Hyperthyroidism in cats
Cats have two thyroid glands in their neck, one on each side.
Hyperthyroidism occurs when abnormal thyroid tissue produces an excess of thyroid hormone. The cause in 98% of cats is a benign tumour (adenoma) of the thyroid gland. In the remaining 2% of cases a malignant tumour (carcinoma) is the cause.
Treatment options for feline hyperthyroidism can include:
- Oral treatment with tablets
- Transdermal gel treatment
- Surgical removal of affected glands
- Radiation treatment with radioactive iodine
There are advantages and disadvantages with each treatment and no single method will suit every cat. Treatment needs to be individualised, taking into account several factors including age, severity of disease, general health, presence of other disease, demeanour, facilities available, cost and potential complications.
Medical therapy
Medical management involves giving tablets two or three times daily, or application of a transdermal gel to the skin (usually the inner ear), for life. This controls the release of hormone from the gland and as such the disease is controlled rather than cured. It does not require any special skills or facilities, is easy to implement but is moderately expensive in the long-term. Costs include ongoing medication, regular health checks and blood tests. Hospitalisation and anaesthesia are unnecessary and postoperative complications are avoided. Daily medication is required, which is unsuitable for some patients, and adverse reactions can occasionally occur. These include vomiting, rashes and occasionally changes in blood cell counts. Medical management is often necessary to stabilise the patient’s condition prior to surgical intervention.
Surgical therapy
Surgical treatment is relatively simple and often curative. Disadvantages include the need for an anaesthetic, recurrence in some cases, the inability to treat ectopic thyroid tissue (e.g. in the chest) and poor success rates for malignant tumours (carcinoma). Postoperative complications can include voice change, Horner’s syndrome (a nerve deficit to the eye), hypothyroidism and hypocalcaemia. The most serious is hypocalcaemia, which can cause muscle tremors/twitches and seizures. Using a “staged” surgical procedure can minimise the chance of hypocalcaemia occurring.
