# Unusual Cases of Monoclonal Gammopathy of Renal Significance

## TL;DR

This paper presents three rare cases of kidney disease linked to abnormal immunoglobulin production, emphasizing the importance of early diagnosis and biopsy for effective treatment.

## Contribution

The paper highlights unusual MGRS cases with diverse renal and hematological features, underscoring the need for prompt biopsy and targeted therapy.

## Key findings

- A patient with monoclonal membranoproliferative glomerulonephritis and chronic lymphocytic leukemia showed stable IgG/lambda paraprotein levels.
- A case of renal thrombotic microangiopathy was linked to IgM MGUS with monotypic intracapillary pseudothrombi.
- Immunotactoid glomerulonephritis was associated with a lymphoma transformation from small B-cell lymphoma to DLBCL.

## Abstract

Monoclonal gammopathy of renal significance (MGRS) is a rare entity describing patients with renal impairment related to the secretion of immunoglobulins without hematological criteria for treatment of a specific disease. We present 3 cases of MGRS identified at our center that were either rare or difficult to diagnose. Case Presentations. The first patient presented with monoclonal membranoproliferative glomerulonephritis in the context of known chronic lymphocytic leukemia (CLL), diagnosed about 10 years prior. She presented with nephritic syndrome with serum protein electrophoresis revealing an IgG/lambda peak of less than 1 g/L, stable from the last few years. A renal biopsy confirmed a diagnosis of monoclonal membranoproliferative glomerulonephritis with granular IgG and C3 deposits of various sizes. The second patient presented with renal TMA in the context of IgM MGUS. The patient was admitted for acute nephritic syndrome and thrombotic microangiopathy. Serum protein electrophoresis demonstrated IgM/kappa paraprotein at 1.8 g/L, with a kappa/lambda ratio of 5.48. Renal biopsy demonstrated endocapillary proliferative glomerulonephritis associated with the presence of numerous monotypic IgM/kappa intracapillary pseudothrombi. Characteristic changes of thrombotic microangiopathy were also described. The third patient presented with immunotactoid glomerulonephritis likely from small B-cell lymphoma that later transformed to DLBCL. The patient presented with acute renal failure with IgM/kappa paraprotein of less than 1 g/L on electrophoresis and with a kappa/lambda ratio of 7.09. A diagnosis of immunotactoid glomerulonephritis was made on renal biopsy. Bone marrow with limited specimen revealed a B-cell infiltrate. Biopsy of a breast lesion was compatible with diffuse large B-cell lymphoma (DLBCL). Lymphomatous cells expressed IgM/kappa, thus confirming paraprotein-associated renal lesion.

We described 3 different cases of MGRS, highlighting the diversity of renal pathohistological presentations and different associated lymphoproliferative disorders. Biopsy should rapidly be considered, as early diagnosis of MGRS is essential to initiate clone-directed therapy promptly to prevent progression to ESRD or hematologic progression to malignancy.