Cutaneous IgG4 ‐Related Disease Accompanied by Granulomatous Vasculitis: A Case Report

ABSTRACT IgG4‐related disease (IgG4‐RD) is a systemic fibroinflammatory disorder characterized by dense infiltration of IgG4‐positive plasma cells, fibrosis, and elevated serum IgG4 levels. Although various cutaneous manifestations of IgG4‐RD have been described, and vasculitic changes have occasionally been reported, granulomatous vasculitis is not considered a typical histopathological feature of cutaneous IgG4‐RD. We report a 93‐year‐old woman with a history of IgG4‐RD who presented with long‐standing subcutaneous nodules on both knees. Histopathological examination revealed dense lymphoplasmacytic infiltration with marked fibrosis, obliterative phlebitis, and granulomatous vasculitis characterized by vascular destruction with multinucleated giant cells. Immunohistochemistry demonstrated a marked increase in IgG4‐positive plasma cells with a high IgG4/IgG‐positive plasma cell ratio. Comprehensive clinical, serological, and histopathological evaluation excluded other causes of granulomatous vasculitis, including eosinophilic granulomatosis with polyangiitis, granulomatosis with polyangiitis, and sarcoid vasculitis. The lesions responded favorably to systemic corticosteroid therapy. To our knowledge, granulomatous vasculitis has not been recognized as a typical histopathological feature of cutaneous IgG4‐RD. This case suggests that granulomatous vasculitis may rarely occur in cutaneous lesions of IgG4‐RD, but additional cases are needed to confirm this association.