Seasonal Influence on the Risk of Relapse at a Rise of Antineutrophil Cytoplasmic Antibodies in Vasculitis Patients with Renal Involvement

Objective. The objective of this study was to identify risk factors for a relapse at the time of an increase in antineutrophil cytoplasmic antibodies (ANCA) in patients with renal ANCA-associated vasculitis (AAV). Methods. All patients between January 2000 and November 2011 with renal AAV having an ANCA rise during remission were included. Differences in time to relapse since the ANCA rise were assessed using a Cox regression model. The level of 25-hydroxy Vitamin D (25(OH) D) was assessed at the ANCA rise and at a subsequent relapse or time-matched during remission. Results. Sixty patients had an ANCA rise, of whom 36 patients relapsed. Three risk factors were associated with a relapse at the time of the ANCA increase: previous disease activity not treated with cyclophosphamide or rituximab (HR 3.48, 95% CI 1.60-7.59), an ANCA rise during the fall season (HR 4.37, 95% CI 1.60-11.90), and an extended ANCA rise (HR 3.57, 95% CI 1.50-8.48). Levels of 25(OH) D significantly decreased during followup in relapsing patients, but not in patients who remained in remission (difference -6.3 +/- 14.4, p = 0.017 vs 2.7 +/- 16.3, p = 0.430). Conclusion. ANCA rises occurring during the fall season are more frequently followed by a relapse than ANCA rises occurring during other seasons. Although it is tempting to speculate that decreasing Vitamin D levels following the ANCA rise can be held responsible for the subsequent relapse, this remains to be determined.