Hyperthyroidism is a very common condition in older cats involving over-production of thyroid hormones by the thyroid glands. The thyroid glands are located in the neck and when enlarged can often be palpated, this is called a goitre.
Hyperthyroidism is treatable, with the majority of cases showing a resolution of clinical signs and attaining a good quality of life as long as treatment is continued.
Thyroid hormones drive metabolic rate and as a result hyperthyroidism can produce some quite dramatic symptoms.
Symptoms of hyperthyroidism
* Increased appetite
* Weight loss and loss of condition in general
* Increase thirst
* Matted coat
* Increased restlessness, irritability and other behavioural changes
* Vomiting and diarrhoea
* Panting when hot/stressed
* Rapid heart rate
* Goitre (enlarged thyroid) palpable on neck
* Advanced cases may show a loss of appetite and generalized weakness as a result of toxicity on the body from thyroid hormones
The thyroid hormone has an affect on all organs in the body and can contribute to the development of heart failure and high blood pressure. These conditions may need to be treated along side of the hyperthyroidism and should be monitored for.
Diagnosis will require a clinical examination by your veterinary surgeon and blood tests to test the level of thyroid hormone in the blood. Kidney and liver parameters will also be checked on these blood tests. The liver will often show some affect of the hyperthyroidism and this will be monitored on further blood tests. Kidney disease, whilst not overtly caused by the hyperthyroidism can be contributed to if high blood pressure has resulted, and will often occur alongside hyperthyroidism. The increase blood supply to the kidney as a result of the overactive thyroid can result in kidney disease being masked on blood tests. As treatment for the hyperthyroid condition begins, a subsequent deterioration in kidney readings may be noted on further blood tests. Sometimes this will require some careful balancing of the two conditions, depending on which is causing the most problems.
Once hyperthyroidism is diagnosed, treatment and any additional problems that will need treating alongside will be discussed by your vet. The most common form of treatment involves oral medication with either Felimazole or Vidalta. This treatment will be required life long. A starting dose will be decided upon and then adjusted based on follow up blood tests. The tablets are small in size and most cats will tolerate treatment without much fuss. The fact that the medication is administered orally also allows flexibility in treatment depending on what other conditions we encounter along the way. A hyperthyroid cat on medication should restore its body weight and a more normal appetite. Its coat and behaviour should resort back to the cat you knew previously!
Another treatment option is surgical removal of one or both thyroid glands. This is a procedure with potential complications that your vet will discuss with you, but if life long oral medication is not an option this procedure can possibly provide a cure. Unfortunately thyroid tissue can exist as ectopic tissue in addition to the two glands, this tissue is not surgically accessible and if it is present hyperthyroidism can develop again despite thyroid glands having been removed. Before any surgery oral medication will be necessary to stabilize the thyroid to reduce the risks of the anaesthetic and to check the effect of treatment on the kidneys.
The final treatment is the use of radioactive iodine which can actually cure the cat of the condition. Whilst it is a safe treatment for the cat, it is only available at specialist centres and the cat would have to remain there hospitalised for 6 weeks, until the radiation falls to acceptable levels. All these treatments options can be discussed with your vet as necessary.