Clinical Outcomes of Patients with Dual Positivity for Proteinase 3 and Myeloperoxidase Specific Antineutrophil Cytoplasmic Antibodies

Objective: Granulomatous polyangiitis patients generally have ANCA targeting Proteinase 3 (PR3), while microscopic polyangiitis and eosinophilic granulomatous polyangiitis patients generally have ANCA targeting myeloperoxidase (MPO). Patients positive for both PR3-ANCA and MPO-ANCA are uncommon and any diagnostic value of this situation has not been well described. The aim of this study was to determine whether there were any patterns of clinical presentations or outcomes of patients who tested positive for both PR3-ANCA and MPO-ANCA. Methods: A retrospective clinical audit was carried out. A list of patients who had tested positive for both PR3ANCA and MPO-ANCA was obtained from ACT Pathology from 2003-2013. Medical records were then used to determine their clinical outcomes. Results: 3 of the 15 study patients were found to have ANCA-associated vasculitis (AAV), two with MPA and the other EGPA along with a non-AAV autoimmune disease. 1 patient had drug-induced vasculitis and 4 had a non-AAV autoimmune disease. An additional three patients had a non-AVV autoimmune disease, but one concurrently had a malignancy while the other two had recurrent infections. Two patients had a malignancy, another one only had recurrent infections, and the remaining patient was lost to follow up with an undiagnosed inflammatory condition. Conclusion: Pathology results showing dual positivity for PR3-ANCA and MPO-ANCA in itself does not appear to indicate any particular pattern of clinical outcome and so cannot be used to draw any clinical conclusions at the time of presentation. The 3 cases of AAV demonstrated MPO-predominance which fitted with their final diagnosis.