Cat Hyperthyroidism: Managing a Common Senior Cat Condition

Hyperthyroidism is the most common hormonal disorder in older cats and, when untreated, significantly impairs quality of life; effective treatment options are available.

Key Facts

Hyperthyroidism affects approximately 10% of cats over age 10, making it the most common feline endocrine disorder
Symptoms include weight loss despite increased appetite, hyperactivity, vomiting, and unkempt coat
Untreated hyperthyroidism causes cardiac hypertrophy, hypertension, and kidney damage over time
Radioactive iodine therapy (I-131) is curative in over 95% of cases and is considered the gold standard treatment
Daily oral medication (methimazole) is effective and less expensive but requires lifelong administration
Iodine-restricted prescription diets can control hyperthyroidism in cats that accept the diet exclusively

Welfare Considerations

Hyperthyroidism in cats causes significant welfare compromise when unrecognized or untreated. The combination of weight loss, cardiac stress, hypertension, and secondary kidney disease creates a progressive, multi-system health burden. The good news is that treatment options are excellent: radioactive iodine is curative; medication is effective and manageable; and dietary treatment suits some cats well. Early diagnosis through routine senior screening allows treatment before serious secondary damage occurs, maintaining good quality of life for months or years.

What You Can Do

Include thyroid hormone (T4) testing in annual wellness blood panels for cats over age 8
Consult your veterinarian promptly if your senior cat shows unexplained weight loss, increased appetite, or hyperactivity
Discuss treatment options including I-131, medication, and dietary management with your vet based on your cat's individual circumstances
Monitor blood pressure regularly in cats with hyperthyroidism, as hypertension requires additional management