Objectives: Serum IgG4 may often increases in allergic diseases. Eosinophilic granulomatosis with polyangiitis (EGPA) has an allergic phase. For this reason, it was questionable whether IgG4-RD and EGPA may share some clinical and laboratory features. In this study, we investigated whether definite IgG4-RD might share those features with EGPA. Methods: We retrospectively reviewed the medical records of 42 Korean immunosuppressive drug-naïve patients with definite IgG4-RD. The American College of Rheumatology 1990 criteria for classification (the 1990 ACR criteria) for Churg-Strauss syndrome (CSS, known as EGPA) were applied to patients who were previously diagnosed with definite IgG4-RD and had no antineutrophil cytoplasmic antibody (ANCA). Definite IgG4-RD was defined when 3 components of the comprehensive diagnostic criteria were met. Results: The median age of 42 patients was 61.0 years and 69% of them were men. The median serum IgG4 level was 379.0 mg/dL and the median IgG4+/IgG+ cells ratio was 50.0%. The most common biopsy site was the salivary gland (14.3%). Antinuclear antibody was detected in 6 patients, and test results for ANCA were negative in all patients. Among 42 patients with definite IgG4-RD without ANCA, none of them met the 1990 ACR classification criteria for EGPA. Conclusions: Definite IgG4-RD found to have no overlap with EGPA when the 1990 ACR criteria for CCS were applied to Korean patients.Key Points• None of 42 Korean patients with definite IgG4-RD without ANCA met the 1990 ACR classification criteria for EGPA.• Definite IgG4-RD found to have no overlap with EGPA in Korean patients without ANCA.
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