Anti-myeloperoxidase antibody positivity in patients without primary systemic vasculitis

Objective. We aimed to elucidate the frequency and associations of MPO-ANCA positivity in patients without ANCA-associated vasculitis (AAV), in a large urban, multi-ethnic teaching hospital. Methods. Retrospective review of 200 patients identified as MPO-ANCA positive over a five-year period at Royal Free Hospital, London, UK. Results. The incidence of anti-MPO positivity in patients without AAV was 39.5%. Gastrointestinal tract disorders, infections and other connective tissue disorders made up the majority of diagnoses, and there was a higher incidence of other concomitant autoantibodies compared to the group with known AAV. Renal disease was common in non-vasculitic patients with anti-MPO antibody positivity (occurring in 48%), the majority of whom went on to renal biopsy to exclude vasculitic involvement. Conclusion. The high incidence of MPO-ANCA positivity in patients with non-vasculitic conditions highlights the need for careful clinical correlation and confirmatory tissue diagnosis.