Cat Hyperthyroidism: Welfare and Treatment

Hyperthyroidism is the most common endocrine disease of older cats, causing significant systemic illness that responds well to treatment, dramatically improving welfare.

Key Facts

Hyperthyroidism affects approximately 10% of cats over ten years of age.
It is caused by benign thyroid tumours producing excess thyroxine, accelerating metabolism.
Signs include weight loss despite increased appetite, hyperactivity, vomiting, and unkempt coat.
Untreated hyperthyroidism causes hypertension, heart disease, and kidney damage.
Treatment options include daily medication, radioactive iodine, surgery, or dietary iodine restriction.

Welfare Considerations

Hyperthyroid cats experience significant systemic distress from accelerated metabolism — weight loss, cardiac stress, hypertension, and GI disease. The condition is frequently missed because increased appetite and apparent energy mask underlying illness in early stages. Treatment response is excellent: most cats show dramatic improvement in quality of life within weeks. Treatment choice should consider the individual cat's temperament, owner circumstances, and concurrent health conditions including renal function which may worsen after thyroid normalisation.

What You Can Do

Test thyroid function annually in cats over ten years of age as part of senior health screening.
Seek veterinary assessment promptly if your cat loses weight despite eating well.
Discuss all four treatment options with your vet to choose the best fit for your cat.
Monitor renal function after treatment initiation as kidney disease can unmask after thyroid correction.
Maintain regular follow-up monitoring to ensure thyroid levels remain within the target range.