Feline hyperthyroidism is an increasingly common disease characterised by overactivity of the thyroid glands. It is usually seen in middle- to old-aged cats, affecting both males and females. Affected animals have high levels of thyroid hormone in their blood, one of the major effects of which is increased metabolic rate.
Hyperthyroid cats usually show weight loss despite an increased appetite, increased activity (leading to restlessness and sometimes aggression), increased water intake, reduced coat condition and a raised heart rate.
Left untreated, hyperthyroidism can result in other complications. Having a continuously rapid heart rate and raised blood pressure can lead to heart disease as the heart struggles to cope with its increased workload. High blood pressure can also result in damage to several other organs, including the brain, eyes and kidneys.
Diagnosis of hyperthyroidism is based on the signs described above, the presence of a small, firm mass in the neck (about the size of a baked bean, though this is not always present) and, ultimately, by measuring the thyroid levels in a blood test.
There are three main treatments available for hyperthyroidism:
- Medical management: this involves the administration of anti-thyroid drugs in tablet form. It is a safe, effective and economical treatment though the condition will return when the tablets are stopped. Blood tests need to be taken at intervals to check the thyroid levels and the dose may then need to be adjusted.
- Surgical management: this is by surgical removal of the affected thyroid gland which can provide a permanent cure (unless previously unaffected thyroid tissue becomes affected later). One of the main risks with surgery is damage to the parathyroid gland, a small gland associated with the thyroid which plays a vital role in regulating calcium levels in the body. Surgical cases are usually stabilised for 3-4 weeks prior to surgery by the medical management described above.
- Radiotherapy: this is becoming increasingly popular as facilities become more easily accessible. It involves the injection of radioactive iodine, which concentrates in the overactive gland and kills it. Radiotherapy is curative in most cases with few side effects.