A 75-year-old woman presented for her annual checkup with no complaints. She had a past medical history of hypertension and her blood pressure at this visit was 160/80. Laboratory findings were significant for an elevated serum creatinine at 2.1 mg/dL (baseline 1.0 mg/dL) as well as proteinuria of 855 mg/24 hr. All serologies, including proteinase-3, myeloperoxidase, and anti-nuclear antibodies were negative. A kidney biopsy was performed to evaluate the decreased kidney function and proteinuria. It revealed a total of five glomeruli were present, three of which showed a global endocapillary proliferation of large atypical cells with frequent mitotic figures (Photomicrographs A and B). These atypical cells were isolated to the glomeruli and stained positive for CD20. The remaining glomeruli did not contain any proliferative changes. Electron microscopy and immunofluorescence were both negative for immune deposits.
This is a rare subtype of extranodal diffuse large B cell lymphoma that has been known in the past by several different names and was originally thought to be a proliferation of endothelial cells; however, it is currently classified by the WHO as “intravascular large B-cell lymphoma” (IVBCL). IVLBCL most frequently affects adults over 60 and is typically widely disseminated in the small vessels of many organs at presentation. It most often presents without tumor masses or lymphadenopathy and lymphoma cells are usually not seen in peripheral blood smears. Clinical symptoms are highly variable and usually result from the occlusion of small vessels. The vast majority of cases are diagnosed in the bone marrow, liver, spleen, or skin. However, there are case reports of the diagnosis being made by kidney biopsy. In these cases, it usually manifests with slowly progressive renal failure and proteinuria which is frequently in the nephrotic range.
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