Extracellular crystals in plasma cell myeloma

A 66-year-old man presented to the emergency department with weakness and back pain. Remarkable laboratory results included a hemoglobin of 6.1 g/dL (13.5–17.5 g/dL) and creatinine of 17.3 mg/dL (0.6–1.3 mg/dL). Serum protein electrophoresis showed a gamma paraprotein spike demonstrated by immunofixation to be IgG lambda. Serum free lambda light chains were markedly elevated at 11,160 mg/L (5.7–26.3 mg/L). Bone marrow biopsy demonstrated 80% plasma cells with lambda light chain restriction, confirming the diagnosis of plasma cell myeloma (Fig. 1). Strikingly, both bone marrow (panel A) and renal (panel B) biopsies showed numerous, extracellular, eosinophilic, rectangular crystals measuring as large as several cell diameters and staining positive for lambda light chains (panel C) and negative for kappa light chains (panel D). Extracellular crystals have rarely been reported in plasma cell myeloma, and to our knowledge, only once previously demonstrated in both renal and bone marrow tissue from the same patient [1]. The precise etiology of these crystals is unknown; however, they are thought to arise from the precipitation of light chains in certain cases. Our patient received plasmapheresis and hemodialysis, followed by a combination of steroids and bortezomib. Unfortunately, his disease progressed rapidly despite treatment, resulting in death from disease-related complications seven months after diagnosis.