What is Hyperthyroidism?
Hyperthyroidism is one of the most common hormonal conditions in older cats. It happens when the thyroid gland (in the neck) produces too much thyroid hormone. This hormone controls metabolism — so when there’s too much, the body speeds up.
Over time, the overactive thyroid puts stress on the heart, kidneys, and other organs, which is why early detection and treatment are so important.
Common Signs of Hyperthyroidism
Cats with hyperthyroidism often show one or more of these signs:
- Weight loss despite a great appetite
- Increased thirst and urination
- Vomiting or diarrhea
- Hyperactivity or restlessness
- Poor coat quality, greasy or unkempt fur
- Rapid heartbeat or heart murmur
- High blood pressure
- Occasionally, sudden blindness from retinal detachment (if untreated)
How We Diagnose It
Diagnosis is made through bloodwork measuring thyroid hormone (T4) levels.
- A high T4 confirms hyperthyroidism.
- Sometimes additional tests (like free T4 or TSH) are run for borderline results.
- We often check kidney values and blood pressure at the same time since these organs are closely linked to thyroid function.
Treatment Options
There are several ways to manage hyperthyroidism:
- Medication (Methimazole)
- Given daily by mouth or as a transdermal gel.
- Controls, but doesn’t cure, the disease.
- Requires regular monitoring.
- Prescription Diet (Hill’s y/d)
- Very low in iodine, which the thyroid needs to produce hormone.
- Works best if your cat eats only this diet — no other food or treats.
- Radioactive Iodine Therapy (I-131)
- A one-time treatment that cures most cats.
- Safely destroys the overactive thyroid tissue without harming other organs.
- Surgery (Thyroidectomy)
- Removes the affected thyroid gland.
- Usually reserved for specific cases or when other options aren’t available.
Monitoring & Follow-Up
After treatment starts, we’ll recheck your cat’s thyroid level in 3–4 weeks. Once levels stabilize, rechecks are usually done every 6 months.
If on medication, we’ll also monitor kidney values and liver enzymes, since both can be affected by treatment or the disease itself.
Long-Term Outlook
With proper management, most cats live normal, happy lives for many years after diagnosis. Hyperthyroidism is highly treatable — the key is staying consistent with medication or diet and keeping up with regular monitoring.
Quick Summary
- Too much thyroid hormone speeds up the body’s metabolism.
- Symptoms: weight loss, increased appetite, hyperactivity, poor coat.
- Diagnosed by bloodwork (T4 level).
- Treated with medication, diet, radioactive iodine, or surgery.
- Regular monitoring keeps your cat healthy long-term.
If you have any additional questions, please call us at 319-277-7675 or email us at [email protected]. We would be happy to assist you.