Fibrillary glomerulopathy secondary to light chain deposition disease in a patient with monoclonal gammopathy

The pathologic manifestations of renal diseases related to monoclonal plasma cell dyscrasia include light chain deposition disease, the AL type of amyloidosis, and myeloma cast nephropathy. Light chain deposit disease (LCDD) is an uncommon condition in which monoclonal light chains are deposited in the glomeruli, tubules, and vessels causing varying degree of damage. We report a case of LCDD coincident with fibrillary glomerulonephropathy (FGN) in a 73-yr-old man with a diagnosis of monoclonal gammopathy of undetermined significance who presented with progressive renal insufficiency and mild proteinuria. The serum kappa light chain level was markedly raised. Immunofluorescent stains showed IgG along with C3 and kappa staining in glomeruli, but lambda staining was negative. Electron microscopic studies revealed diffuse punctuate-type deposits along the subendothelial areas. There were also scattered randomly oriented fibrils with a mean fibril thickness of 15-25 nm seen mainly in the glomerular mesangium, consistent with FGN. The congo red stain was negative on the histologic section. The present case illustrates that LCDD can progress to develop FGN in a patient with monoclonal gammopathy.