Hyperthyroidism is the most common endocrine disorder of older cats, causing significant physical suffering if untreated and requiring careful lifelong management.
Unmanaged feline hyperthyroidism causes progressive suffering. The metabolic acceleration leads to muscle wasting despite high food intake — cats feel chronically hungry and yet lose body condition. Gastrointestinal symptoms (vomiting, diarrhea) are distressing and painful. Cardiac hypertrophy from chronic hyperthyroidism can lead to heart failure if untreated. Hypertensive retinopathy may cause sudden blindness — a traumatic event with major welfare implications. Because the disease onset is gradual, owners sometimes attribute early signs to "normal aging," delaying diagnosis and treatment. Early identification and treatment dramatically reduces suffering and extends quality life years.