Feline hyperthyroidism is the most common hormonal disorder of older cats, causing chronic weight loss, cardiovascular strain, and systemic effects that significantly reduce quality of life if untreated.
The welfare trajectory of feline hyperthyroidism is stark: untreated cats experience progressive weight loss, cardiovascular deterioration, hypertension-related blindness, and systemic organ damage over months to years. The disease is often gradual enough that owners attribute early signs to normal ageing, delaying diagnosis. Once treated, most cats recover well and enjoy significantly improved quality of life. The main welfare challenge is treatment access — daily medication requires owner compliance over years, and radioactive iodine, while curative, is expensive and requires a period of isolation from owners post-treatment. Dietary management with iodine-restricted food is an option for some cats but requires strict adherence. Early diagnosis through routine senior wellness checks remains the most important welfare intervention.