Multiple myeloma with bone marrow extracellular crystal deposition

"Myeloma kidney" with tubular casts composed of a heterogeneous mixture of electron dense homogeneous material and Tamm-Horsfall protein, together with elongated crystals, some with a fibrillar or lattice substructure, is an important cause of myeloma-associated morbidity and mortality. 4, 15 The formation of extracellular crystalline structures within the cornea, skin, thyroid gland, intravascular space and bone marrow along with other sites has been described. 5- 9 However, this phenomenon is unusual and is limited to isolated reports. Animal experiments on mice receiving intraperitoneal injections of myeloma-associated monoclonal protein have shown tubular casts, basement membrane precipitates or crystals in mice kidneys, histology comparable to that seen in patients from whom the protein was derived. 4 Molecular analysis of the light chain sequences in patients with crystal storing histiocytosis and Fanconi's syndrome secondary to light chain gammopathy have shown unusual amino acid substitutions, altering light chain hydrophobicity. 11, 12 These data indicate that the physiochemical properties of the monoclonal protein determine its tendency to crystallise, in addition to the local concentration of the protein.