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Discussion:

Multiple myeloma (MM) is characterized by clonal plasma cell proliferation and is defined by 10% or more bone marrow plasma cells and one or more of myeloma-defining events (hypercalcemia, renal insufficiency, anemia, and bone lesions). About 15-20% of patients with newly diagnosed multiple myeloma present with severe renal insufficiency. The most common MM-related kidney disease is light chain cast nephropathy (LCCN) resulting from co-precipitation of immunoglobulin free light chains with Tamm-Horsfall glycoproteins. Rarely, paraproteins can crystallize within proximal tubular cells (crystalline LCPT) or interstitial histiocytes (CSH). LCCN, LCPT and CSH occurring together in MM as seen in our case is extremely rare. Other unique feature of our case was λ-restricted crystalline LCPT and CSH (majority of cases reported in the literature of crystalline LCPT and CSH are κ-restricted).