A colloid goiter, sometimes known as a colloid nodular goiter or an endemic goiter, is a thyroid gland which has become enlarged due to a lack of iodine. Situated at the front of the neck, the thyroid gland makes thyroid hormones which regulate metabolism, affecting heart rate, temperature, digestion, energy levels and other bodily functions. Iodine is needed by the thyroid gland to manufacture thyroid hormones, and a deficiency of iodine can cause the gland to grow bigger in an attempt to increase its hormone production. Colloid goiters occur most frequently in areas where there is little iodine in the soil. This means that food grown in the soil and then eaten by the local population is likely to be deficient in iodine.
The term goiter describes any swelling of the thyroid gland, and different types of goiters can develop. A colloid goiter is an example of what is called a simple goiter. Another type of simple goiter, known as a sporadic goiter, may develop in some people. Here, the cause is usually unknown.
Thyroid problems such as the diseases hyperthyroidism and hypothyroidism may also cause goiters. In hyperthyroidism the thyroid gland is too active, while in hypothyroidism it is underactive. Both diseases are autoimmune conditions, where the body's immune system attacks the thyroid gland. Viral infections and cancers can also cause the thyroid to swell.
The symptoms of this type of goiter may not develop until the growth is large enough to put pressure on nearby structures, such as the trachea and esophagus. When the trachea, or windpipe, becomes squashed, coughing and a hoarse voice may be experienced, and, in severe cases, it may be difficult to breathe. Compression of the esophagus, the tube through which food reaches the stomach, can cause swallowing problems. The signs of a colloid goiter may be an obvious swelling in the neck, and sometimes, if the arms are lifted, the neck veins may become prominent and breathing may be limited.
While these goiters are the most common thyroid swellings worldwide, they are rare in many developed countries, where iodine is routinely added to food and table salt. It is usually necessary to carry out investigations to determine the precise cause of any thyroid enlargement. Treating colloid goiters generally involves adding extra iodine to the diet and avoiding those foods which interfere with the thyroid's use of iodine and indirectly stimulate goiter growth. The outlook for someone with a colloid goiter is usually positive once treatment is carried out.