IgG4-Related Disease Presenting as Inflammatory Midline Pseudotumor of the Face and Neck.

A 78-year-old Chinese woman presented with a one-year history of a progressively enlarging purpuric rash over the central face and nasal dorsum, with subsequent development of a firm midline neck mass. Histopathology revealed dense lymphoplasmacytic infiltrate with fibrosis and obliterative phlebitis. Immunohistochemistry showed over 200 IgG4-positive plasma cells per high-power field with an IgG4-IgG ratio exceeding 40%, and serum IgG4 was markedly elevated at 3648.0 mg/L, confirming IgG4-related disease (IgG4-RD) with a head-and-neck limited phenotype. She responded well to prednisolone. This case illustrates a rare cutaneous presentation of IgG4-RD, which should be considered in differential diagnoses of head and neck lesions.