Which of the following is true about Reidel's thyroiditis

Answer- D. All the aboveA rare disorder characterized by extensive fibrosis involving the thyroid and contiguous neck structures.The presence of a hard and fixed thyroid mass clinically simulates a thyroid carcinoma.It may be associated with fibrosis in other sites in the bodn such as the retroperitoneum, and appears to be another manifestation of a systemic autoimmune IgG4-related disease, which is associated with fibrosis and tissue infiltration by plasma cells producing IgG4.