[Significance of IgM deposition in IgA nephropathy: an appraisal based on renal re-biopsy].

Repeated renal biopsies were performed in 30 patients with primary IgA nephropathy at intervals of 6-55 months during 1983-1988. Histological and immunopathological studies were conducted for each patient and comparisons were made between the 1st and 2nd biopsy. It was found that the frequency of IgM deposition in the renal glomeruli increased significantly during the course of illness from 11/30 to 21/30, while the IgA, IgG and complement (C3, C4, C1q) deposition remained rather stationary. Comparing the group of patients who were deficient in IgM deposits with those who procured this particular Ig during the illness, there were striking differences in the frequency of occurrence of nephrosis, glomerulosclerosis, severe tubular-interstitial lesion and renal insufficiency. The frequency was much higher in the IgM deposited patients In conclusion: (1) Deposition of IgM might happen during the course of IgA nephropathy as a secondary phenomenon. (2) Presence of IgM in the glomeruli immune deposits denote a poor prognosis for patients of IgA nephropathy.