# Progression of IgM Monoclonal Gammopathy of Renal Significance (MGRS) to Symptomatic Waldenström Macroglobulinemia: A Case Report

## TL;DR

A case shows how IgM-MGRS can progress to Waldenström macroglobulinemia, emphasizing the need for early diagnosis and treatment.

## Contribution

This case report provides new clinical insight into the progression of IgM-MGRS to a symptomatic hematologic malignancy.

## Key findings

- IgM-κ monoclonal proteinuria progressed to monoclonal immunoglobulin deposition disease and Waldenström macroglobulinemia.
- Treatment with tirabrutinib resolved both kidney and systemic symptoms rapidly.
- Early renal biopsy and intervention are critical in managing IgM-MGRS.

## Abstract

Monoclonal gammopathy of renal significance (MGRS) is characterized as renal impairment caused by monoclonal protein but does not fulfill the criteria for specific hematologic malignancies. Most MGRS cases involve IgG, IgA, or light chains, but IgM‐MGRS remains poorly understood.

We present a 74‐year‐old woman with IgM‐κ monoclonal proteinuria who initially declined further evaluation. Later, anemia was identified, and a systemic work‐up revealed monoclonal immunoglobulin deposition disease in the kidney and symptomatic Waldenström macroglobulinemia. Treatment with a Bruton's tyrosine kinase inhibitor, namely tirabrutinib, rapidly resolved both proteinuria and anemia.

This case highlights the importance of early renal biopsy and prompt intervention in suspected IgM‐MGRS.