Hyperthyroidism is the most common endocrine disorder in older cats, causing significant welfare impact if untreated but responding well to treatment.
Untreated hyperthyroidism causes progressive weight loss, cardiac complications, and hypertension that can lead to blindness and kidney disease. Affected cats are often restless, irritable, and vocalise excessively. Medical management with methimazole controls the condition effectively but requires lifelong twice-daily administration. Radioactive iodine treatment is curative but requires a period of isolation after administration. Regular monitoring of thyroid levels and kidney function is essential. Treatment significantly improves welfare and quality of life in affected cats.