Multiple lymphadenopathies in eosinophilic granulomatosis with polyangiitis: differentiating from IgG4-related lymphadenopathy.

We report a case of eosinophilic granulomatosis with polyangiitis (EGPA) in a 75-year-old man who developed mononeuritis multiplex and purpura in the lower legs concomitantly presenting with lymphadenopathies. Biopsied lymph node tissue pathologically demonstrated fibrinoid necrotizing vasculitis with perivascular eosinophil infiltration, resulting in EGPA diagnosis. Additionally, abundant IgG4-positive plasma cell infiltration exhibiting >70% IgG4/IgG ratio, without storiform pattern fibrosis and obliterative phlebitis, was observed in the biopsied lymph node. Clinical improvement was observed after corticosteroid therapy. IgG4-related lymphadenopathy (IgG4-LAD) has been defined as a distinct clinical category regardless of fulfilling IgG4-related disease classification criteria. However, some autoimmune diseases, including EGPA, can develop lymphadenopathy pathologically similar to IgG4-LAD.