Focal segmental glomerulosclerosis with intramembranous vesicle-like microstructures and podocytic infolding lesion

A 42-year-old woman was admitted to Kyushu University hospital because of 6 months' history of bilateral leg edema. Upon admission, ascites and pleural effusion as well as systemic edema were noted. Laboratory tests revealed hypoalbuminemia of 1.5 g/dl and massive proteinuria of 10 g/day. She was diagnosed with nephrotic syndrome. Renal biopsy revealed diffuse thickening of the glomerular basement membrane (GBM) and a crescent-like extracapillary lesion with segmental sclerosis in four of 11 glomeruli. Immunoglobulins and complements were negative by immunofluorescence examination. Therefore, we diagnosed this as focal segmental glomerulosclerosis (FSGS) rather than membranous nephropathy. Using an electron microscope, we observed a thickening of the GBM with numerous intramembranous vesicle-like microstructures and an infolding of the podocyte into the GBM. Since the microstructures were partly demarcated by a unit membrane and some of them were located very closely to the infolded podocyte, we speculated that the microstructures were derived from the podocyte. The unique electron microscopic finding of our case is a disease entity rather than a reactive phenomenon.