Hyperthyroidism is the most common endocrine disorder in middle-aged and older cats, causing significant welfare compromise through weight loss, cardiovascular effects, and behavioural changes.
Untreated hyperthyroidism causes progressive and significant welfare compromise. Cats suffer from chronic weight loss despite ravenous appetite, cardiovascular stress, hypertension, and secondary organ damage. Restlessness and hyperactivity impair normal resting behaviour. Early diagnosis and treatment dramatically improves welfare — most cats show rapid clinical improvement after treatment initiation. Radioactive iodine offers permanent cure with minimal ongoing welfare burden. Methimazole management requires regular blood monitoring but provides effective long-term control for cats unsuitable for curative treatment.