Feline hyperthyroidism is the most common endocrine disorder in older cats, causing progressive welfare deterioration that responds dramatically to appropriate treatment, making early detection critical.
Hyperthyroid cats experience a metabolic storm: despite eating voraciously, they lose muscle mass and body condition as their metabolism races uncontrollably. The associated hypertension can cause sudden blindness from retinal detachment, and cardiac hypertrophy can lead to heart failure. Many hyperthyroid cats are also anxious, restless, and unable to settle — signs that are sometimes attributed to age-related personality change. Untreated hyperthyroidism is progressive and ultimately fatal. Treatment produces a dramatic welfare improvement — weight stabilisation, calm demeanour, improved coat condition — that is frequently described by owners as transformative. The challenge is that improved kidney function post-treatment can unmask underlying chronic kidney disease.