Immunoglobulin G4-Related Rhinosinusitis Masquerading as Refractory Eosinophilic Chronic Rhinosinusitis: A Case Report

A 64-year-old man presented with postnasal drip, nasal obstruction, peripheral blood eosinophilia (34%), and paranasal sinus mucosal thickening, suggesting eosinophilic chronic rhinosinusitis (ECRS). However, a nasal polyp biopsy showed minimal eosinophil infiltration. A blood examination revealed polyclonal hypergammaglobulinemia and elevated serum immunoglobulin (Ig) G4 levels (5060 mg/dL). A paranasal sinus mucosa biopsy confirmed IgG4-positive plasma cell infiltration. Therefore, IgG4-related rhinosinusitis was diagnosed. Positron emission tomography showed typical organ involvement and paranasal sinus lesions, suggesting sinonasal involvement in systemic IgG4-related disease (RD). We concluded that eosinophilia may occur in IgG4-RD, and the IgG4 levels may support the diagnosis in not only refractory ECRS, but also in unexplained eosinophilia.