We studied the clinico-pathological differences among PR3-ANCA-positive granulomatosis with polyangiitis (PR3-GPA), MPO-ANCA-positive GPA (MPO-GPA) and microscopic polyangiitis (MPA). ANCA-associated vasculitis (AAV) was classified using the European Medicines Agency classification. We retrospectively analyzed 38 patients with GPA and 41 with MPA treated in eight hospitals in Japan. Of the patients with GPA, 17 were positive for MPO-ANCA, and 15 for PR3-ANCA. All patients with MPA were MPO-ANCA positive. The mean ages of those with MPO-GPA were 69.6 years old, 10 years older than those with PR3-GPA. The majority (82 %) of patients with MPO-GPA were woman, a significantly greater proportion than for PR3-GPA. We also found that ear, nose and throat (ENT), nervous system involvement were significantly more common in MPO-GPA, but renal function was less impaired than those with MPA. Both PR3-GPA and MPO-GPA relapsed more frequently than MPA, but overall survival was significantly better (P < 0.01 and P < 0.05, respectively). Univariate analysis identified the following factors as predictors of a poor prognosis: MPA (P < 0.01), pulmonary UIP pattern (P < 0.005) Cr ≥ 1.7 mg/dl (P < 0.01) and absence of ENT involvement (P < 0.05), which were characteristics of MPA. In our cohort, MPO-GPA was most likely to affect older women and was associated with otitis media, nervous system involvement, mild renal impairment and more favorable outcome. It is clinically useful to differentiate MPO-GPA from MPA and PR3-GPA in patients with AAV.
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