Cat Hyperthyroidism: Welfare Management in Senior Cats

Hyperthyroidism is the most common endocrine disease of older cats, causing significant welfare impacts if untreated.

Key Facts

Hyperthyroidism affects approximately 10% of cats over 10 years of age
A benign thyroid tumour (adenoma) is the cause in over 95% of cases
Signs include weight loss despite increased appetite, hyperactivity, vomiting, diarrhoea, and heart disease
Treatment options include medication (methimazole), radioactive iodine, surgery, and dietary iodine restriction
Radioactive iodine is curative in over 95% of cases and is considered the gold standard treatment
Concurrent kidney disease may be unmasked after treatment — monitoring renal function is essential

Welfare Considerations

Untreated hyperthyroidism causes sustained physiological stress — elevated heart rate, hypertension, weight loss despite hyperphagia, and gastrointestinal disruption — that significantly impairs quality of life. Cats often appear superficially well because their appetite and activity are maintained, delaying diagnosis. Welfare-centred care involves annual thyroid screening for cats over 9 years, prompt treatment when diagnosed, and ongoing monitoring for treatment side effects and concurrent conditions. Methimazole provides effective control but requires lifelong administration; radioactive iodine offers a one-time curative option that, where accessible, provides the best long-term welfare outcome.

What You Can Do

Request annual thyroid screening for cats over 9 years of age
Seek veterinary assessment if your cat loses weight despite eating well
Discuss radioactive iodine treatment with your vet if your cat is a suitable candidate
Monitor kidney function after initiating hyperthyroid treatment as directed by your vet
Ensure ongoing monitoring — thyroid levels should be checked every 3-6 months on medication