The distribution of electron dense deposits in the glomerulus was scrutinized by electron microscopy in 34 cases of membranoproliferative glomerulonephritis (MPGN). Seven cases underwent serial biopsies. Results are summarized as follows. (1) Mesangial deposits (MD) and subendothelial deposits (SEND) were demonstrated in nearly all biopsy specimens. Intramembranous deposits (IMD) and subepithelial deposits (SEPD), which had hitherto been considered uncommon in MPGN, were also seen in over three-fourths of the specimens. (2) According to these findings, Burkholder's Type III MPGN, characterized by the frequent presence of SEPD, seems not to be essential in the classification of MPGN. In contrast, Strife's type III MPGN, defined by the disruption of the glomerular basement membrane (GBM), appears to be appropriate for the classification, because the cases diagnosed as Strife's type III showed quite peculiar histology among the MPGN. (3) In most cases having undergone serial biopsies, cellular proliferation in the glomeruli was more improved at the second biopsy than at the first, which probably resulted from intensive medications such as the combined therapy of corticosteroids, immunosuppressants, and anticoagulants. On electron microscopy, however, electron dense deposits were not decreased, and SEPD was rather increased. Furthermore, the GBM was more thickened and showed more irregular structure in the second biopsy. (4) Humps were observed in 14 out of 41 biopsy specimens of MPGN. They were seen not only in the acute but also in the chronic stage of the disease, especially in the cases with persistent hypocomple-mentemia. These results suggest that the subepithelial deposits are more common in MPGN than considered previously, and are more closely related to the morphological changes and the progression of MPGN. In particular, humps should be a marker indicating the activity of the disease associated with hypocomplementemia, whether it is acute or chronic.
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