What is hyperthyroidism?

Hyperthyroidism is excess production of thyroid hormones, which increases the body’s metabolism. Most hyperthyroid cases are due to a benign tumor on the thyroid gland and, if left untreated, can negatively impact a cat's weight, blood pressure, heart, vision, liver, and kidneys.

What are common hyperthyroid signs in cats?

Early signs include:

• Unkempt appearance

• Increased appetite

• Restlessness or vocalization

• Lethargy, and rarely, poor appetite

Intermediate to advanced signs include:

• Weight loss 

• Increased thirst and urination

• Vomiting 

• Diarrhea

• Blindness

• Sudden death

How is hyperthyroidism managed in cats?

Hyperthyroidism management can involve various approaches. Radioactive iodine therapy can destroy the tumor, and is often curative. Surgery to remove the tumor is no longer routinely performed. Daily medication to inhibit thyroid production can be effective, but is lifelong, requires diligence, and regular diagnostic monitoring. A strict low-iodine prescription diet can also inhibit thyroid production, with varying results. Discussing a personalized management plan with your veterinarian is important for the best outcome for your cat. Regardless of the treatment plan chosen, regular veterinary visits and diagnostic testing are required to monitor treatment response. 

What is the prognosis for cats with hyperthyroidism?

The prognosis depends on your cat’s response to the chosen management plan. Overall, well-controlled hyperthyroid cats can have a good quality of life, and a normal lifespan, but some may eventually develop chronic kidney disease.  

Management tips for cats with hyperthyroidism  

At-home needs include:

• Easy access to food, water, and a clean litter box

• Consistency with any prescribed medications, which can be compounded for easier administration

• Strict adherence to a low-iodine prescription diet, if recommended by your veterinarian

• Monitoring appetite, drinking, urination, defecation, weight, and energy levels

In a crisis situation:

Contact your veterinarian immediately if your cat has uncontrollable vomiting or diarrhea, difficulty breathing or walking, is vocalizing in pain, or collapses.