(B) Pathology of other MGRS lesions with nonorganized deposits and MGRS lesions without Ig deposits. (a-c): Proliferative glomerulonephritis with monoclonal immunoglobulin deposits. Glomeruli exhibit lobular accentuation due to prominent mesangial expansion by mesangial hypercellularity and sclerosis, with associated global duplication of the glomerular basement membranes and cellular interposition (a, PAS stain,  × 400). On EM, large granular subendothelial nonorganized electron dense deposits (arrow) are seen (b,  × 8000). On immunofluorescence, there is granular to semilinear global glomerular capillary wall and mesangial staining for IgG (c,  ×400) and kappa light chain, with negative staining for lambda light chain (not shown). (d-f): C3 glomerulonephritis associated with monoclonal gammopathy. The glomerulus shows global mesangial expansion by an increase in mesangial cell number and the presence of glassy silver-negative immune deposits. There is segmental duplication of the glomerular basement membranes (arrows) (d, silver stain,  × 400). On EM, large mesangial (large arrows) and small intramembranous (small arrow) electron dense deposits are evident (e,  × 8000). On immunofluorescence, there is bright global granular mesangial and glomerular basement membrane staining for C3 (f,  × 400). Glomeruli were negative for immunoglobulins and C1q (not shown). (g-i): Dense deposit disease associated with monoclonal gammopathy. The glomerulus exhibits global endocapillary hypercellularity with numerous intracapillary infiltrating neutrophils with some lymphocytes and monocytes (g,  × 400). An EM image showing highly electron dense deposits occupying most of the thickness of the glomerular basement membrane (small arrows), with nodular deposits in the mesangium (large arrow) (h,  × 6000). On immunofluorescence, there is bright global granular glomerular basement membrane and mesangial staining for C3 (i,  × 400). Glomeruli were negative for immunoglobulins and C1q (not shown). (j-k): Glomerular microangiopathy associated with monoclonal gammopathy. The glomerulus exhibits segmental mesangiolysis (arrows) and duplication of the glomerular basement membrane (j,  × 400). On EM images from a patient with POEMS syndrome shows global mesangiolysis and marked widening of the subendothelial zone by electron lucent fluffy material (k,  × 4000). POEMS, polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes.

(B) Pathology of other MGRS lesions with nonorganized deposits and MGRS lesions without Ig deposits. (a-c): Proliferative glomerulonephritis with monoclonal immunoglobulin deposits. Glomeruli exhibit lobular accentuation due to prominent mesangial expansion by mesangial hypercellularity and sclerosis, with associated global duplication of the glomerular basement membranes and cellular interposition (a, PAS stain,  × 400). On EM, large granular subendothelial nonorganized electron dense deposits (arrow) are seen (b,  × 8000). On immunofluorescence, there is granular to semilinear global glomerular capillary wall and mesangial staining for IgG (c,  ×400) and kappa light chain, with negative staining for lambda light chain (not shown). (d-f): C3 glomerulonephritis associated with monoclonal gammopathy. The glomerulus shows global mesangial expansion by an increase in mesangial cell number and the presence of glassy silver-negative immune deposits. There is segmental duplication of the glomerular basement membranes (arrows) (d, silver stain,  × 400). On EM, large mesangial (large arrows) and small intramembranous (small arrow) electron dense deposits are evident (e,  × 8000). On immunofluorescence, there is bright global granular mesangial and glomerular basement membrane staining for C3 (f,  × 400). Glomeruli were negative for immunoglobulins and C1q (not shown). (g-i): Dense deposit disease associated with monoclonal gammopathy. The glomerulus exhibits global endocapillary hypercellularity with numerous intracapillary infiltrating neutrophils with some lymphocytes and monocytes (g,  × 400). An EM image showing highly electron dense deposits occupying most of the thickness of the glomerular basement membrane (small arrows), with nodular deposits in the mesangium (large arrow) (h,  × 6000). On immunofluorescence, there is bright global granular glomerular basement membrane and mesangial staining for C3 (i,  × 400). Glomeruli were negative for immunoglobulins and C1q (not shown). (j-k): Glomerular microangiopathy associated with monoclonal gammopathy. The glomerulus exhibits segmental mesangiolysis (arrows) and duplication of the glomerular basement membrane (j,  × 400). On EM images from a patient with POEMS syndrome shows global mesangiolysis and marked widening of the subendothelial zone by electron lucent fluffy material (k,  × 4000). POEMS, polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes.

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