual patient behaviors but your cat should not experience any significant undesirable changes.

When can my cat come home?

  • Length of hospitalization is 2-4 days after treatment. Patients are admitted by 6pm on Sunday evening, treated on Monday morning and discharged 2-4 days after treatment. We will monitor your cat’s radiation levels during his/her stay with us. Release is determined by compliance with federal and state regulations which define the “safe” level of residual radioactivity at which a patient can be discharged. As required by these regulations, please remember to bring your cat in a carrier for drop-off and pick-up.

What is the quality of care my cat will receive during his/her stay?

  • Experienced licensed veterinary technicians lovingly care for our I-131 patients. Your cat will be in a comfortable and relaxed atmosphere away from noise and dogs. We obtain specific information from the owners regarding favorite foods (including special treats), sleeping habits, and personal behaviors.

Can I visit my cat during his/her stay?

  • Unfortunately state and federal regulations currently limit access to the areas where patients recently treated with radioactive iodine are maintained to trained hospital personnel. Our technicians are thoroughly trained in working with radiation and must work under strict guidelines for their own protection.

How will I find out how my cat is doing?

  • You can call any time to receive an update from a technician or referral coordinator.

Will there be any follow up visits with I-131?

  • There are no follow up visits required at the VESC. Follow up visits to your primary care veterinarian are recommended one, three, six, and twelve months after treatment to monitor both the thyroid hormone levels and your cat’s general health. The results of these tests are forwarded to the VESC for evaluation and consultation as needed.

How does Radioiodine (I-131) Therapy work?

  • Feline hyperthyroidism is caused by spontaneously occurring thyroid masses. Approximately 98% of these nodules are benign (called adenoma) and the condition frequently (70%) involves both lobes of the thyroid gland. Fortunately, the incidence of thyroid malignancy (carcinoma) is rare (1-2%). Both thyroid conditions are treatable with radioactive iodine (I-131); however the dose administered and the desired results of therapy are different. The goal in treating benign disease is to selectively destroy the abnormally functioning cells and spare the rest of the thyroid gland. Ideally this should result in normal thyroid hormone levels and correction of weight loss and the other clinical signs. Usually, there is no need for daily thyroid medication after I-131 treatment. The goal in treating the much rarer, thyroid adenocarcinoma is to destroy all the thyroid tissue. After treatment, these patients will need daily thyroid supplementation for life.
  • I-131 is a radioactive form of iodine. Iodine is needed by thyroid cells to produce thyroid hormone. In a normal animal, thyroid hormone levels are controlled by a system similar to our household thermostat. When enough thyroid hormone is present (similar to enough heat being in your house), the system automatically shuts off. In hyperthyroid cats, the system fails to shut off and too much thyroid hormone is produced. When radioactive iodine is administered to these individuals, the cells that fail to shut off are killed by the radioactivity while the normal cells (which are shut off) are protected.

What is the success rate?

  • The success rate of I-131 is approximately 85-95%. A few patients may require an additional treatment with I-131 if they do not return to normal thyroid function within 3-6 months. For unknown reasons a small percentage of cats will become hypothyroid (do not produce enough thyroid hormone) after treatment. If this occurs it may be a temporary problem and require no medical intervention. In rare cases of permanent hypothyroidism, cats may require a daily supplement to maintain normal thyroid hormone levels.

Bloodwork and Test Provided by your referring veterinarian

Laboratory test and x-rays within THIRTY DAYS of the treatment date.

Thyroid hormone level (T4) Laboratory Analysis required are:

  • CBC with differential (complete Blood Count)
  • Complete Biochemical Profile
  • T4 (Thyroid level)
  • Urinalysis with sediment
  • Retrovirus testing for FeLV and FIV
  • Results of additional laboratory tests if indicated by individual patient profile

Imaging Studies:

  • Two view thoracic and abdominal radiographs
  • Results and interpretation of cardiac and abdominal ultrasound examination if indicated by individual patient profile.

Before the Treatment

Careful screening for other disease conditions will be completed before being admitted for radioactive treatment. The screening will consist of bloodwork, urinalysis, radiographs, and possibly additional test such as ultrasound of the heart or abdomen.

Dr. Howard must examine your cat before the scheduled admission date. At that time, or shortly thereafter, it will be determined if your cat is a suitable candidate for I-131 treatment.

If your cat is on antithyroid medication such as Tapazole (methimazole), please discontinue at least one week before your cat’s scheduled admission date for treatment. Discontinuing medication will increase the chances of a successful treatment.

TREATMENT DAY: Please Bring: ***Six day supply of regular food*** ***Please bring your cat in a carrier (required)***

Safety Precautions Following I-131 Therapy 

The present level of radioactivity is such that it will be necessary for you to alter your social interactions and possibly alter litter box routines for the next three weeks. Following these instructions will ensure that the radiation doses that you and your family member might receive are extremely small.

Your cat’s waste products will contain radioactive substances for the first 3 weeks after discharge, necessitating strict litter disposal requirments. Preferentially, use flushable, scoopable litter and simply flush soiled litter 2-3 times daily. The litter box should be placed in a room not typically occupied by family members for extended periods. A spare bathroom or bedroom is ideal. If you are unable or are unwilling to flush soiled litter, place all soiled litter in a designated, rigid trash container that has been doubled lined with heavy duty plastic bags. Place the container in an infrequentley used area of the house, outside or garage. At the end of the three week collection period, secure the top of the plastic bags (tape, zip tie), place a lid on the receptacle and store for three months prior to disposal in regular trash.

Wear examination gloves when changing or disposing of soiled litter.

Do not allow young children to change the litter.

Prohibit contact between pregnant women and the cat or its waste products.

Limit your cats activity to a single room of the house such as a spare bedroom for the first 7 days after discharge. If confinement is not possible, minimize and when reasonably possible eliminate being in the same room for more than a few minutes. After the first week, avoid close and prolonged contact for an additional two weeks. You should feel free to shower some affection on your pet, but do not cuddle for lengthy periods of time.

Wash your hands after petting or handling your cat. Be particularly vigilant about having your children frequently wash their hands when they are home with the cat.

Do not let your cat run free outdoors for the next three weeks.

Do your best to keep your cat out of your kitchen, especially when food is being prepared or consumed. Do not panic if he/she manages to gain entrance to the kitchen, but do a good job of cleaning surfaces which could come in contact with food.

After the initial twenty-one 3 week period, you can dispose of litter as you normally would, as your cat’s waste products no longer contain significant amounts of radioactive iodine. Normal social interactions with your cat can also be resumed at this time. However, any surface contaminated by your cat’s waste products during the first 21 days should be considered potentially radioactive. All potentially contaminated material (litter box, gloves, any non-flushable waste) should be placed into a sealed plastic bag and should be stored in an infrequently used area of your house or garage for 3 months prior to disposal in regular trash or re-use.

Call the Veterinary Emergency & Specialty Center at 804-353-9000 to discuss any other radiation safety concerns.

It is imperative that you follow the restrictions as indicated for both your own safety and to avoid problems at your local trash processing facility. If you dispose of any contaminated litter in your trash can during the initial 3-week period, radiation monitors at the trash disposal facility will likely be activated. This has resulted in costly expenditures of labor for cities and towns necessitated by isolating and analyzing the radioactive materials. Should the radioactive trash be traced back to you it could result in substantial financial liability.

 I-131 Program Discharge Kit Information

The following is a list of supplies that you should obtain prior to your pet’s discharge. This will allow you to conform to the safety precautions as outlined in the document “Safety Precautions Following I-131 Therapy”.

1. Flushable, scoopable litter – check local pet supply stores for availability prior to release. Familiar brands include:

  • Worlds’ Best Litter
  • Arm & Hammer Easy Flush Litter
  • Cat’s Pride
  • Premium Choice Flushable
  • Our Cat’s Choice Cat Litter
  • Cat Country Organic Wheatgrass Litter
  • Swheat

Many other brands are available at various locations.

1. Rubber or Latex gloves – grocery store, drug store, home improvement store

2. Plastic litter box liners – 3 week supply (optional)

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