Hyperthyroidism is the most common hormonal disorder in older cats. With several effective treatment options available, quality of life can be excellent after diagnosis and treatment.
Feline hyperthyroidism causes significant welfare impact through weight loss, cardiovascular stress, hypertension, and the psychological effects of hyperactivity and GI distress. Cats with untreated hyperthyroidism often appear deceptively "fine" in early stages — increased energy can be mistaken for healthy vitality — while progressive organ damage accumulates. The welfare opportunity is substantial: treatment is highly effective and can restore cats to excellent quality of life for many additional years. Radioactive iodine treatment, while requiring brief isolation, offers permanent cure without ongoing medication burden. Daily medication (methimazole) is effective but requires consistent administration and monitoring. Early detection through regular blood testing of cats over age 10 prevents unnecessary suffering from untreated disease.