IGHE and eosinophilic granulomatosis with polyangiitis: For example, a history of allergies appears in 30% and 50% of the patients with EGPA and IgG4-RD respectively.7 8 In addition, eosinophilia and elevated IgE are commonly seen in both diseases.9 10 More strikingly, the increase of IgG4 occurs in EGPA and its decrease with treatment has subsequently also been made known.11 Elevated serum IgG4 and the infiltration of IgG4 positive plasma cells in the tissue are core concepts of IgG4-RD.