Hyperthyroidism is the most common hormonal disease in older cats, causing significant welfare harm that responds well to appropriate treatment.
Hyperthyroid cats experience a complex state of welfare compromise — elevated thyroid hormone simultaneously increases metabolic rate, causing weight loss despite ravenous appetite, cardiovascular stress, hypertension, and hyperactivity that is not normal alertness but physiological agitation. Owners often misinterpret the early signs as positive aging — the cat seems more active and is eating well — delaying diagnosis. As the condition progresses, cardiac complications including hypertrophic cardiomyopathy cause additional welfare harm. All available treatment options are effective when applied appropriately, and most cats treated for hyperthyroidism show rapid welfare improvement. Regular blood testing from age 10 enables early diagnosis.