Objective: To evaluate the relevance of monitoring anti-myeloperoxidase antibody (anti-MPO Ab) levels in the management of anti-MPO-associated vasculitides.
Methods: Thirty-eight patients with anti-MPO-associated vasculitides were included: microscopic polyangiitis (n=18), Wegener’s granulomatosis (n=15) and Churg-Strauss syndrome (n=5). Baseline characteristics and outcomes were recorded. Serial measurements of anti-MPO Ab levels were performed (ELISA, positive≥20 IU/mL).
Results: All patients achieved vasculitis remission after a mean time of 2.0±0.9 months, with a significant decrease in the mean anti-MPO Ab level at remission (478±598 vs. 41±100 IU/mL; P<0.001). Twenty-eight (74%) patients became anti-MPO Ab negative. After a mean follow-up of 54±38 months, 12 cases of clinical relapse occurred in 11/38 (29%) patients. Relapses were associated with an increase in anti-MPO Ab levels in 10/11 (91%) patients (34±88 vs. 199±314 IU/mL; P=0.002). The reappearance of anti-MPO Abs after achieving negative levels was significantly associated with relapse (OR 117; 95% CI 9.4-1450; P<0.001). Anti-MPO Abs showed a positive predictive value of 90% and a negative predictive value of 94% for relapse of vasculitis. Up to 60% of cases of relapse occurred less than 12 months after the reappearance of anti-MPO Abs. Relapse-free survival was significantly worse for patients who exhibited a reappearance of anti-MPO Abs than in those with persistent negative anti-MPO Abs (P<0.001). Anti-MPO Abs serum level was strongly correlated with the BVAS and the DEI (r = +0.49 ; P = 0.002).
Conclusion: Through monitoring, anti-MPO Abs are a useful marker of disease activity and a good predictor of relapse in anti-MPO-associated vasculitides.