Case Report: Successful treatment of mixed-phenotype acute leukemia with cauda equina syndrome as the initial manifestation

Background Mixed-phenotype acute leukemia (MPAL) has a poor prognosis, and initial presentation with cauda equina syndrome (CES) is extremely rare. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) may be the only potentially curative modality. To our knowledge, this is the first reported case of MPAL presenting with CES at disease onset. Methods We reviewed the clinical data of a 21-year-old man with high-risk myeloid/B-lymphoid MPAL presenting with CES as the initial manifestation. The patient initially presented with lumbosacral radicular pain and lower limb numbness, which rapidly progressed to fecal and urinary incontinence and inability to ambulate. Comprehensive imaging examinations and sacral biopsy ultimately confirmed myeloid/pre-B lymphoblastic MPAL with cauda equina and lumbosacral nerve root involvement. After the patient achieved complete remission with the combination chemotherapy regimen (MTRix + VD + BCL-2i), which features high blood–nerve-barrier penetration, the patient received myeloablative conditioning based on fractionated total-body irradiation and then underwent matched unrelated donor allo-HSCT. Third-party umbilical cord blood stem cells (UCBs) and mesenchymal stem cells (MSCs) were administered as adjunctive support. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine A, mycophenolate mofetil, and short-course methotrexate. Results Neutrophil and platelet engraftment occurred on days +12 and +10 post-transplant, respectively. At the 24-month follow-up, the patient remained in minimal residual disease (MRD)-negative remission of the primary disease, free of acute and chronic GVHD, with motor strength recovery from grade 0 to grade 3. Conclusion In conclusion, evidence-based multi-agent chemotherapy followed by allo-HSCT with third-party UCBs and MSC support resulted in favorable engraftment kinetics, adequate GVHD prophylaxis, and long-term remission. These outcomes support its clinical application. These findings highlight the promising efficacy and safety of this combined treatment approach in this high-risk MPAL case.