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 monoclo nal serum immunoglobulin, and the activation of osteoclastic resorption lea ding to osteolytic lesions. An animal model mimicking human MM consists of grafting 5T2MM cells in the C57BL/KaLwRij mouse. We have inoculated 5T2MM c ells intravenously into young recipient mice. The development of the diseas e 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 radiogra phy using a Faxitron machine, SEM, and X-ray microtomography that provides 3D information and reconstruction. The first 2 methods were used to quantif y bone lesions and resorption. We observed the presence of numerous small r esorption 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 5T 2MM mouse, bone surfaces undergoing resorption were significantly increased on the endosteum of the femur shaft (control: 19.2%, 5T2MM: 76.2%, p < 0.0 001). This study revealed that osteolytic lesions develop both at the endos teal and trabecular level with cortical perforations occurring at the termi nal stage of the disease.