Parenchymal infiltration and lymphoma-associated membranoproliferative pattern of glomerular injury: an unusual presentation of mantle cell lymphoma.

Lymphomatous processes have been shown to involve the kidney by direct and paraneoplastic mechanisms. Direct injury can manifest by effacement of typical parenchymal architecture by the lymphomatous infiltrate, and indirect, paraneoplastic mechanisms have been associated with a variety of glomerular lesions. Mantle cell lymphoma (MCL) has rarely been reported to be associated with both direct infiltration and/or paraneoplastic glomerular lesions. We describe a patient with rapidly progressive glomerulonephritis whose renal biopsy showed effacement of the renal parenchyma by MCL and a membranoproliferative pattern of glomerular injury. The patient's bone marrow was also involved by MCL, and serology revealed small M-spikes and a positive rheumatoid factor. The clinicopathologic findings were consistent with a membranoproliferative pattern of glomerular injury secondary to MCL with infiltrative destruction of renal parenchyma. This case is unusual in that MCL was diagnosed on renal biopsy, that there was a two-pronged mechanism of renal injury, and that there were two separate monoclonal immunoglobulins elaborated by the lymphoma that could be associated with the glomerular injury. Although it is uncommon to make an initial diagnosis of lymphoma from a renal biopsy, it should be recognized that patients with lymphoma might develop clinically significant renal sequelae secondary to both direct and indirect mechanisms of lymphoma-mediated nephropathy.