Fig. 1.

Renal biopsy specimen. a Periodic acid–silver methenamine (PAM) stain [high-power field (HPF)] showing mild diffuse mesangial proliferation, diffuse thickening of glomerular basement membranes (GBMs), occasional capillary wall subepithelial spikes (arrows), and frequent internal vacuolizations (original magnification, ×400; ×1000 insert; PAM stain). b Periodic acid-Schiff (PAS) stain (HPF) showing cellular crescents and segmental necrosis, with compression or destruction of capillary loops and Bowman’s capsule (×400; PAS stain). c PAS stain (low-power field) showing that, around glomeruli with crescent formation, severe tubulointerstitial damage was accompanied by the infiltration of lymphocytes, plasma cells, neutrophils, and eosinophils, but not by vasculitis (×100; PAS stain). d Immunofluorescence staining showing diffuse, fine granular staining on capillary loops with an underlying bright linear staining of the GBMs corresponding to anti-GBM antibody (×800). e Electron microscopy revealed numerous scattered subepithelial and intramembranous deposits, some of which appear electron-lucent (black arrow), and complete overlying foot process effacement. Morphological clues in this case indicating that the membranous nephropathy (MN) is secondary rather than primary include occasional mesangial deposits and mesangial proliferation (white arrow) (×2000)