Central nervous system (CNS) myelomatosis, which is the presence of monoclonal plasma cells in the cerebrospinal fluid (CSF), is extremely rare. We report a case of CNS myelomatosis developed in a 45-year-old woman with multiple myeloma in complete response, which was achieved by allogeneic peripheral blood stem cell transplantation using a reduced-intensity conditioning regimen consisting of melphalan, fludarabine, and antithymocyte globulin. Two months after the transplant, she developed a moderate motor and sensory weakness in both lower extremities. Atypical plasma cells were found in the CSF, and immunofixation revealed monoclonal light chain in the CSF. She was given three courses of weekly intra-thecal chemotherapy consisting of methotrexate, cytarabine, and dexamethasone, which cleared the CSF. This case indicates that the allogeneic transplantation could not control CNS myelomatosis, despite successfully treating the bone marrow myeloma.

Keywords: Multiple myeloma, CNS myelomatosis, Allogeneic stem cell transplantation, Intra-thecal chemotherapy