There are several types of thyroiditis and they sometimes can fall under different names. Hashimoto's thyroiditis is the most common. Others include De Quervain's thyroiditis, and silent thyroiditis which often appears within the first 6 months after pregnancy and childbirth. Riedel's thyroiditis is an extremely rare sclerosing disease of unknown aetiology. It is characterised by replacement of the thyroid parenchyma with dense fibrous tissue which extends beyond the thyroid capsule into surrounding structures in the neck. Acute Suppurative Thyroiditis is extremely rare and is caused by a bacterial infection in the thyroid which causes pus to collect and form an abscess within the thyroid gland. The blood test results, symptoms and treatments vary, depending on the type of thyroiditis.