Anti-neutrophil cytoplasmic antibodies and disease activity during long-term follow-up of 70 patients with systemic vasculitis.

Anti-neutrophil cytoplasmic antibodies (ANCA) have been identified as a diagnostic marker in primary systemic vasculitis, and immunofluorescence assays identify two patterns of binding: cytoplasmic (C-ANCA and perinuclear (P-ANCA). We have examined retrospectively the use of such assays in long-term monitoring of disease activity, in order to determine the relationship between presence of ANCA and relapse, and to assess their suitability as a guide to therapy. Seventy patients were studied over a period of 50 months, using clinical and laboratory criteria for the diagnosis of relapse and the internationally standardised immunofluorescence assay for detection of ANCA. In 19 patients C- or P-ANCA were detectable throughout the study period; six of these (with C-ANCA) relapsed. In 18 patients ANCA were undetectable during long-term follow-up; none of these patients relapsed. In 33 patients C- or P-ANCA were intermittently present; nine of these relapsed and all had C-ANCA detectable at the time of relapse. In six of the nine cases, relapse was accompanied or closely preceded by reappearance of C-ANCA. We conclude that continuing presence and reappearance of ANCA may identify patients who are at risk of relapse and who are most likely to benefit from long-term immunosuppressive therapy.