Validation of new ACR/EULAR 2022 classification criteria for anti-neutrophil cytoplasmic antibody-associated vasculitis

Objective The objective of this study was to compare the American College of Rheumatology/European Alliance of Associations for Rheumatology 2022 criteria with the previous classification algorithm for anti-neutrophil cytoplasmic antibody-associated vasculitis. Methods We used data from two nationwide, prospective, inception cohort studies. The enrolled patients were classified as having eosinophilic granulomatosis with polyangiitis (EGPA), granulomatosis with polyangiitis (GPA), or microscopic polyangiitis (MPA) according to the new criteria; these criteria were compared with Watts' algorithm. Results Among 477 patients, 10.7%, 9.9%, and 75.6% were classified as having EGPA, GPA, and MPA, respectively; 6.1% were unclassifiable. Three patients met both the EGPA and MPA criteria, and eight patients met both the GPA and MPA criteria. Of 78 patients with GPA classified using Watts' algorithm, 27 (34.6%) patients were reclassified as having MPA. Ear, nose, and throat involvement was significantly less frequent in patients reclassified as having MPA than in those reclassified as having GPA. Of 73 patients unclassifiable using Watts' algorithm, 62 were reclassified as having MPA. All patients reclassified as having MPA were myeloperoxidase-anti-neutrophil cytoplasmic antibody positive, and 46 had interstitial lung disease. Conclusion Although the American College of Rheumatology/European Alliance of Associations for Rheumatology 2022 criteria cause overlapping multiple criteria fulfilments in some patients, those items contribute to classifying unclassifiable patients using Watts' algorithm into MPA.