My Patient with Monoclonal Gammopathy of Undetermined Significance has a Kidney Problem

Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant condition signifying the presence of a B-cell lymphoproliferative disorder. By connotation, it should not meet the definition of multiple myeloma, Waldenström macroglobulinemia, or lymphoma. In addition, it cannot be responsible for any end-organ damage. Similar to polyclonal immunoglobulins (Ig), monoclonal gammopathy has been increasingly recognized as an important cause of kidney disease. The recent introduction of the term “monoclonal gammopathy of renal significance” (MGRS) highlights this importance. MGRS is similar to MGUS in which the B-cell lymphoproliferative disorder has not reached a state considered to be malignant, but differentiates itself by the presence of a monoclonal gammopathy related kidney disease. This distinction is important since it separates MGRS, which is not benign, from the MGUS condition, which is benign. It also allows for a better classification of kidney diseases caused by monoclonal gammopathies. There are many renal diseases and lesions that have been identified to be secondary to MGRS. In addition, MGRS-associated renal diseases can mimic polyclonal Ig mediated kidney diseases. Kidney biopsy with immunofluorescence is the key for diagnosing MGRS-related kidney diseases. Once the diagnosis is made, a specific evaluation is needed for the diagnosis and treatment of MGRS-related kidney diseases that differs from the polyclonal Ig counterparts.