Hyperthyroidism in Cats: Managing a Common Endocrine Disease

Feline hyperthyroidism is the most common endocrine disorder in older cats. Early diagnosis and treatment prevent significant suffering and extend quality of life substantially.

Key Facts

Hyperthyroidism affects approximately 10% of cats over 10 years of age
It is caused by benign thyroid tumor(s) producing excess thyroid hormone
Signs include weight loss despite increased appetite, hyperactivity, vomiting, and increased vocalization
Untreated hyperthyroidism causes cardiac disease, hypertension, and kidney complications
Treatment options include radioactive iodine (curative), anti-thyroid medication, surgery, and dietary management
Radioactive iodine therapy is curative in over 95% of cases with a single treatment

Welfare Considerations

Untreated hyperthyroidism causes significant suffering through weight loss and muscle wasting despite voracious appetite, cardiovascular strain with secondary hypertension causing retinal detachment and blindness, and the discomfort of sustained elevated metabolism. Many owners initially misinterpret the behavioral changes as normal aging. Treatment dramatically reverses symptoms and improves quality of life. Anti-thyroid medication requires twice-daily dosing and regular monitoring but is effective when compliance is maintained. Radioactive iodine, where available, provides the best long-term welfare outcome through a single curative treatment.

What You Can Do

Include thyroid testing in annual health checks for cats over 8 years
Seek veterinary diagnosis promptly if your senior cat loses weight despite eating well
Consider radioactive iodine treatment for definitive cure if accessible
Monitor blood pressure in hyperthyroid cats — hypertension requires separate management
Administer anti-thyroid medication consistently if using medical management