Falde, S.

Abstract Objective ANCA-negative granulomatosis with polyangiitis (GPA) remains a diagnosis of exclusion. Clinical differences between patients with ANCA-negative vs ANCA-positive GPA have not been analysed in sizable case-control studies, and the effects of ANCA-seroconversion from negative to positive are not well documented. Methods A single-centre, sex and age matched case-control study evaluated ANCA-negative vs ANCA-positive GPA from 1 January 1996 to 31 December 2015. Patients who experienced seroconversion were the subject of a case-crossover study. Clinical data and outcomes were retrieved from electronic medical records. Results ANCA-negative GPA was identified in 110 patients; 65% were female; median age was 55 (IQR 39–65) years at time of diagnosis. Disease severity was milder in ANCA-negative GPA (BVAS/WG = 2 vs 6, P < 0.001). Mucous membranous/eye manifestations were more frequent in ANCA-negative GPA. General symptoms, pulmonary and renal involvement were more frequent in ANCA-positive GPA. Patients with ANCA-positive GPA relapsed more over 60 months (21.8% vs. 9.1%, P = 0.009) compared with ANCA-negative GPA and had shorter time to event (P = 0.043). Patients with general manifestations, BMI > 30kg/m2 and necrotizing granulomatous inflammation were more likely to relapse. The 16 patients who seroconverted into ANCA-positive during follow-up had higher mean BVAS/WG at time of diagnosis (P < 0.001) and increased incidence of relapses (P = 0.004) after seroconversion. Necrotizing granulomatous inflammation on biopsy in ANCA-negative GPA patients was identified as a risk factor for subsequent seroconversion to ANCA-positivity. Conclusion Patients with ANCA-negative GPA have milder disease and a lower frequency of relapse than those with ANCA-positive GPA. ANCA appearance portended higher disease severity and an increased frequency of relapses.