The thyroid gland is a hormonally active gland. It produces important hormones that are responsible for the body’s heat and energy balance, among other things.

Hyperthyroidism occurs mainly in cats from the age of 10 years.

In hyperthyroidism in cats, the thyroid gland produces an excessive number of hormones. The cause of this increased production is usually a tumorous (benign) enlargement of the thyroid gland.

Increased production of thyroid hormones leads to an increase in basal metabolic rate, i.e., the cat consumes more energy than it can take in through food.

The consequences include weight loss with increased or constant appetite.

However, the thyroid hormones also have an influence on other organ systems. For example, hyperactivity and restlessness may occur. Many cats show increased fluid intake and urinate more and/or more frequently. The coat may become shaggy and lacklustre. Vomiting and diarrhoea are often secondary symptoms of hyperthyroidism.

Hyperthyroidism is often accompanied by an increase in blood pressure. The consequences of this increase in blood pressure can be kidney damage or retinal detachment with subsequent loss of vision. Furthermore, the thyroid hormones can influence heart activity. The heart rate increases. The consequence is a thickening of the heart muscle and associated with this, a reduced pumping capacity of the heart (often reversible through therapy).

The diagnosis is determined by the preliminary report, palpation of the thyroid gland and a blood test.

There are three options for the treatment of hyperthyroidism:

1. Surgical removal of the affected thyroid gland
2. Radioiodine therapy (destruction of the tumorous areas of the thyroid gland by means of applied radioactive iodine, only possible in a few veterinary centres in Germany)
3. Drug treatment using thyrostatic drugs, which inhibit the excessive formation of thyroid hormones.

Treatment with thyrostatic drugs (lifelong) can be in the form of tablets or a liquid. The medication is usually well tolerated by the cats.

Under therapy, there is a normalisation of thyroid function, accompanied by a reduction in the changes described above.

Since the circulating thyroid hormones cause an increased blood flow through the kidneys, more urinary substances are excreted in hyperthyroidism. A concomitant renal insufficiency may remain undetected. Under therapy of hyperthyroidism, renal insufficiency can then be recognised (unmasked). For therapy control and monitoring of the kidney function, it is important to check the blood values three weeks after the start and then at regular, individually determinable intervals. This way, the dose can be individually adjusted, and rapid intervention is possible in the event of concomitant renal insufficiency.