Hyperthyroidism is the most common hormonal disease of older cats, causing significant suffering if untreated. Effective treatments exist but many cats go undiagnosed for extended periods while experiencing poor welfare.
Hyperthyroid cats experience a state of chronic physiological stress — elevated heart rate, muscle wasting, gastrointestinal distress, and hypertension — that profoundly affects quality of life. Because increased appetite and apparent energy can seem like positive signs, owners sometimes miss or delay diagnosis. Annual blood screening for cats over age 10 catches the disease earlier, enabling treatment before secondary complications develop. The dramatic welfare improvement seen after successful treatment underscores how much these cats were suffering before diagnosis.