CTVLINE B
Low-grade B cell lymphoma of mucosa-associated tissue type (MALToma)
rarely may involve the kidney. Membranoproliferative glomerulonephritis (MPGN) is an uncommon complication of B
cell lymphoma and may be related to cryoglobulin
and/or immunoglobulin synthesis by a secretory B cell
clone. We report 2 patients with the novel renal biopsy findings of coexistent MALToma and
MPGN. Both subjects presented with nephrotic proteinuria and renal insufficiency. One patient had a
serum M protein (IgG K) but neither individual had
any other clinical or serologic evidence of systemic disease, including hematolymphoid malignancy, autoimmune disease, cryoglobulinemia, or hepatitis C viral infection. Both
renal biopsies demonstrated MPGN type I with immunoglobulin deposits that in 1
case showed light chain restriction (IgM K). Electron
microscopy disclosed corresponding glomerular
electron dense deposits in subendothelial locations.
Both biopsies also contained atypical interstitial lymphoid infiltrates
comprising marginal zone (centro-cyte-like) cells
that infiltrated tubules and showed extra-capsular extension. Immunostains demonstrated a predominantly B cell population
that lacked expression of CD5 and cycline D1, and
gene rearrangement studies confirmed the presence of a monoclonal B cell
population in both cases. These findings indicate that low-grade B cell
lymphoma in the kidney may be an unexpected finding in patients with nephrotic syndrome related to MPGN. Immunophenotypic
and gene rearrangement studies are important ancillary tools for the evaluation
of atypical lymphoid infiltrates in kidney biopsies.
