Hyperthyroidism is the most common hormone problem (endocrinopathy) seen in older cats in the UK and results in an overproduction of thyroid hormones. Like us, cats have two thyroid glands either side of the neck, but some can also have thyroid tissue in the chest. The thyroid gland enlargement (goitre) is usually the result of a benign adenoma (growth) in one or both glands, but can also, more rarely, be the result of a more aggressive condition.
Clinical Signs
The most common clinical signs of hyperthyroidism in cats include weight loss (despite a normal or increased appetite), increased drinking and urination, poor coat quality, hyperactivity or ‘kitten like’ behaviour, vocalising or crying at night and restlessness, diarrhoea and sometimes vomiting. There is often extra strain on the heart that can cause heart disease. Affected cats often have thickening (hypertrophy) of the heart muscle and a fast heart rate. These common heart symptoms can cause an increased blood pressure can increase the risk of blindness or a stroke.
Hyperthyroidism Diagnosis
In some cases, your vet may be able to feel an enlarged thyroid gland in your cat’s neck. If the clinical signs and history fit, we will recommend a blood test to check the levels of thyroid hormone.
Hyperthyroidism Treatment
The good news is that hyperthyroidism is a common and treatable condition. There are several treatment options for the treatment of hyperthyroidism in cats:
- Diet (specialised diet)
- Oral medications (once or twice daily liquid or tablets)
- Surgery (to remove one or both of the affected thyroid glands)
- Radioactive iodine (available specialist centres in the UK)
Radioactive iodine treatment is considered the gold standard treatment for hyperthyroidism in cats. Unlike medication or a low-iodine diet, radio-iodine is a permanent cure for feline hyperthyroidism. It’s also almost always a one-off treatment. They require specialist treatment at one of several specialist centres across the country. Whilst treatment is curative the associated costs are often prohibitive and requires the cat to stay at these centres for long periods of time due to them being radio-active.
Hyperthyroidism is a disease of older cats, and this unfortunately means that some may have concurrent disease(s), especially kidney and heart disease. Hyperthyroidism can sometimes mask concurrent problems such as kidney disease, so we will often start by stabilising their condition with oral medication for several weeks before surgical management. If your cat does have concurrent problems this may affect the treatment options, this can be discussed in more detail with your veterinarian.
Hyperthyroid Surgery (Thyroidectomy)
Surgery (thyroidectomy) involves the removal of the affected thyroid gland(s). Cats are typically stabilised on medication for several weeks before the operation to minimise risks associated with the general anaesthetic. The affected thyroid gland is removed (unilateral thyroidectomy) and the remaining side checked. The parathyroid glands are small glands very close to each of thyroid gland which controls calcium levels. Great care is taken to avoid damaging the parathyroid glands and their blood supply. Low calcium levels can be a serious complication. This risk is avoided if only one thyroid gland is removed at a time, however, it is not uncommon that the remaining thyroid gland becomes a problem later.
Post-operative monitoring of the thyroid hormone and calcium levels is required following surgery as well as regular check-ups to monitor your cats weight, heart rate and progress.