Combined immunoglobulin G kappa nephropathy: monoclonal immunoglobulin deposition disease and proximal tubulopathy: monoclonal gammopathy of renal significance or smoldering multiple myeloma? Case report and review of literature

Multiple myeloma (MM) is consistently preceded by precursor states of monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). These represent a continuum of progression of the tumor burden from the absence of symptoms or signs of end-organ damage towards full-blown symptomatic disease. MGUS, by definition presenting by monoclonal gammopathy without end organ damage, in fact might be associated with the numerous end organ lesions, first of all pathologic renal conditions. The term monoclonal gammopathy of renal significance (MGRS) was proposed by International Kidney and Monoclonal Gammopathy Research Group in order to discriminate the pathologic nature of these diseases from the truly benign MGUS. Spectrum of MGRS, caused by the deposition of monoclonal immunoglobulin’s or fragments thereof as organized and non-organized deposits, includes more commonly AL amyloidosis, monoclonal immunoglobulin deposition disease (MIDD) and light-chain proximal tubulopathy (LCPT). Same variants are seen in patients with MM and SMM. We present a rare case of combined immunoglobulin G kappa nephropathy: MIDD and proximal tubulopathy in a patient, manifested with acute kidney injury and diagnosed with SMM after 6 years of scrutinous repeated evaluation. .