Myeloperoxidase-ANCA-positive granulomatosis with polyangiitis is a distinct subset of ANCA-associated vasculitis: A retrospective analysis of 455 patients from a single center in China.

Objective: Antineutrophil cytoplasmic antibody (ANCA) directed to proteinase 3 (PR3) used to be considered the serologic marker for granulomatosis with polyangiitis (GPA). However, patients with myeloperoxidase (MPO)-ANCA positive GPA have been increasingly reported. The aim of this study was to analyze the clinical and pathological characteristics and outcome of Chinese patients with MPO-ANCA positive GPA.

Methods: The clinical and renal histology data, renal outcomes, response to treatment, relapse and mortality were compared between patients with MPO-ANCA positive GPA and MPO-ANCA positive microscopic polyangiitis (MPA) as well as proteinase 3 (PR3)-ANCA positive GPA.

Results: 455 patients with ANCA-associated vasculitis (AAV) were recruited in this study. 276/455 patients were classified as MPO-ANCA positive MPA, 4/455 patients were classified as PR3-ANCA positive MPA, 124/455 were MPO-ANCA positive GPA and 51/455 were PR3-ANCA positive GPA. Compared with MPO-ANCA positive MPA patients, MPO-ANCA positive GPA patients had significantly higher level of BVAS and milder renal lesion at diagnosis. The probability of developing ESRD was significantly higher in patients with MPO-ANCA positive MPA than MPO-ANCA positive GPA. MPO-ANCA positive GPA patients were likely to have relapse than MPO-ANCA positive MPA patients. Compared with PR3-ANCA positive GPA patients, MPO-ANCA positive GPA patients had significantly higher proportion of female, less constitutional symptoms and milder renal lesion at diagnosis.

Conclusions: Patients with MPO-ANCA positive GPA should be regarded as a unique subset of AAV. This subset of AAV patients had relatively milder renal injury. Although ANCA specificities play an important role in differentiating AAV, taking the disease type together to classify AAV may be more rational.