Causes of Hyperthyroidism in Cats
The thyroid is responsible for dispersing the appropriate levels of hormones the cat needs in order to maintain healthy organ function. If a tumor on the thyroid affects the ability to function properly, and the hormones are released irregularly, it can do serious damage to organ function. If the tumors found to cause hyperthyroidism, are benign tumors, they are called adenomas. If they are malignant tumors, which are far less common, they are called adenocarcinomas. Understanding the function of a healthy thyroid, and how it takes part in the endocrine system, is key to understanding the causes of hyperthyroidism.
The thyroid is an integral piece of the endocrine puzzle, because it is in charge of converting iodine, absorbed from ingested food, into hormones. The thyroid cells are special, because they are the only cells with the ability to absorb iodine, and they combine the iodine with the amino acid thyroxine to create the hormones. These hormones are T4 and T3, thyroxine, and triodothronine respectively. These hormones are used to send messages, through the blood stream, to control the animal’s metabolism, which is the conversion of oxygen and caloric intake into energy. These messages are sent to every cell in the body in order to maintain a metabolic balance. They thyroid is controlled by the pituitary gland, which determines the existing hormone levels, and tells the thyroid to produce more or less.
Adenomas, or small benign tumors located on one or both thyroid glands, can cause the thyroid to overproduce the T4 and T3 hormones. The presence of the tumors reduces the thyroid’s ability to receive accurate information from the pituitary gland, resulting in improper dispersion of the appropriate hormone levels.
Adenocarcinomas are very rare, but can be found to cause hyperthyroidism in older cats. They are malignant tumors on the thyroid glands, which grow rapidly and can spread throughout the body. These tumors are cancerous, and prevent the thyroid cells from maintaining a hormone balance.
There are several schools of thought, when talking about the causes of these tumors, benign or malignant. Some researchers believe that an iodine deficiency can impact the development of tumors, by making the thyroid work harder. Other researchers believe that there are chemical pollutants called polybrominated biphenyl ethers (PBEs), used in anything from building materials to electronics and textiles, that may cause the tumors. Another suspected cause is the chemical bisphenol-A (BPA,) which is used in the inside lining of cat food cans. The exact root cause is still under investigation.