Treatment Options:

Once hyperthyroidism is diagnosed, there are several treatment options you may consider:

• Medication

• Thyroidectomy (surgical removal of the thyroid)

• Radioactive Iodine therapy (I-131)

Out of the three options, the safest and most effective, is typically considered to be radioactive iodine therapy.

I-131 is injected into the cat subcutaneously. It is then absorbed throughout the body, including the thyroid gland, where the beta particles attack and destroy the overactive thyroid tissue.  The normal thyroid tissue remains unharmed. Over several months following therapy, the thyroid generally returns to normal function.

Benefits of I-131 Therapy:

I-131 therapy offers a highly effective and safe treatment for hyperthyroidism in cats:

• High Success Rate: Studies have shown I-131 is over 95% effective in curing hyperthyroidism in cats.

• Minimally Invasive: This procedure doesn't require anesthesia, making it suitable for compromised cats, and avoids surgical risks.

• Preserves Healthy Tissue: I-131 targets overactive thyroid cells, minimizing damage to healthy tissue.

• Rare Side Effects: Harmful side effects are uncommon with I-131 therapy.

• Cost-Effective: Compared to other treatments, I-131 can be the most cost-effective option in the long run.

• Eliminates Daily Medication: No more need for daily medication administration.

• Fast-Acting: Results are typically noticeable within a month.

• Veterinarian-Recommended: Many veterinary endocrinologists recommend I-131 therapy for suitable candidates.

Advantages Over Other Medications:

While medications like methimazole are safe for many cats, I-131 offers several advantages:

• Reduced Side Effects: Methimazole can have side effects like decreased gastrointestinal absorption, potentially impacting treatment effectiveness.

• Liver Concerns Minimized: Liver disease is a rare but potential concern with methimazole, which I-131 avoids.

Overall, I-131 therapy is often the preferred and safest option for treating feline hyperthyroidism.

Considering I-131 for your cat:

Before your cat undergoes I-131 therapy, please review the following protocol:

1. Pre-Treatment evaluation:
   Within 30 days of therapy, your veterinarian must perform a physical examination, complete blood count (CBC), general health chemistry profile, and thyroid level test (T4 and T3). Chest radiographs and urinalysis, especially specific gravity, are also highly recommended.
   
   Your veterinarian should perform any further diagnostics deemed necessary, such as ECG, thoracic, and abdominal ultrasounds. If your cat has been on methimazole for longer than 90 days, discontinue the medication at least 7 days before I-131 therapy. Have their thyroid levels checked again 7 days after stopping the medication. Please contact our facility or your veterinarian for a list of medications that may interfere with I-131 therapy.

2. Admission and Hospitalization:
   Upon arrival, your cat will be hospitalized in our nuclear medicine ward, separate from other animals.

3. Thyroid Scan (Optional):
   The day after admission, we may perform a thyroid scan (upon request at time of scheduling appointment) using a radioactive isotope called Tc99. This scan measures your cat's thyroid gland activity and helps us determine the appropriate I-131 dose. If you decline the scan, your cat will receive the standard dose.

4. I-131 Treatment:
   Your cat will receive a single dose of I-131 via a simple subcutaneous injection, which is quick and virtually painless. Hospitalization typically lasts 7-10 days, although state regulations require patients to fall below a certain radiation level before discharge. This means the length of stay can vary.

5. Monitoring and Communication:
   Our team of doctors and veterinary technicians will assess your cat daily throughout their stay. Their radioactivity levels will be monitored to determine when they can be safely discharged. While you can contact us for updates, visiting is not permitted due to radiation safety regulations. By law, your cat cannot be discharged until their radiation levels decrease sufficiently.

6. Discharge Instructions and Follow-Up Care:
   Upon discharge, you will receive detailed instructions and guidelines for the first 80 days your cat is home. Your veterinarian will also receive medical records to aid in post-treatment monitoring. Regular (every 6 months) examinations and diagnostics by your veterinarian are crucial to monitor for any hyperthyroidism-related health issues. Follow-up blood work will likely be recommended. In rare cases, cats may remain hyperthyroid or develop hypothyroidism after treatment, requiring additional medication and treatment.

7. Post-Treatment Precautions (Home):
   For the first 80 days after discharge, we recommend minimizing contact between your cat and anyone, especially children and pregnant women, to avoid radiation exposure. Additionally, please store your cat's litter for 80 days before it can be discarded according to your state laws and regulations. .

Our compassionate staff represents years of nuclear medicine experience and feline care.  We can promise that your cat will be in good hands at the Myhre Equine Clinic / New England Regional Veterinary Imaging Center.

References:

http://www.academic-server.cvm.umn/radiology/I131

http://www.cah.com/dr_library/hyperthyr.html http://www.catspecialist.com

http://www.radiocat.com/section4.html

http://www.southpaws.com/I-131.html

Researched and written by Joshua VanHoose and Diane Sickles, veterinary technicians at the Myhre Equine Clinic and New England Regional Veterinary Imaging Center.