Abstract
Monoclonal gammopathy of renal significance (MGRS) is a rare heterogeneous group of kidney disorders that encompasses all disorders caused by deposition of monoclonal protein (M-protein) and its light or heavy chain fragments secreted by pre-malignant or non-malignant B-cell clones in patients who do not meet the diagnostic criteria for multiple myeloma (MM) or other B-cell malignancies. MGRS can manifest as glomerular diseases, tubulopathies, or vascular involvement with varying clinical presentations, making the diagnosis of MGRS challenging. In patients with high clinical suspicion based on preliminary blood and urine studies, the evaluation of MGRS begins with a renal biopsy followed by monoclonal studies and cytogenetic analysis. There is no standard treatment protocol for MGRS, and the current consensus suggests a clone-directed approach. If not identified and treated early, MGRS often results in poor outcomes and can lead to extrarenal manifestations, such as cardiogenic shock. Herein, we present a case involving a 43-year-old male with a rare presentation of rhabdomyolysis, rapidly progressing renal dysfunction, and cardiac dysfunction. A bone marrow biopsy did not meet the diagnostic criteria for MM or other B-cell malignancies, while a renal biopsy revealed Kappa light chain cast nephropathy, which led to the final diagnosis of MGRS.