Epidemiology of systemic vasculitis: changing incidence or definition?

The epidemiology of the systemic vasculitides is poorly documented. Many studies have been conducted from tertiary referral centers, with resulting problems of referral bias and uncertainty of denominator population, or have involved small populations. We have estimated the incidence of the major forms of systemic vasculitis in a stable, ethnically homogeneous population of 414,000 adults from 1988 to 1994. The overall annual incidence of systemic vasculitis (excluding giant cell arteritis) is 39/million (95% confidence intervals; ranging from 31 to 47). The annual incidence of Wegener's granulomatosis is 8.5/million (range, 5.2 to 12.9), Churg-Strauss syndrome 2.4/million (0.9 to 5.3), microscopic polyangiitis 2.4/million (0.9 to 5.3), adult Henoch-Schonlein purpura 1.2/million (0.3 to 3.5), and systemic rheumatoid vasculitis 12.5/million (8.5 to 17.7). These data suggest that the overall incidence of systemic vasculitis is greater than previously thought (10/million) with Wegener's granulomatosis and systemic rheumatoid vasculitis being the most common. Whether this represents a genuine increase in incidence or increased physician awareness is uncertain.