Participation of extracapillary lesions (ECL) in progression of IgA nephropathy.

To clarify long-term prognosis and risk factors of IgA nephropathy, 205 patients with the disease were followed up for a period of 1 to 22 years with a mean of 7.9 years. According to the percentage of glomeruli involved with extracapillary lesions (ECL), which were defined by crescents and fibrous adhesion of glomerular tufts to Bowman's capsule, the patients were divided into four groups: group 1-absence of ECL; group 2-less than 25%; group 3-25-50%; group 4-more than 50%. During the follow-up period, 26 patients progressed to chronic renal failure requiring hemodialysis, and one patient died of acute peritonitis. The actuarial kidney survival rate was 90.4% for 5 years and 86.0% for 10 years. Ten-year survival rates were 100% in group 1, 94.3% in group 2, 81.8% in group 3 and 25.5% in group 4. Re-biopsy specimens, observed in 31 patients after intervals of 1.4 to 13.4 years, revealed an increase of ECL in 20 patients concomitant with an apparent reduction of renal function in 13, whereas in the other 11 patients with no increase, renal function remained unchanged. These results strongly suggest that ECL plays an important role in the progression of IgA nephropathy, and renal function could be impaired by repeated formation and accumulation of these lesions.