Anti-neutrophil cytoplasmic antibody specificity determines a different clinical subset in granulomatosis with polyangiitis

It has been suggested that anti-neutrophil cytoplasmic antibody (ANCA) specificity, rather than clinical diagnosis influences the phenotype and course of ANCA-associated vasculitis (AAV). However, preliminary evidence suggests that further combined levels of categorisation might be of clinical relevance. The aim of this study was to investigate differences in clinical presentation at disease onset and outcomes based on clinical diagnosis and ANCA specificity. Newly diagnosed patients with GPA or MPA assessed in three referral centres between 2000 and 2016 were included. Patients were grouped as MPO-ANCA-positive granulomatosis with polyangiitis (MPO-GPA), PR3-ANCA-positive-GPA (PR3-GPA), and MPO-ANCA-positive microscopic polyangiitis (MPO-MPA). Of the 143 AAV patients included (female 52%), 87 were categorised as PR3-GPA, 23 as MPO-GPA, and 33 as MPO-MPA. Patients with MPO-GPA were significantly younger than MPA patients (age 49±15 versus 63±10; p