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

Objective. 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. Methods. 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). Results. 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<0.001). MPO-GPA had significantly more frequent subglottic stenosis compared to PR3-GPA. Ear, nose, throat involvement was significantly more frequent in both GPA groups compared to MPA. Type of pulmonary involvement differed between both GPA groups and MPA with diffuse pulmonary haemorrhage being significantly more frequent in the latter (7% in PR3-GPA, 0% in MPO-GPA, 27% in MPO-MPA; p<0.001). Renal involvement was more frequent in MPO-MPA compared to both MPO-GPA and PR3-GPA (impaired renal function in 84%, 39%, and 36%, respectively; p<0.001). PR3-GPA relapsed significantly more than the other two groups. After adjusting for age, MPO-GPA was a significant risk factor for mortality [HR 4.44 (95%CI 1.46-13.52), p=0.009]. Conclusion. ANCA specificity identifies specific subsets of disease characterised by different clinical presentation and outcome within the clinical diagnosis of GPA.