Monoclonal gammopathy of renal significance: Spectrum of diseases and approach to a case.

The occurrence of kidney diseases associated with a monoclonal gammopathy in the absence of symptomatic multiple myeloma is increasingly recognized. When the kidney is involved, the monoclonal etiology of these diseases results in clinical and laboratory features distinct from those of other disease, necessitating the nomenclature monoclonal gammopathy of renal significance (MGRS). The detection of these monoclonal diseases involving the kidney is important since they are poorly responsive to conventional immunosuppression and instead require clone-directed therapy. The new International Kidney and Monoclonal research group consensus definition of MGRS includes all proliferative conditions of B cells and/or plasma cells. Renal lesions due to monoclonal immunoglobulins are quite capable of progression with resulting end-stage renal disease development. Hence, these lesions require therapeutic intervention even if they do not satisfy myeloma criteria or the presence of any myeloma defining event. The spectrum of renal lesions that can be observed in a case of MGRS is wide and mirrors the list that may be seen in a case of any plasma cell neoplasm. This includes Ig light chain, heavy chain, and heavy and light chain amyloidosis; immunotactoid glomerulonephritis (GN); monoclonal immunoglobulin deposition disease including light chain, heavy chain, or heavy and light chain disease; light chain proximal tubulopathy; crystal-storing histiocytosis; proliferative GN with monoclonal immunoglobulin deposits; C3 glomerulopathy with monoclonal gammopathy and cast nephropathy. The initial approach after histological assessment is based on presence or absence of monoclonal immunoglobulin deposits. If monoclonality is evident, it is important to distinguish between conditions with deposition of intact immunoglobulin molecule or light chains only. The treatment of MGRS is directed at the underlying neoplastic B-cell or plasma cell clones.