We report two cases of patients complaining of lumbar back pain of unknown etiology which were finally diagnosed as multiple myeloma. The first case was a woman in her 80s with a chief complaint of lumbar back pain. The second case was a male in his 70s. He also consulted our institution because his pain did not subside despite receiving increased doses of oral medication and nerve blocks from his previous doctor. Both patients presented with compression fractures on plain radiography, and additionally with cytopenia, hyperproteinemia, and hypoalbuminemia in blood tests. Further tests were conducted due to suspected multiple myeloma, revealing a punched-out legion in the skull and elevated levels of β2 microglobulin and Immunoglobulin G. Subsequently, both patients were transferred to the hematology department. In these two cases, we had predicted the presence of multiple myeloma from the results of initial testing and subsequently successfully provided definitive diagnoses following additional examinations.