Background:Monoclonal immunoglobulin–mediated kidney disease with various patterns of damage may occur in patients with B-cell malignancies and non-malignant monoclonal gammopathies, and the latter are actually merged under the umbrella of monoclonal gammopathy of renal significance. Amyloidosis is the most well-known monoclonal immunoglobulin–related kidney damage. We focused on the rarer conditions and aimed to evaluate the non-amyloid spectrum of monoclonal immunoglobulin–mediated patterns of renal damage in real clinical practice.Methods:A single-center non-interventional retrospective study included 45 patients with pathology-proven non-amyloid monoclonal immunoglobulin–mediated kidney disease, followed during 2002–2018. Disease duration, proteinuria, serum creatinine, need for dialysis at the time of kidney biopsy, clinical diagnosis, and kidney pathology findings were analyzed.Results:No significant differences in the median age, disease duration at the time of biopsy, or main clinical presentation of kidney disease were found between patients with monoclonal gammopathy of renal significance and patients with B-cell malignancies. Pathology patterns like proliferative glomerulonephritis with monoclonal immunoglobulin deposits, membranous nephropathy, C3 glomerulopathy, cryoglobulinemic glomerulonephritis, and combinations of light chain proximal tubulopathy with monoclonal immunoglobulin deposition disease, and of C3 glomerulopathy with light chain proximal tubulopathy were found in monoclonal gammopathy of renal significance setting only. In contrast, light chain proximal tubulopathy alone, anti-glomerular basement glomerulonephritis, and combinations of cast nephropathy with light chain proximal tubulopathy, and cast nephropathy with monoclonal immunoglobulin deposition disease were associated with multiple myeloma only. Monoclonal immunoglobulin deposition disease, intracapillary monoclonal immunoglobulin M deposits, and cast nephropathy alone were seen in both settings.Conclusion:The presence of monoclonal gammopathy in patients with proteinuria and/or impaired kidney function demands kidney biopsy. Neither duration of kidney disease nor its clinical presentation allows differentiating malignant and non-malignant causes of monoclonal immunoglobulin–mediated renal damage. Several pathology patterns, even cast nephropathy, can be found both in cases of monoclonal gammopathy of renal significance and in cases of B-cell malignancies. Dual patterns of damage, including combinations of organized and non-organized deposits, or organized deposits with monoclonal immunoglobulin–induced damage without monoclonal immunoglobulin deposition, constitute up to 9%, mostly in multiple myeloma cases.
Multiple myeloma with crystal-storing histiocytosis, crystalline podocytopathy, and light chain proximal tubulopathy, revealed by retinal abnormalities
