Eosinophilic granulomatosis with polyangiitis: etiopathogenesis, classification and clinical phenotypes

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare systemic disease that can be classified as both a hypereosinophilic condition and an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis and is characterized by granulomatous inflammation. The pathogenesis of EGPA is not completely understood. It is likely that this disease is Th2-mediated, and blood and tissue eosinophilia serves as the main diagnostic criterion. The hallmarks and main effectors of organ damage in EGPA include asthma-associated necrotizing vasculitis of small-to-medium vessels and eosinophilic proliferation. Endothelial injury and vascular inflammation in EGPA is caused by ANCA via activation of circulating neutrophils. Two clinical phenotypes of the disease have been described based on the detection of ANCA: ANCA-negative with manifestations of hypereosinophilia (for example, pulmonary infiltrates and cardiomyopathy) and ANCA-positive with clinical signs of vasculitis (for example, glomerulonephritis, purpura, and mononeuritis multiplex). Both phenotypes were confirmed by histological and genomic research. However, these two coexisting mechanisms cannot be separated in clinical practice. The aim of the article is to present current knowledge of eosinophilic and ANCA-mediated aspects of the pathogenesis, classification and clinical phenotypes of EGPA, and consider prospects for future research. Conclusion. The development of EGPA is based on eosinophilic dysfunction. This dysfunction means that patients with a genetically determined predisposition to recognize the ANCA antigen and with HLA-DQ (human leukocyte antigen DQ) alleles produce anti-myeloperoxidase autoantibodies and later develop an aberrant autoimmune process. Further comprehensive post-genomic studies are needed to identify the pathogenetic mechanisms and characterize molecular features of EGPA clinical phenotypes. The elaboration of molecular endotypes will lead to the identification of new activity biomarkers and therapeutic targets that can improve the diagnosis of EGPA and the treatment outcomes.