Immunoglobulin G4-Related Disease Masquerading Anaplastic Thyroid Carcinoma

Immunoglobulin G4-related disease (IgG4RD) is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, as well as varying degrees of fibrosis. We report a case of a 70-year-old man with a rapid-growing cervical mass for several months. Computed tomography and positron emission tomography showed a huge, ill-defined mass involving left thyroid lobe and encasing the common carotid artery, which was clinically and radiologically suspicious for anaplastic thyroid carcinoma. Ultrasonography-guided core needle biopsy was performed and histopathology examination revealed to be consistent with IgG4RD, and the IgG4/IgG ratio was 0.6. After oral corticosteroid was administered, the mass was dramatically resolved. Because IgG4RD often presents as a single localized and infiltrated mass lesion, it can be confused and misdiagnosed as a malignancy. Thus, clinicians should consider IgG4RD as a differential diagnosis in a rapid-growing neck mass to prevent unnecessary and excessive treatments. (J Clinical Otolaryngol 2018;29:301-306)