PMC7171697_01
Kidney biopsy showing glomeruli with multiple manifestations of kappa light chain injury. A: Glomerulus showing segmental endocapillary PAS-negative thrombi (arrows) and segmental endocapillary inflammation (arrowhead) (periodic acid Schiff (PAS), original magnification x 400). B: Glomerulus with segmental mesangial expansion due to silver-negative material (arrow) (periodic acid-methenamine silver, original magnification x 400). C: Immunofluorescence performed on pronase-digested formalin-fixed paraffin-embedded sections showing kappa light chain in glomerular capillary lumina and mesangial regions (original magnification x 400). D: Endocapillary accumulation of wide fibrils (arrow) and mesangial infiltration with smaller electron-dense fibrils (arrowhead) (original magnification x 10,000). E: Endocapillary crystalline fibrils averaging 112 nm with a 22 nm periodicity (original magnification x 72,000). F: Mesangial fibrils averaging 22 nm (original magnification x 29,000).
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Figure1
Light microscopy demonstrated segmental to global endocapillary hypercellularity without crescent formation. (Figure 1) One-third of the glomeruli had segmental periodic acid-Schiff (PAS)-negative, fuchsin-positive (on Masson's trichrome stain) plasma protein thrombi, and similar material was in the subendothelium and lumens of arterioles and small arteries (Figure 1). 20% of the glomeruli had segmental mesangial expansion due to silver-negative and Congo red-negative material.
A: Proteinaceous fuchsin-positive dense tubular casts (arrows), Masson's trichrome, original magnification x 400). B: Strong immunohistochemical staining for kappa light chain in a tubular cast (arrow) and in extracellular and basement membrane material (original magnification x 400). C: Tubular cast composed of fibrils and microtubules, averaging 17.7 nm (original magnification x 40,000). D: Immunofluorescence showing linear kappa light chain in all extracellular and basement membrane material (original magnification x 200). E: No lambda light chain staining by immunofluorescence (original magnification x 200). F: Powdery to finely granular electron-dense material within a tubular basement membrane (arrow) (original magnification x 19,000). G: Positive Congo red stain in interstitial amyloid (original magnification x 200). H: Immunohistochemistry for leukocyte chemotactic factor 2 (LECT2) (arrows) in interstitial Congo red-positive infiltrates (original magnification x 200).
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Figure2
There was mild tubulointerstitial scarring, and the interstitium was often mildly expanded with Congo red-positive amorphous material that exhibited apple green birefringence with polarized optics (Figure 2). Routine immunofluorescence showed linear staining of all renal basement membranes and extracellular material for kappa light chain (3+) and IgG (trace to 1+) (Figure 2).