Feline hyperthyroidism is the most common endocrine disorder in older cats, affecting around 10% of cats over 10 years old. Understanding treatment options and welfare implications helps owners provide optimal care.
Feline hyperthyroidism causes significant welfare compromise through its symptoms and its secondary effects on cardiovascular and renal health. Cats lose muscle mass and body condition despite eating voraciously — owners sometimes misinterpret this as healthy appetite. Cardiac hypertrophy from excess thyroid hormone can lead to heart failure and thromboembolism (blood clots causing sudden pain and paralysis). Hypertension causes retinal detachment and blindness. Once diagnosed, treatment dramatically improves welfare: methimazole controls symptoms effectively but requires lifelong daily administration (resisted by many cats). Radioactive iodine offers a permanent cure with minimal stress and no long-term medication, though it requires a period of isolation post-treatment. Surgical thyroidectomy is effective but carries anesthetic risk in older cats. Iodine-restricted prescription diets are convenient but must be fed exclusively to be effective.