Feline Hyperthyroidism: Welfare Management in Older Cats

Hyperthyroidism is the most common hormonal disorder in cats, primarily affecting those over 10 years old. Early diagnosis and treatment dramatically improve quality of life.

Key Facts

Feline hyperthyroidism is caused by a functional adenoma of the thyroid gland producing excess thyroid hormone.
The condition affects approximately 10% of cats over 10 years old, making it extremely common in geriatric cats.
Classic signs include weight loss despite increased appetite, hyperactivity, vomiting, increased thirst and urination, and poor coat condition.
Without treatment, hyperthyroidism causes cardiac complications including hypertrophic cardiomyopathy and hypertension.
Treatment options include daily medication (methimazole/carbimazole), radioiodine therapy (curative), surgery, or iodine-restricted diet.
Radioiodine therapy is highly effective and curative in approximately 95% of cases with a single treatment.
Concurrent chronic kidney disease must be considered, as treating hyperthyroidism can unmask pre-existing renal insufficiency.
With treatment, most hyperthyroid cats enjoy significantly improved quality of life and normal lifespan.

Welfare Considerations

Hyperthyroidism causes significant chronic suffering before diagnosis. The persistent high metabolic rate, cardiac strain, hypertension, and GI disturbances impair quality of life substantially. Cats with undiagnosed hyperthyroidism are often dismissed as "just getting older" when in fact they are experiencing a treatable condition. Many owners attribute the signs to normal ageing and do not seek veterinary attention until the disease is advanced. Screening older cats (annual thyroid checks from age 8 onwards) enables early diagnosis and treatment. With appropriate treatment, hyperthyroid cats typically show rapid improvement in body condition, behaviour, and general wellbeing, illustrating how veterinary intervention can meaningfully improve welfare outcomes.

What You Can Do

Schedule annual veterinary health checks including thyroid assessment for cats over eight years old.
Recognise the signs of hyperthyroidism — weight loss, increased appetite, restlessness — and seek veterinary advice promptly.
Discuss all treatment options with your vet to find the approach best suited to your cat.
Consider radioiodine therapy as a curative option if available and affordable.
Monitor treated hyperthyroid cats closely, especially for concurrent kidney disease after treatment.
Microchip your cat and ensure up-to-date registration to enable return if they wander due to hyperthyroid restlessness.