Lymphomatous infiltration of the kidney in a patient with Waldenstrom's macroglobulinemia.

Kidney disease can be an initial presentation or a chronic manifestation of plasma cell dyscrasias. Here, we describe a rare presentation of kidney disease driven by lymphomatous infiltration of the kidney in a patient with Waldenstrom's macroglobulinemia (WM). A 70-year-old female with an 8-year history of WM (IgM, κ) was referred for declining renal function. Prior to presentation, she had stable WM disease without evidence of worsening disease burden. She had been previously hospitalized with SARS-CoV-2 infection and acute kidney injury (AKI). Her serum creatinine (sCr) peaked at 3.7 mg/dL (baseline 0.9 mg/dL) but recovered to 1.1 mg/dL by the time of discharge. Two months after discharge, her sCr increased to 1.9 mg/dL, and she had new proteinuria of 1.5 g/day. Kidney biopsy showed lymphomatous infiltration of the interstitium without glomerular involvement. Treatment with rituximab and bendamustine resulted in an improvement in renal function (sCr 1.4 mg/dL). WM is an uncommon hematologic malignancy, and extramedullary involvement, including renal involvement, is rare. This case emphasizes the importance of surveillance for kidney dysfunction in patients with plasma cell dyscrasias, even if patients appear to have stable lymphoproliferative disease.