Differential Diagnosis (1): ANCA Associated Vasculitis

Abstract

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides comprise important elements in the differential diagnosis of IgG4-related disease (IgG4-RD). ANCA-associated vasculitis (AAV) is classified into four different diseases on the basis of the clinical and pathological features and the presence/absence of extra-renal involvement. These four diseases are eosinophilic granulomatosis with polyangiitis (EGPA), granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and renal-limited vasculitis (RLV). Among these AAVs, the features of EGPA overlap substantially with those of IgG4-RD. In particular, features of bronchial asthma, tissue infiltration by eosinophils, elevated serum IgG4 levels, and tissue infiltrating IgG4-positive plasma cells are often found in both EGPA and IgG4-RD. GPA sometimes shows imaging findings very similar to those of IgG4-RD, tissue-infiltrating IgG4-positive plasma cells have also been described in abundance. Certain histopathological features, including necrotizing vasculitis, neutrophil infiltration, and granuloma, are highly atypical findings in IgG4-related tubulointerstitial nephritis and suggest AAV. AAV should be considered in cases of suspected IgG4-RD that demonstrate a suboptimal response to glucocorticoids, since many patients with GPA, MPA, EGPA, and RLV require a medication in addition to glucocorticoids in order to exert control.