Hyperthyroidism affects the majority of older cats and is the most common endocrine disease in the species, with excellent welfare outcomes achievable through appropriate treatment.
Untreated hyperthyroid cats experience chronic weight loss despite ravenous appetite, hypertension causing retinal detachment and blindness, and cardiac hypertrophy. These welfare costs are entirely preventable with treatment. Radioactive iodine is curative but requires a short hospitalisation period. Daily methimazole requires owner compliance and regular monitoring but maintains excellent quality of life. Both approaches dramatically improve individual welfare when initiated promptly after diagnosis.