Crystal-storing histiocytosis involving the kidney in a low-grade B-cell lymphoproliferative disorder

Intracellular crystal formation in histiocytes in multiple myeloma and other lymphoproliferative disorders is an uncommon presentation. In all cases, crystal formation is associated with accumulation of histiocytes containing light chain or immunoglobulin inclusions, and the disorder has been termed crystal-storing histiocytosis. We report a case of crystal-storing histiocytosis affecting the kidney with prominent infiltration of the mesangium by large mononuclear and multinuclear cells that contained eosinophilic crystalline material in the setting of a low-grade B-cell lymphoproliferative disorder. The interstitium did not contain similar crystal-containing histiocytes. On electron microscopy, the mononuclear and multinuclear cells in the mesangium were filled with rhomboid and needle-shaped crystals. Immunofluorescence studies showed the material to be positive for λ light chains but negative for κ light chains. To our knowledge, this is the first report of crystal-storing histiocytosis involving the kidney in a low-grade B-cell lymphoproliferative disorder with an immunophenotype of a marginal zone lymphoma and of exclusive expansion of the mesangium by infiltrating histiocytes containing needle-shaped and rhomboid crystals that were positive for λ light chains. We report this case to illustrate an unusual finding of mesangial infiltration by crystal-storing histiocytes, and we review the literature of renal involvement by crystal-storing histiocytosis and crystal deposition in lymphoproliferative disorders.