Fibrillary glomerulonephritis mimicking membranous nephropathy--a diagnostic pitfall.

Kidney biopsies in 2 females with nephrotic syndrome were suggestive of membranous nephropathy at routine light microscopy and immunohistochemistry. Electron microscopy on re-embedded paraffin tissue, however, revealed that the light microscopic pattern was due to a fibrillary glomerulonephritis with a dominant membranous manifestation. These findings suggest that (a) fibrillary glomerulonephritis may be mis-/under-diagnosed at light microscopy; and (b) in reality, a subset of therapy refractory membranous nephropathies might represent fibrillary glomerulopathies. Therefore, electron microscopy is mandatory in any case of membranous nephropathy with therapy refractory nephrotic syndrome or an unusual immunohistological staining pattern, e.g. with mesangial immunoreactivity.