Lambda Light Chain Crystalline Cast Nephropathy and Proximal Tubulopathy

INTRODUCTION P lasma cell dyscrasias such as multiple myeloma (MM) result from clonal proliferation of plasma cells and subsequent overproduction of Igs, including free light chains. Renal dysfunction is a core manifestation of plasma cell dyscrasias. A broad range of kidney pathologies can occur, including light chain cast nephropathy, monoclonal Ig deposition disease, light chain amyloidosis, light chain proximal tubulopathy, and tubulointerstitial nephritis. Light chain proximal tubulopathy (LCPT) is a rare manifestation of monoclonal gammopathy and is characterized by the accumulation of monotypic light chains within the proximal tubule epithelial cells. The accumulated light chains frequently form crystals; however, noncrystalline forms of LCPT have been described. LCPT with crystals is associated with a kappa light chain in the vast majority of cases, which is discovered by either routine immunofluorescence (IF), IF, or immunohistochemistry after protease digestion of the paraffin-embedded tissue. LCPT without crystals can be seen with both kappaand lambda-restricted disease. When crystals are present, ultrastructural examination is often essential to the diagnosis as crystals may be easily missed by light microscopy. The diagnosis of LCPT is of great clinical importance. In up to 85% of patients, kidney biopsy showing LCPT is the initial clue to an underlying plasma cell dyscrasia before a diagnosis has been established or the disease has come to clinical attention. Therefore, the diagnosis of LCPT is crucial for appropriate patient management. We report an unusual case of LCPT in a 59-year-old woman associated with lambda light chain restriction with prominent intraluminal crystalline casts.