Ultrastructural lesions in lightmicroscopically defined types of glomerulonephritis. A blind and semiquantitative...

Current classification of glomerulonephritis (GN) is based primarily on light microscopical (LM) histopathological criteria. The aim of the present study was to investigate the occurrence and severity of a number of electron microscopical (EM) lesions in different LM defined classes of GN in order to determine the degree of homogeneity of these classes and the degree of specificity of various EM lesions seen in GN. The analysis was performed using a blind, systematic and semiquantitative method and applied on 91 consecutive biopsies from patients with GN as well as on 11 reference biopsies. Most of the EM lesions were not restricted to a single or a few light microscopically defined classes of GN. EM lesions having direct LM counterparts used as classification criteria were generally present with high scores in the corresponding LM classes but were also present in other types of GN. When the EM-findings were compared with our original classification of the 91 biopsies it was found that about 13% of all biopsies were classified erroneously using only LM. Thus, the groups obtained with the presently used LM classification system are quite heterogenous with respect to ultrastructure and probably with respect to pathogenesis. On the other hand, it appears that many ultrastructural lesions display a more or less continuous spectrum of changes which therefore are difficult to use for classification purposes.