Hyperthyroidism caused by benign thyroid tumours affects approximately 10% of cats over 10 years old. It is highly treatable, but untreated disease causes progressive deterioration in quality of life and secondary organ damage.
Untreated hyperthyroidism causes significant and progressive suffering. The hypermetabolic state creates a sensation of internal agitation — affected cats are often restless, vocalise excessively, and cannot settle. Weight loss continues despite ravenous hunger. Secondary cardiac and hypertensive complications, if unmanaged, cause pain and organ failure. Because signs develop gradually, owners may attribute them to normal ageing rather than treatable disease. Annual T4 screening for cats over 10 years is highly effective at early diagnosis when treatment is most straightforward. Most hyperthyroid cats treated with radioactive iodine or medication show dramatic improvement in demeanour, weight, and overall quality of life within weeks.