Hyperthyroidism is the most common endocrine disorder in older cats, and untreated disease causes chronic suffering that is often mistaken for normal aging by owners.
Hyperthyroidism imposes chronic welfare costs that are often invisible to owners who interpret the signs as aging rather than disease. A hyperthyroid cat is not simply thin and active for its age — it is experiencing a relentlessly elevated metabolic rate that causes a state analogous to chronic anxiety, with elevated heart rate, gastrointestinal disturbance, and muscle wasting. The cardiac consequences develop silently and can become irreversible if untreated. The welfare tragedy is that treatment is highly effective and transforms affected cats — post-treatment behavioral improvement is often remarkable. The barrier is diagnosis: owners and sometimes veterinarians attribute signs to age. Annual thyroid hormone testing in cats over 10 years old is a high-impact welfare intervention that catches disease before cardiac damage accumulates.