IgG4-related disease (IgG4-RD) is a rare immune-mediated inflammatory disorder that can involve salivary glands and mimic benign tumors radiologically. This report presents a case of IgG4-RD of the parotid gland initially suspected as pleomorphic adenoma. A 66-year-old female patient presented with swelling and pain in the left temporomandibular joint region. Magnetic resonance image and ultrasonography-guided fine needle aspiration suggested a benign cystic tumor, and both parotid lesions were initially suspected to be bilateral pleomorphic adenomas. Excisional biopsy was performed on the larger lesion in the left parotid gland. Histopathological examination revealed a lymphoepithelial cyst with storiform fibrosis and dense infiltration of IgG4-positive plasma cells (72/HPF). Serum IgG4 level was elevated (141 mg/dL), satisfying the diagnostic criteria for IgG4-RD. The patient was referred to rheumatology for systemic evaluation and steroid therapy was considered. This report highlights the diagnostic challenge of differentiating IgG4-RD from benign parotid tumors.
Han et al. (Sun,) studied this question.