title: Effect of classification on the incidence of polyarteritis nodosa and microscopic polyangiitis.
abstract: OBJECTIVE
  Polyarteritis nodosa (PAN) has been used as a generic term for systemic vasculitis. The distinction between classic PAN and microscopic polyangiitis (MPA) has not always been made. The aims of this study were to compare the American College of Rheumatology (ACR) criteria for PAN with the Chapel Hill Consensus Conference (CHCC) definitions of classic PAN and MPA, and to estimate the annual incidence of PAN and MPA.
  
  
  METHODS
  The 1990 ACR criteria and CHCC definitions for systemic vasculitis were applied to an unselected cohort of 130 patients with systemic vasculitis attending a single district hospital in the UK between February 1, 1988 and January 31, 1994.
  
  
  RESULTS
  Eight patients who met the ACR criteria for PAN and who also met the CHCC definition of MPA but not classic PAN were identified. A further 5 patients met the CHCC definition of MPA but not the ACR criteria for any other type of systemic vasculitis. No patient who met the CHCC definition of classic PAN was identified. The annual incidence of MPA was calculated to be 3.6/million (95% confidence interval 1.7-6.9), and the annual incidence of PAN (ACR criteria) was 2.4/million (95% confidence interval 0.9-5.3).
  
  
  CONCLUSIONS
  Classic PAN as defined by the CHCC is rare, because small vessel involvement is excluded from this definition.
authors.affiliation: Norfolk and Norwich Hospital, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Watts
authors.forename: V A
authors.initials: VA
authors.lastname: Jolliffe
authors.forename: D M
authors.initials: DM
authors.lastname: Carruthers
authors.forename: M
authors.initials: M
authors.lastname: Lockwood
authors.forename: D G
authors.initials: DG
authors.lastname: Scott
mesh_terms: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies / Q000097:blood; D015331:Cohort Studies; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D010488:Polyarteritis Nodosa / Q000145:classification* / Q000150:complications / Q000453:epidemiology* / Q000276:immunology; D011446:Prospective Studies
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies