PMC4294446_01
Bone marrow (a, b) and kidney (c-e) biopsies, light microscopy. a In situ hybridization for kappa light chain, with a positive signal indicated by blue staining (arrow). b Immunohistochemistry for plasma cells (CD138). c Lobulated glomerulus with extracapillary proliferation (crescent; star; HE). d Hypercellular glomerulus with segmental fibrinoid necrosis (arrow; HE). e Duplication of glomerular basement membrane (arrow; Jones silver).
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Bone marrow biopsy revealed an abnormal kappa positive plasma cell population (CD138-positive) representing 5% or less of the cellularity (fig. 1a, b). Ten glomeruli had cellular to fibrocellular crescents (fig. 1c), with focal fibrinoid necrosis (fig. 1d). Double contour formation of the glomerular basement membrane was frequently seen (fig. 1e).
Kidney biopsy. a-d immunofluorescence microscopy, e-h electron microscopy. a IgG staining of glomerular mesangial regions and segmental glomerular capillary walls. b Linear IgG staining of tubular basement membranes. c IgG2 subclass staining of glomerular mesangium, segmental glomerular capillary walls and the small artery wall. d Faint staining for kappa light chain in expanded mesangial regions and scant staining of glomerular and tubular basement membranes. e Mesangial electron dense deposits. f Mesangial deposits with vague linear/fibrillar substructure. g, h Glomerular capillary wall with finely granular electron dense material along the inner aspect (arrow).
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IgG (fig. 2b). IgG subclass staining demonstrated 2-3+ deposition in these locations only for IgG2 (fig. 2c), with faint staining of mesangial nodules for IgG4. Staining for light chains was negative for lambda, with trace to 1+ for kappa in expanded mesangial regions and scant staining of basement membranes (fig. 2d). The mesangial regions were moderately expanded by matrix and contained finely granular electron dense material (fig. 2e) with vague fibrils in a few segments (fig. 2f). A band of finely granular electron dense material was present along some glomerular basement membranes and in rare tubular basement membranes (fig. 2g, h).