Hyperthyroidism is the most common endocrine disorder of older cats and offers multiple treatment pathways with different quality-of-life implications.
Untreated hyperthyroidism causes chronic metabolic stress — cats are in a state of constant physiological overdrive, losing weight despite eating voraciously, and potentially suffering from hypertension-related complications including retinal damage and cardiac effects. Treatment dramatically improves welfare for most cats. Radioactive iodine offers the best long-term outcome but requires a period of isolation that can be stressful. Daily medication is effective but compliance-dependent and may cause side effects. Dietary iodine restriction requires strict feeding management. The unmasking of kidney disease after treatment requires careful monitoring — some cats with borderline renal function deteriorate after thyroid treatment and need renal support.