Feline hyperthyroidism is the most common hormonal disorder in older cats and causes significant welfare suffering when undiagnosed or inadequately treated. Improved recognition and management can dramatically improve quality of life for affected cats.
Feline hyperthyroidism causes a sustained welfare burden through its metabolic effects on multiple organ systems. Affected cats experience a state of chronic physiological overdrive: elevated heart rate, hypertension causing retinal damage and strokes, muscle wasting from protein catabolism, and gastrointestinal disturbance. The weight loss and voracious appetite are often misinterpreted by owners as signs of a healthy, food-motivated cat — a critical diagnostic error that delays treatment. Hypertensive retinal detachment — causing sudden blindness — is a preventable welfare disaster that occurs when hyperthyroidism goes undiagnosed. Diagnosis requires a simple blood test (total T4 serum concentration) that should be routine in annual check-ups for cats over eight years old. Treatment dramatically improves quality of life within weeks; the choice of treatment modality should be guided by patient factors, owner circumstances, and accessibility of radioactive iodine facilities.