Background: This study aimed to describe the epidemiologic characteristics of microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA) in Japan.
Methods: We used the database of the Ministry of Health, Labour and Welfare (MHLW) from 2006 to 2008, and analyzed data from 938 patients (MPA = 697, GPA = 241) who fulfilled the MHLW diagnostic criteria and had registered within a year after onset.
Results: The mean ages of the MPA and GPA patients were 69.4 ± 0.4 and 58.4 ± 1.1 years, respectively. Renal (86.9 %), chest (73.7 %), and nervous system (45.2 %) symptoms were common in MPA patients. Ear, nose, and throat (86.7 %), chest (78.0 %), and renal (60.6 %) symptoms were frequently observed in GPA patients. The concomitant use of cyclophosphamide (CY) with corticosteroids was observed in 22.2 % of the MPA patients and 58.5 % of the GPA patients. In multivariate analysis, the concomitant use of CY was associated with a younger age and pulmonary hemorrhage in MPA patients, and the avoidance of CY was associated with nervous system symptoms and rapidly progressive glomerulonephritis in GPA patients. Plasma exchanges were inducted in 5.2 % of the MPA patients and 4.1 % of the GPA patients. The addition of plasma exchange was associated with elevation of the serum creatinine level in patients with both MPA and GPA.
Conclusion: A dominance of MPA and a reduced frequency of renal involvement in GPA patients may be significant features of the Japanese population. Clinical practice relating to MPA and GPA in Japan can be characterized as follows: CY is used less commonly, and plasma exchange is employed for patients with deteriorated renal function.