Hyperthyroidism is the most common endocrine disease in older cats, causing weight loss, hyperactivity, and cardiac disease if untreated. Multiple effective treatments allow excellent welfare outcomes.
Hyperthyroid cats experience a metabolic state that causes chronic discomfort including restlessness, hunger despite eating, increased blood pressure causing headaches and visual disturbances, and progressive heart disease. Owners sometimes perceive the increased energy and appetite as signs of good health, delaying diagnosis and treatment. The condition is progressive — cardiac hypertrophy from thyroid hormone overstimulation can progress to congestive heart failure and acute respiratory distress. Successful treatment with methimazole dramatically improves quality of life within weeks. Radioactive iodine offers permanent cure. Dietary management using iodine-restricted food requires strict feeding protocols. Early diagnosis and treatment prevents significant welfare harm from progressive cardiac disease and associated suffering.