Hyperthyroidism is the most common endocrine disorder in middle-aged and older cats, causing significant physiological distress that is highly treatable once diagnosed — making early detection a welfare priority.
Hyperthyroid cats experience a state of chronic physiological overdrive — elevated heart rate, hypertension, and metabolic acceleration create a subjective experience likely characterized by anxiety, restlessness, and physical discomfort. Weight loss despite eating represents the body consuming itself to fuel the elevated metabolic rate. The hypertensive complications — retinal detachment causing blindness, hypertensive encephalopathy, and cardiac hypertrophy — represent serious welfare harms that develop over months of untreated disease. Treatment transforms the welfare of affected cats dramatically: radioactive iodine provides cure, returning most cats to normal physiological baseline. The challenge is that early signs are sometimes misread as the cat simply being more active or eating well, delaying diagnosis. Annual thyroid screening from age 8 enables early detection.