An inflammatory chronic disease that causes swelling (goiter) of the thyroid gland in the neck. It occurs most often in middle-aged women and is thought to be caused by an autoimmune process, in which, for reasons that are not understood, the body begins to attack itself. The disease is known to run in families. Diagnosis usually is made on the basis of laboratory tests, but occasionally a biopsy of the goiter is done. Replacement thyroid hormone can be given to make up for the low level of hormone produced by the affected gland.