Background: Idiopathic membranous nephropathy (IMN) is a representative form of refractory nephrotic syndrome in Japan. Although IMN is thought to run a more benign course in Japanese than in the Caucasian population, risk factors and appropriate treatment are controversial issues.
Methods: The research group supported by a grant for "Progressive Renal Disease" from the Ministry of Health, Labor and Welfare, Japan, carried out a national survey of patients with IMN and nephrotic syndrome. Of 1066 nephrotic patients with histopathologically proven IMN registered from 1975 to 1993 in 85 institutions, 949 patients were studied.
Results: The overall renal survival rates were 95.8%, 90.3%, 81.1%, and 60.5% at 5, 10, 15, and 20 years after diagnosis, respectively. When clinical and histopathologic features at onset of nephrotic syndrome were evaluated by multivariate analysis, male gender, old age (> or =60 years), high serum creatinine concentration (> or =1.5 mg/dL), and the development of tubulointerstitial lesions (> or =20% of the biopsy sample area) were significant predictors of progression to end-stage renal disease (ESRD). The renal survival rate in patients on steroid therapy was significantly higher than in patients on supportive therapy alone. Patients achieving a remission showed a significant reduction of risk for progression.
Conclusion: IMN is a disease with a comparatively good prognosis in Japan even when it is associated with nephrotic syndrome. Steroid therapy, which has not been recommended for IMN in most review articles, seems to be useful at least for Japanese patients. In particular, a remission from heavy proteinuria likely results in a favorable outcome.