According to WebVet, thyroid problems in cats can stem from either too much or not enough production of the thyroid hormone. In hypothyroidism, not enough hormone is made, and the cat's metabolism decreases. In hyperthyroidism, which is particularly common in cats after middle age, too much of the hormone is being produced--often due to a thyroid gland tumor.
Symptoms of hyperthyroidism include losing weight, heightened appetite, more activity and enlargement of the thyroid gland and being felt as a lump on the neck, notes WebVet. With hypothyroidism, cats may become less energetic, and they may frequent warmer places, gain weight and experience skin problems. Causes of hypothyroidism include tumors and immune system confusion. Problems may stem from the thyroid gland itself or from the pituitary gland.
PetMD points out that adenocarcinoma, a cancer in the thyroid gland, is capable of fast growth and spreading throughout the body. It happens in cats of any age, including young cats, but is more frequent in older felines. Iodine may have something to do with thyroid function, and cats who do not get enough iodine may be more at risk for getting adenocarcinoma.
To determine thyroid problems, veterinarians run blood tests to measure thyroid hormone levels, according to WebVet. Medication can treat hyperthyroidism and hypothyroidism, although surgery to excise the thyroid gland may be necessary sometimes with hyperthyroidism.