Bone involvement in generalized crystal-storing histiocytosis

The abnormal secretion of monoclonal immunoglobulins observed with monoclonal gammopathies and other clonal B cell dyscrasias can be responsible for a spectrum of deposition disorders. Crystal-storing histiocytosis (CSH) is a rare disease affecting patients with B cell dyscrasias and monoclonal gammopathies, characterized by the accumulation of histiocytes that have phagocytosed an abnormal crystalline immunoglobulin. We describe 2 cases of this rare disorder with multiorgan involvement and prominent bone involvement. Magnetic resonance imaging showed bone marrow infiltration and images of avascular necrosis. Bone specimen analysis gave histological proof of diffuse bone infiltration by the abnormal histiocytes. Bone involvement, which appears to be a specific feature of CSH, links this entity to other storage disorders, such as Gaucher disease. Because the accumulation of abnormal immunoglobulin-loaded histiocytes is clearly pivotal, CSH should be considered not only as an immunoglobulin deposition disease but also as a storage histiocytic disorder.