Silver-positive kidney AL amyloidosis

Excerpt

Glomerular amyloid deposits typically involve the mesangium and are described as acellular, amorphous and negative with Jones methenamine silver stain [1]. A 71-year-old While male patient with a history of kappa light chain-only smoldering multiple myeloma underwent percutaneous kidney biopsy for nephrotic range proteinuria. Light microscopy showed diffuse and global amorphous mesangial deposits, which appeared intensely silver-positive, staining in black (Fig. 1A); segmental spicules departing from capillary loops were also visible (Fig. 1, panel A, arrow). Deposits stained positive with Congo red and showed typical apple-green birefringence under polarized light (Fig. 2A). Immunofluorescence identified kappa light chain restriction (Fig. 3). Electron microscopy confirmed the presence of mesangial randomly arranged fibrils with a diameter of 7–12 nm, positive for kappa light chain with immunogold labeling (Fig. 2B). A diagnosis of kidney limited monoclonal light chain (AL) amyloidosis was made. Silver-negativity of amorphous mesangial deposits is one of the classical morphological features of kidney AL amyloidosis [1]. Silver-positive kidney amyloid deposits have been previously described only in heavy chain or light-and-heavy chain amyloidosis, and are a relatively rare occurrence (6% of cases) [2].

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