Ra. Watts et al., EFFECT OF CLASSIFICATION ON THE INCIDENCE OF POLYARTERITIS-NODOSA ANDMICROSCOPIC POLYANGIITIS, Arthritis and rheumatism, 39(7), 1996, pp. 1208-1212
Objective, Polyarteritis nodosa (PAN) has been used as a generic term
for systemic vasculitis. The distinction between classic PAN and micro
scopic polyangiitis (MPA) has not always been made, The aims of this s
tudy were to compare the American College of Rheumatology (ACR) criter
ia for PAN with the Chapel Bill Consensus Conference (CHCC) definition
s of classic PAN and MPA, and to estimate the annual incidence of PAN
and MPA. Methods. The 1990 ACR criteria and CHCC definitions for syste
mic vasculitis were applied to an unselected cohort of 130 patients wi
th 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 cla
ssic 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 inci
dence of PAN (ACR criteria) was 2.4/million (95% confidence interval 0
.9-5.3). Conclusion. Classic PAN as defined by the CHCC is rare, becau
se small vessel involvement is excluded from this definition.