The role of electron microscopy for the diagnosis of glomerulopathies.

Context: Electron microscopy has been used for the morphological diagnosis of glomerular diseases for more than three decades and its value has been widely emphasized. However, recent reports have analyzed the routine use of electron microscopy critically. Its use in other areas of diagnosis such as tumor diseases has declined considerably; in addition, in view of the unavoidable financial pressure for the reduction of costs due to investigations and diagnostic routines, the selection of cases for electron microscopy has been quite rigorous.

Objective: To identify the glomerular diseases that depend on electron microscopy for a final diagnosis, by means of reviewing renal biopsies performed over a 12-year period.

Design: Prospective

Setting: Hospital Ana Costa, Hospital Guilherme Alvaro and Serviço de Anatomia Patológica de Santos, Santos, São Paulo, Brazil.

Participants: 200 consecutive renal biopsies obtained from private hospitals and the teaching hospital from 1979 to 1991 were studied.

Main Measurements: All cases were analyzed via light microscopy, immunofluorescence and electron microscopy. The diagnosis was first made via light microscopy plus immunofluorescence and then via electron microscopy.

Results: Electron microscopy was diagnostic or essential for diagnosis in 10.0% of the cases, corresponding to 3.4% of primary glomerulopathies and 100% of hereditary glomerulopathies. Electron microscopy was contributory (useful) to the diagnosis in 5.5% of the cases, confirming the preliminary diagnosis formulated on the basis of clinical and laboratory data and light microscopy plus immunofluorescence findings. We obtained a 7.5% rate of discordant immunofluorescence, which was considered as such when negative immunofluorescence findings were not confirmed by electron microscopy. The final diagnosis with the use of light microscopy plus immunofluorescence alone was 77.0%.

Conclusions: It was possible to diagnose with certainty a great percentage of glomerulopathies (82.5-90% of the cases) based on the light microscopy and immunofluorescence findings alone. Electron microscopy was essential for the diagnosis of hereditary nephropathies.