Multiple myeloma is a hematological malignancy characterized by an abnormal proliferation of monoclonal plasma cells. In some occurrences, plasma cell proliferation results in a solitary lesion (solitary bone plasmacytoma or extramedullary plasmacytoma with minimal bone marrow involvement). Approximately 50% of patients with solitary plasmacytoma develop multiple myeloma within 10 years after the initial diagnosis. While back pain and compression fractures are commonly described presentations of multiple myeloma and plasmacytoma, cauda equina syndrome related to plasma cell infiltration is rare and clinical guidelines are limited. Herein, we present a rare case of a woman with acute cauda equina syndrome (CES) secondary to solitary bone plasmacytoma and multiple myeloma.