What is hyperthyroidism in cats?
Hyperthyroidism is a hormonal disorder commonly seen in older (geriatric) cats. It occurs when the thyroid glands in the neck produce excessive thyroid hormones. This leads to symptoms such as weight loss, increased appetite, excessive drinking and urination, hyperactivity, a poor coat condition, and vomiting.
The overactivity is usually caused by benign tumours (adenomas) in one or both thyroid glands, although it typically affects only one side. Malignant tumours are rare, accounting for fewer than 3% of hyperthyroid cases.
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Treatment options
In Malaysia, anti-thyroid medication is often the first line of treatment. However, when a cat does not respond well to oral medication or becomes refractory (resistant), surgery is a viable option.
Thyroidectomy
A thyroidectomy is a surgical procedure to remove one or both thyroid glands. The goal is to remove only the abnormal tissue—the adenoma. Because hyperthyroid cats often have high blood pressure and heart disease, they are considered high-risk patients for both surgery and anaesthesia, making careful preparation essential.
Pre-operative preparation
Blood tests are performed to evaluate kidney and liver function and to assess anaesthetic risk. Whenever possible, thyroid hormone levels are first brought into the normal range with a few weeks of oral medication (usually methimazole).
If heart disease has developed as a result of hyperthyroidism, medications can help control the elevated heart rate. Blood pressure is also checked and managed before surgery.
Where available, a nuclear medicine scan is recommended to determine the extent of abnormal tissue. Unfortunately, this scanning is not currently available in Malaysia, so surgical success depends on the surgeon’s assessment. Typically, adenomas are larger than normal thyroid tissue, except when both sides are affected (seen in 10–30% of hyperthyroid cats). If both glands are significantly enlarged, surgery is generally not advised because the post-operative risks are considerable.
Post-operative care and expectations
As with any surgery, the incision site must be monitored daily for signs of infection. Anti-inflammatory medication may be prescribed to reduce swelling.
After surgery, T4 hormone levels usually take one to three months to stabilise. Cats must be monitored for hypothyroidism. Once stabilised, T4 levels should be checked twice a year.
While thyroidectomy is typically curative, normal thyroid tissue can become abnormal over time, and hyperthyroidism may recur. In some cases, hyperthyroidism can mask underlying kidney disease, which may become apparent after surgery.
Summary
Despite the risks, thyroidectomy for cats with a unilateral thyroid adenoma is often a completely curative treatment. It is a good option for cats that are difficult to medicate or that no longer respond to anti-thyroid medication.
For more information about feline thyroidectomy, please make an appointment at our Kota Damansara branch:
03-6143 5988