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To the Editor:

We read with interest the recent report by Turesson et al on the incidence of extraarticular manifestations of rheumatoid arthritis (RA) in Olmsted County, Minnesota (1). In contrast to our study in Norfolk, UK, which showed a decline in the incidence of systemic rheumatoid vasculitis over 15 years (2), those authors did not observe such a decline. There are several possible explanations for the different study results. The decrease in incidence of systemic rheumatoid vasculitis in our study only occurred after the mid-1990s (Figure 1), whereas their report does not include any data from after 1994. There were differences in case identification between the 2 studies because our study was hospital based whereas Turesson et al based their study in the community. However, it is likely that patients with severe extraarticular disease will present for hospital-based care at some stage as Turesson and colleagues acknowledge in their conclusion. Our study was based on the date of onset of vasculitis and not on presentation to the hospital or diagnosis of RA. Our methods were also likely to result in identification of a higher incidence of vasculitis compared with their study because we included all patients, regardless of the date of diagnosis or duration of followup. It is worth noting that over a 15-year period, we have not observed a change in the incidence of primary systemic vasculitis (Figure 1). This suggests that the decrease of systemic rheumatoid vasculitis observed in our study is a genuine reduction (3).

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Figure 1. Incidence (cases per million population) of systemic rheumatoid vasculitis (♦) and primary systemic vasculitis (▪). Each data point corresponds to the average incidence over a 3-year period, centered at the midpoint of the 3-year period.

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Richard A. Watts DM*, Suzanne E. Lane MD*, David G. I. Scott MD†, * Ipswich Hospital, Suffolk, UK, † Norfolk and Norwich University Hospital, Norfolk, UK.