Causes
Hyperthyroidism is a commonly diagnosed disease in cats age 7 and above, and is caused by an overproduction of hormone in the thyroid glands which are located in the neck.
Unfortunately, there are currently no known preventive measures for hyperthyroidism, except possibly ones based on diet. However, early diagnosis decreases the secondary problems and improves the prognosis.
Studies have shown that the best food for cats is canned or raw diets that contain little to no fruits, vegetables, gluten or grains. Try to avoid foods that contain high levels of Sodium Selenite, or Iodine (more commonly found in fish) as they have been linked to the disease.
Symptoms
• Weight loss despite a good or increased appetite.
• Muscle weakness and/or loss of balance.
• Increased appetite (polyphagia).
• Hyperactivity or restlessness.
• Increased thirst and urination (polydipsia/polyuria).
• Vomiting and/or diarrhea.
• Poor coat condition (unkempt, greasy, or matted fur).
• Rapid or irregular heart rate (tachycardia).
• Panting or difficulty breathing.
• Enlarged thyroid gland (palpable lump in the neck).
• Behavioral changes (aggression, irritability, or excessive vocalization).
Yowling, (especially at night) is also a pretty common symptom. Yowling is hard to describe, but you know it when you hear it! This disturbing sound is a combination of a yowl, a howl, and a whine. It is melodic and melodramatic. It’s persistent and it means, “Pay attention, something is wrong with me!”
Below is a 30 sec. audio clip of a cat yowling.
If any of the above symptoms present themselves, it's time to take your cat to the vet for blood work. The T4 blood test is typically the indicator for hyperthyroidism.
Bloodwork Summary Chart
I have prepared a "Bloodwork Summary Chart" that is available for download in two formats. This chart will help you keep track of the important blood tests during your visits to the vet.
Click here for the Excel version of the chart.
Click here for the PDF version of the chart.
I have also prepared a guide called "Common Blood Tests For Cats." This guide will help you identify the more commonly prescribed blood tests by your vet.
Click here for the PDF version of the guide.
Treatment
Oral and Transdermal Medication
The most common medication prescribed to treat hyperthyroidism is called Methimazole. This medication blocks the production of T4 and T3 hormones. A good 2 to 4 weeks are needed before thyroid blood tests will show the effect of the treatment.
Methimazole is given in one of two ways:
1 - Orally in tablet form, which is the most effective form. Rather than try to pill my cats, I find it easier to add about an 1/8" of water to a 10ml dosing syringe, and then drop the dose in. Let it sit for a few minutes till it's dissolved, then quickly squirt it in the side of their mouth.
2 - Transdermally inside the tip of the ear. Transdermal meds need to be compounded at a pharmacy.
NOTE: It's good to know that the more Methimazole you treat with, the lower your cat's T4 level. Consequently, the less Methimazole you treat with, the higher your cat's T4 level. This is important information, as your vet may need to adjust the dosage to achive the optimum T4 level in the blood test's normal reference range.
If your cat also has kidney disease, and especially if your cat is older, the vet will likely try to keep the T4 level near the lower end of the normal range for stages 1-3, but near the middle of the normal range for stage 4. This helps with the kidney's blood flow and also helps to strike a balance between the two diseases.
Radioactive Iodine Therapy (I-131)
This treatment avoids surgery, anesthesia, and anti-thyroid drugs. A single injection is given under the skin, and the radioactive iodine is quickly absorbed into the bloodstream. The majority of cats have normal hormone levels within a week or two of treatment.
Surgery (Thyroidectomy)
Removal of the thyroid gland is a surgical procedure with a good success rate. General anesthesia is used and there may be a risk for older cats. Heart, kidney or other problems may cause complications.