A 70-year-old woman with acute renal failure. Crystal-storing histiocytosis.

Crystal-storing histiocytosis (CSH) is a rare disorder characterized by accumulation of immunoglobulin light chain within histiocytes in one or more organ systems, typically in association with multiple myeloma or, less frequently, with other conditions such as lymphoplasmacytic lymphoma, the use of certain medications, or even polyclonal gammopathies. The reason why only a few patients with multiple myeloma develop CSH, while the majority do not, is unknown, but it may at least partially reflect a defect in intralysosomal degradation because simple light chain overproduction is not sufficient for the development of CSH. Interestingly, CSH is associated with improved survival in multiple myeloma patients, perhaps due to earlier detection and treatment of myeloma because of the symptoms associated with CSH.