Quantitative electron microscopic study of membranous glomerulopathy

Primary and secondary membranous glomerulopathy (MGN) may be indistinguishable by light microscopy and immunofluorescence. It has been noted occasionally anecdotally that the distribution of subepithelial immune complex deposits by electron microscopy may differ between these two subgroups. The authors examined 23 cases of primary and 22 cases of secondary MGN and quantitated the percentage of glomerular basement membrane occupied by immune complexes for each group. Mean percentage involvement of GBM with deposits was 49% ± 15% for the primary group and 16% ± 15% for the secondary group; these were statistically significantly different at the P < 0.05 level. When far-advanced disease cases (Churg Class IV) were eliminated from the groups, the mean percentage involvement of GBM was 48% ± 15% and 12% ± 7% for the idiopathic and secondary groups, respectively (P < 0.01). The quantitative differences in involvement of the GBM with immune complex deposits between primary and secondary MGN may represent fundamentally different types of antigen-antibody complexes or variable patterns in deposition of complexes derived from the circulation or formed in situ.