The kidney is a target organ in plasma cell dyscrasias. Usually the offending molecules are the monoclonal light chains (LCs), but the complete immunoglobulins can participate in the pathogenesis of organ damage. The primary structure of the monoclonal proteins is at the basis of the ultrastructural organization of their aggregates which translates into characteristic kidney injuries. The kidney targeting is due to the concurrence of several factors such as the local catabolism of monoclonal LCs, specific interactions of the monoclonal proteins with tissue and cellular components, and local environmental conditions. Glomerulopathic LCs interact with mesangial cells producing, through two distinct pathways, LC amyloidosis or monoclonal immunoglobulin deposition disease. Tubulopathic LCs damage the proximal tubule causing Fanconi's syndrome or precipitate in the distal tubule determining the cast nephropathy. The use of electronmicroscopy combined with immuno-labeling has allowed the identification of other rare patterns of kidney damage. In patients with known plasma cell dyscrasia, the recognition of these patterns of renal injury should lead to appropriate therapeutic intervention.
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