This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroiditis, Subject name: Pathology
IgG4-related disease is a newly recognized entity. Which of the following thyroid abnormality is associated with this condition? 
Select and explain. 
A. De quervain thyroiditis, B. Postpaum thyroiditis, C. Reidel thyroiditis, D. Hashimoto thyroiditis
C: Reidel thyroiditis
Answer: C: Reidel thyroiditis 
Explanation: - Riedel thyroiditis, a rare disorder associated with IgG4 characterized by extensive fibrosis involving thyroid & contiguous neck structures. - The presence of a hard & fixed thyroid mass clinically simulates a thyroid carcinoma; but unlike thyroid carcinoma it is seen in young pts. - It may be associated with fibrosis in other sites like trachea, esophagus etc resulting in stridor, dysphagia etc. - Treated by rituximab/ tomoxifen/ steroids. EXTRA EDGE: - IgG4-Related diseases are: Mikulicz syndrome (enlargement and fibrosis of salivary & lacrimal glands) Riedel thyroiditis idiopathic retroperitoneal fibrosis autoimmune pancreatitis, and inflammatory pseudotumors of orbit, lungs & kidneys.