Validated classification criteria for microscopic polyangiitis published for research settings

The 2022  issue of the journal Arthritis & Rheumatology publishes the American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for microscopic polyangiitis (MPA), which have been validated for clinical research use.

The validated criteria are given below:

  • Antineutrophil cytoplasmic antibody (ANCA) or anti–myeloperoxidase-ANCA positivity (+6), pauci-immune glomerulonephritis (+3), lung fibrosis or interstitial lung disease (+3), sino-nasal symptoms or signs (-3), cytoplasmic ANCA or anti–proteinase 3 ANCA positivity (-1), and eosinophil count ≥1 x 109/liter (-4).
  • After excluding mimics of vasculitis, a patient with a diagnosis of small- or medium-vessel vasculitis could be classified as having MPA with a cumulative score of ≥5 points.
  • When these criteria were tested in the validation data set, the sensitivity was 91% (95% confidence interval [95% CI] 85–95%) and the specificity was 94% (95% CI 92–96%).

The study comprising of 149 MPA patients and 408 comparators were carried out through 5 phases:

  • Identification of candidate items via consensus methodology
  • Prospective collection of candidate items at the time of diagnosis
  • Data-driven reduction of the number of candidate items
  • Review of cases to define the reference diagnosis by an expert panel
  • Derivation of a points-based risk score for disease classification

The current classification criteria help in distinguishing cases of MPA from vasculitis mimics in research settings. However, they are not appropriate for establishing vasculitis diagnosis. Other key features of the present criteria are excellent sensitivity and specificity, and incorporation of ANCA testing and modern imaging techniques.

References: Suppiah R, Robson JC, Grayson PC, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology Classification Criteria for Microscopic Polyangiitis [published online ahead of print, 2022 Feb 2]. Arthritis Rheumatol. 2022;10.1002/art.41983.