Although extramedullary involvement in multiple myeloma (MM) emerges in various organs, muscle involvement is rarely seen and is associated with poor prognosis. It is aimed to discuss the treatment strategy in such a rare case with multiple muscle involvement in relapsed MM. Because the response to treatment is short-lived and the prognosis is poor in extramedullary involvement, effective and dynamic treatment methods for bridging should be used for clinical trials and hematopoietic stem cell transplantation.