Hyperthyroidism is the most common hormonal disorder in older cats. Without treatment it causes significant suffering, but well-managed cases can enjoy good quality of life.
Hyperthyroidism creates a paradoxical presentation that can mislead owners: cats with this condition may appear hyperactive and eat voraciously, masking the severe internal suffering of elevated heart rate, hypertension, and progressive weight loss despite apparent hunger. Many owners attribute the signs to normal aging. Untreated hyperthyroidism causes progressive cardiac damage, chronic hypertension, blindness from retinal detachment, and eventually heart failure. The welfare stakes of early diagnosis and treatment are very high. Routine thyroid screening for cats over 10 is among the most impactful geriatric preventive care interventions available, with well-managed cats often achieving complete remission through radioactive iodine.