Removal of the thyroid glands surgically is generally a cost-effective treatment option and reduces the need for long-term tablets.
Surgery has the potential to provide a life-long cure if both thyroid glands are removed. However, occasionally thyroid tissue can develop elsewhere in the neck and chest, leading to signs of hyperthyroidism to recur. If this happens medication, diet or radioactive iodine will be needed.
Anaesthetic risk in older cats is greater, and increased further by the presence of kidney disease and heart disease. Hyperthyroidism leads to a dramatically increased heart rate, which increases the risk of anaesthetic. For this reason, treatment with medication or diet is recommended for around three weeks before surgery; to bring the thyroid hormone level back down to normal and therefore reduce the anaesthetic risk, and also to ensure that underlying kidney disease is not unmasked – if it is, surgery may not be appropriate.
Thyroidectomy means removal of the thyroid gland. Unilateral thyroidectomy involves the removal of only one gland, bilateral thyroidectomy involves the removal of both. Bilateral thyroidectomy is recommended, as the disease is present in both glands in over 80% of cases. However, bilateral thyroidectomy does increase the risk of complications. The main risk is in damaging the parathyroid glands. These are small glands which control the calcium balance in the body. They sit right next to the thyroid glands in the neck and can easily be damaged or removed with the thyroid tissue. If only one side is affected, the other side should be able to cope and there should not be any problems. If both sides are damaged, the cat may show signs of low calcium:
- muscle tremors and twitching
Treatment with intravenous calcium may be required, and your cat will need calcium supplementation by liquid or tablets for a period of time. In most cases, this is only short-term while the parathyroid glands recover; however in some cases, life-long supplementation is required.
In some cases, a staged thyroidectomy is performed. This involves removing one thyroid gland initially, allowing any problems with the parathyroid glands on that side to resolve, and then removing the second thyroid gland a few weeks later. This has the benefit of reducing the risk of low calcium, however it requires two separate anaesthetics so there is an increased risk from these. Discuss with your vet the pros and cons of the different surgeries before you make your decision.