Plasma Exchange as an Adjunctive Therapeutic Option for Severe and Refractory Antineutrophil Cytoplasmic Antibody-Negative Microscopic Polyangiitis and Granulomatosis with Polyangiitis

<i>Background and Objectives</i>: This study investigated and compared the efficacy of therapeutic plasma exchange (PEX) between antineutrophil cytoplasmic antibody (ANCA)-positive and ANCA-negative patients with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA) presenting with diffuse alveolar haemorrhage (DAH) and rapidly progressive glomerulonephritis (RPGN). <i>Materials and Methods</i>: A total of 336 patients with ANCA-associated vasculitis were screened, and 34 patients with MPA/GPA receiving PEX for DAH or RPGN were included. PEX was performed a total of 5-6 times consecutively (three times a week × 2 weeks) in all 34 patients. All-cause mortality (ACM) and end-stage kidney disease (ESKD) were evaluated as poor outcomes of MPA/GPA. Clinical data and poor outcomes were compared between ANCA-positive and ANCA-negative MPA/GPA patients receiving PEX. <i>Results</i>: The median age of the 34 MPA/GPA patients was 67 years (15 men and 19 women), of whom two were diagnosed with ANCA-negative vasculitis. Among the 34 patients, 28 (82.4%) received PEX owing to RPGN, and 6 (17.6%) due to DAH. During follow-up, 13 patients (38.2%) died, and 15 (44.1%) progressed to ESKD. Serum protein and C-reactive protein levels at AAV diagnosis were higher in ANCA-positive MPA/GPA patients than in ANCA-negative patients, although the difference was not statistically significant. Similarly, there were no differences in ACM or ESKD between the two groups during follow-up. Survival analysis showed that ANCA-positive MPA/GPA patients did not have significantly different cumulative patient or ESKD-free survival rates compared to ANCA-negative patients. <i>Conclusions</i>: This pilot study is the first to demonstrate the clinical feasibility of PEX in managing severe and refractory ANCA-negative MPA and GPA.