IgG4-related skin disease, a mimic of angiolymphoid hyperplasia with eosinophilia.

Mikulicz's disease is considered one of the IgG4-related diseases that are characterized by elevated serum IgG4 concentrations and the immunohistochemical finding of IgG4-positive plasma cells. The IgG4-related diseases often exhibit a wide variety of eosinophil infiltration. A 66-year-old male with Mikulicz's disease developed multiple, nonpruritic, red papules on the left opisthotic region 2 years after diagnosis. A biopsy of the skin lesions revealed follicle-like formation in the dermis and subcutaneous tissue containing nodular lymphocytic infiltration with numerous eosinophils and plasma cells, predominately around venules, mimicking angiolymphoid hyperplasia with eosinophilia (ALHE). Immunohistochemically, most IgG-expressing plasma cells were positive for IgG4 (IgG4/IgG ratio = 72%). Our patient appeared to have a condition associated with the IgG4-related diseases. Caution should be exercised in diagnosing skin lesions of the IgG4-related diseases, which are confusingly similar in appearance and histology to ALHE.