A 52-year-old Caucasian man presents with nephrotic syndrome (proteinuria 15 g/day, serum albumin 2.1 g/dL, edema). Renal biopsy is performed. On silver methenamine staining, the structure marked **B** (GBM spike between deposits) is visualized as black-stained projections extending outward from the basement membrane. Serum anti-PLA2R antibody is positive. Which of the following best explains the pathogenesis of this finding?
A. Immune complex deposition in the subepithelial space activating complement, with new GBM synthesis attempting to wall off the deposits
B. Podocyte necrosis leading to collapse of the capillary loop architecture
C. Direct infiltration of the GBM by activated T lymphocytes causing basement membrane destruction
Proliferation of glomerular endothelial cells in response to circulating immune complexes
D.
Explanation
Why "Immune complex deposition in the subepithelial space activating complement, with new GBM synthesis attempting to wall off the deposits" is right
The spike-and-dome appearance on silver staining is pathognomonic for membranous nephropathy. The "domes" are subepithelial immune deposits (anti-PLA2R IgG complexes in primary MN), and the "spikes" (marked B) represent new basement membrane material synthesized by the podocyte in an attempt to encircle and wall off these deposits. This is the hallmark morphologic finding that defines membranous nephropathy. The positive anti-PLA2R antibody confirms primary MN, where the target antigen is the M-type phospholipase A2 receptor on the podocyte surface. The immune complexes activate the complement cascade (C5b-9 membrane attack complex), causing podocyte injury and proteinuria. KDIGO 2021 and standard pathology texts (Robbins, Kumar & Clark) emphasize that the spike formation represents the GBM's response to subepithelial immune complex deposition.
Why each distractor is wrong
Proliferation of glomerular endothelial cells in response to circulating immune complexes: This describes proliferative glomerulonephritis (e.g., post-infectious GN, IgA nephropathy, lupus class IV), not membranous nephropathy. MN is characterized by thickening of the GBM without cellular proliferation.
Direct infiltration of the GBM by activated T lymphocytes causing basement membrane destruction: This mechanism is seen in rapidly progressive GN (RPGN) and crescentic GN, not in MN. MN does not involve crescent formation or cellular infiltration.
Podocyte necrosis leading to collapse of the capillary loop architecture: While podocyte injury does occur in MN due to complement-mediated damage, the primary morphologic feature is GBM thickening and spike formation, not capillary collapse. Capillary loop collapse is seen in collapsing glomerulopathy or advanced sclerosis.
High-YieldNEET PG
The spike-and-dome appearance on silver staining is the diagnostic hallmark of membranous nephropathy—spikes are new GBM material growing around subepithelial immune deposits; this finding alone, combined with positive anti-PLA2R, confirms primary membranous nephropathy.
