106. HISTOLOGY FOR CLASSIFICATION OF EOSINOPHILIC GRANULOMATOSIS WITH POLYANGIITIS

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Background: Classification of eosinophilic granulomatosis with polyangiitis (EGPA) is based on clinical, laboratory and histologic characteristics. The additive value of biopsies is of great interest. Objectives: We aimed to revisit classification criteria (MIRRA and ACR criteria) in consideration of specific histopathologic features from organ biopsies. Methods: Retrospective, single-center cohort study. Inclusion criteria were asthma and tissue and/or blood eosinophilia (>1.0 × 109/L or > 10% of leucocytes). Clinical characteristics of disease, ANCA-status, distribution of histologic features and their association with disease activity were analyzed. Results: 94 patients were included (mean age with vasculitis, defined by histologic criteria, surrogate of vasculitis (mononeuritis multiplex, purpura) and/or ANCA with at least one systemic manifestation other than ENT or respiratory. MIRRA criteria were fulfilled in 65 (69.1%) patients. After proof of vasculitis 45 (83.3%) fulfilled ACR criteria. 141 biopsies from 83 patients (7 kidney, 20 ENT, 42 lung, 15 skin, 14 endomyocard, 14 GI, 4 muscle, 4 nerv, 21 bone marrow) were analyzed. Vasculitis was seen 17, tissue eosinophilia in 63 and granuloma in 9 patients. Vasculitis and granuloma were most frequent in skin biopsies (5/15 and 3/15) and tissue eosinophilia in bone marrow (19/21) and ENT biopsies (18/20). Endomyocardial biopsies were most often unspecific (9/14). Vasculitis was associated with active disease (BVAS 18.4 versus 13.3; p = 0.02) but not tissue eosinophilia (15.2 versus 11.8; p = 0.98). Diagnosis of EGPA by MIRRA criteria was based on histology in 14 (21.5%) and by ACR criteria in 18 (40%) of 45 patients. 4 (7.4%) of 54 patients would not fulfill the vasculitis criteria without histology. ACR criteria were based on histology in 18 (40%) of 45 patients. Conclusion: Histologic proof of vasculitis and tissue eosinophilia contribute to diagnosis of small vessel vasculitis and classification of EGPA. Vasculitis is most frequently seen in skin biopsies and tissue eosinophilia in ENT and bone marrow biopsies. Classification to EGPA according ACR criteria depends on histology in 40% of all patients. Disclosures: None

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