Clinical and Pathological Characteristics of Non-AL Amyloidosis MGRS: A Single-Center Experience Over 10 Years.

Objective: Monoclonal gammopathy of renal significance (MGRS) is a heterogeneous and relatively recently defined disorder that encompasses many kidney and hematologic pathologies. MGRS remains a rare disease and there is a need for more literature regarding its treatment and outcomes. In this study, we share our center's experience with MGRS including incidence of different kidney pathologies, clone type, kidney and hematologic response, and progression-free survival.

Methods: Data from 35 patients diagnosed with MGRS excluding light-chain amyloidosis between 2013 and 2022 at a single Canadian tertiary care center were retrospectively analyzed. All cases required kidney biopsy. Initial treatment included regimens containing bortezomib, rituximab, or cyclosporine, or steroids only. Parameters studied included incidence of different kidney pathologies, clone type, depth of hematologic response, kidney survival (KS), overall survival (OS), and progression-free survival (PFS).

Results: Out of 35 patients, there were 10 cases of monoclonal immunoglobulin deposition disease, 8 of proliferative glomerulonephritis with immune deposits, 5 of microtubular immune deposits including immunotactoid and types 1 and 2 cryoglobulinemic nephropathy, 3 of C3 glomerulonephritis, and 9 of other diagnoses. There were 21 cases with a plasma cell clone identified in bone marrow, 2 each of B cell and low-grade lymphoma, 1 atypical T cell clone, and 9 cases without an expanded clone on bone marrow biopsy. A total of 6 patients required kidney replacement therapy and 4 patients died; the median PFS was 59.3 months. Very good partial hematologic response or better was significantly associated with decreased proteinuria but not preserved eGFR. There was a non-significant trend toward better PFS with hematologic response.

Conclusion: Our experience confirms that MGRS is a heterogeneous disease and adds to the literature concerning the diagnosis and treatment of MGRS. Successful treatment of the underlying hematologic disorder with targeted therapy is more likely to lead to an improvement in kidney function.