Multiple myeloma is a plasma cell neoplasm that is characterized by involvement of the skeletal system in multiple sites. It accounts for 1% of all malignancies and is most prevalent in the 70-80 year old range. Symptoms include bone pain, anemia, fever, weight loss, and weakness, as well as neurologic symptoms.
Laboratory findings include elevated ESR, anemia, hypercalcemia and hyperuricemia. Elevated globin levels are present, usually involving IgG, but any of the immunoglobulins may be produced. The plasma cell burden will eventually displace and erode the bony trabeculae and give rise to the musculoskeletal symptoms.

Classically, multiple myeloma will appear as osteolytic lesions. These arise predominantly in the verterbral bodies, ribs, skull, pelvis and femur. However, diffuse skeletal osteopenia may be observed without focal lytic lesions. Pathologic fractures are common.

Both plain films and MDP scintigraphy have a significant false negative problem: Plain film false negative 9-25%; and, MDP false negative 40-60%. - LINK -

However, FDG PET may be useful, with a sensitivity of 85% and specificity of 92% reported. [PubMed]