Thyroid gland inflammation. Light micrograph of a section through thyroid gland tissue in a case of Riedel's thyroiditis. Thyroiditis, inflammation of the thyroid, has several different forms. Here, fibrosis, the formation of scar tissue, dominates the image. Riedel's thyroiditis is a rare disease that usually only affects part of the gland, which turns very hard. This can obstruct nearby organs, particularly the trachea (windpipe). Surgery may be required, but usually corticosteroid drugs are used to reduce the inflammation. It is thought to be an autoimmune disorder. The thyroid's function, secreting the metabolic hormone thyroxine, is not normally affected in Riedel's thyroiditis.