In brief
Hyperthyroidism is common in older cats. Typical signs include weight loss despite a good appetite, restlessness, increased thirst, vomiting and a rapid heart rate, although not every cat follows the textbook.
What causes it?
One or both thyroid glands produce too much thyroid hormone, usually because of benign nodular change. Thyroid hormone increases metabolic activity throughout the body and can affect the heart, blood pressure, kidneys and gastrointestinal tract.
Possible signs
- Weight and muscle loss despite normal or increased appetite.
- Restlessness, vocalisation or altered sleep.
- Increased thirst and urination.
- Vomiting, diarrhoea or an unkempt coat.
- A fast heart rate, heart murmur or high blood pressure.
- Some cats are quiet and eat poorly rather than appearing hyperactive.
Diagnosis and kidney function
Total T4 confirms many cases. Early or complicated cases may need repeat testing or additional thyroid tests. Kidney disease can be partly masked by hyperthyroidism, so renal values, urine and blood pressure should be assessed before and after treatment.
Treatment options
Options include radioactive iodine, antithyroid medication, surgery and an iodine-restricted prescription diet. Radioactive iodine can be curative in suitable cats. The best choice depends on health, access, household circumstances and whether a reversible trial is useful.
Conclusion
Hyperthyroidism is treatable, but follow-up is essential to balance thyroid control with kidney function, blood pressure and overall wellbeing.