Osteolytic bone lesions in the 5T2 multiple myeloma model:: Radiographic, scanning electron microscopic, and microtomographic studies

Multiple myeloma (MM) is a B-cell malignancy characterized by a monoclonal expansion of plasma cells within the bone marrow, the presence of a monoclonal serum immunoglobulin, and the activation of osteoclastic resorption leading to osteolytic lesions. An animal model mimicking human MM consists of grafting 5T2MM cells in the C57BL/KaLwRij mouse. We have inoculated 5T2MM cells intravenously into young recipient mice. The development of the disease was monitored 9 wk later by serum electrophoresis to detect the presence of a paraprotein. Mice were killed 16 wk after inoculation of the 5T2 cells. Osteolytic lesions were analyzed by 3 different methods: numeric radiography using a Faxitron machine, SEM, and X-ray microtomography that provides 3D information and reconstruction. The first 2 methods were used to quantify bone lesions and resorption. We observed the presence of numerous small resorption cavities in the long bones on the endosteal side. The most severe lesions were localized in the metaphysis of the femur and tibia. In the 5T2MM mouse, bone surfaces undergoing resorption were significantly increased on the endosteum of the femur shaft (control: 19.2%, 5T2MM: 76.2%, p < 0.0001). This study revealed that osteolytic lesions develop both at the endosteal and trabecular level with cortical perforations occurring at the terminal stage of the disease.