Hyperthyroidism is the most common endocrine disorder in cats over 10 years of age. It causes significant suffering through weight loss, cardiovascular effects, and anxiety, but responds well to treatment when diagnosed promptly.
Untreated hyperthyroid cats experience chronic distress from accelerated metabolism, cardiovascular disease, hypertension, and anxiety. The hypermetabolic state causes progressive muscle wasting despite a ravenous appetite. Secondary hypertension causes retinal detachment and blindness if uncontrolled. Anxiety and restlessness impair sleep and normal resting behaviour. Because the signs develop gradually and owners often attribute them to normal ageing, many cats suffer for months before diagnosis. Regular veterinary examination of older cats is essential for early detection.