Patients hospitalized because of small vessel vasculitides with renal involvement in the period 1975-95: organ involvement, anti-neutrophil cytoplasmic antibodies patterns, seasonal attack rates and fluctuation of annual frequencies.

OBJECTIVES

To study organ involvement, anti-neutrophil cytoplasmic antibodies (ANCA) patterns, trends in yearly frequencies and seasonal variations of symptom onset in patients hospitalized because of small vessel vasculitides during a 21 year period (1975-95).

DESIGN

A retrospective investigation was conducted of 138 patients hospitalized with a diagnosis of small vessel vasculitides, as defined by the Chapel Hill Consensus Conference, within the County of Orebro, a mixed urban and rural area of central Sweden.

SETTING

Orebro Medical Center Hospital, Orebro, Sweden and two district hospitals within the County of Orebro, Sweden.

RESULTS

During the studied period there were 19 patients with a diagnosis of Wegener's granulomatosis (WG), 70 patients with microscopic polyangiitis (MPA), 36 patients with renal limited vasculitis (RLV), two with Churge-Strauss vasculitis (C-S), seven with Henoch-Schönleins purpura (HSP) and four with essential cryoglobulinemic vasculitis (ECV). Renal involvement was present in 123 patients (89.1%). A positive c- and/or pANCA was found in nearly 90% of the 111 patients where sera were available. Calculations of frequency data, restricted to the primary catchment area for patients with ANCA associated vasculitis and renal involvement (WG, MPA, RLV) during a 21-year period (1975-95) gave a mean annual frequency of 1.6 per 100,000 adults (95% CI: 1.2-3.1); for this group of patients with the inclusion of those with C-S, HSP and ECV during the last 10 year period (1986-95) gave a mean annual frequency of 2.5 per 100,000 adults (95% CI: 1.7-3.4), for male adults 3 per 100,000 (95% CI: 1.6-4.4), and female adults 1.9 (95% CI: 0.9-2.8). A frequency peak of 6.3 per 100,000 was seen for men aged 55-64. A periodic fluctuation of the frequencies with peaks every 3-4 years was noted for patients with ANCA related vasculitis (WG, MPA, RLV) during the 21-year period 1975-95. Onset of symptoms was predominantly noticed during the winter months (December-February) for patients with a positive cANCA.

CONCLUSION

The observed frequencies in our study of patients with small vessel vasculitides were higher than those previously documented. We also showed a periodic fluctuation of the annual frequencies and a seasonal variation of symptom onset.