Extramedullary relapse of acute myeloid leukemia in brachial plexus after allogeneic stem cell transplantation: a case report

BACKGROUND: Allogeneic hematopoietic stem cell transplantation is a potentially curative treatment for acute myeloid leukemia. However, extramedullary relapse of acute myeloid leukemia can occur after hematopoietic stem cell transplantation, causing treatment failure. Extramedullary relapse rarely involves the peripheral nerves, and it is not influenced by the effect of the graft on leukemia. CASE PRESENTATION: We report a case of extramedullary relapse of acute myeloid leukemia in the brachial plexus of a 41-year-old woman treated with allogeneic hematopoietic stem cell transplantation (HSCT). Complete hematological remission was confirmed by bone marrow examination 1 month after HSCT, and she developed no major complications immediately after HSCT. The immunosuppressant was discontinued 5 months later. However, 2 weeks after immunosuppressant withdrawal, the patient developed left arm pain and paresthesia, with subsequent development of a mass in the left brachial plexus. She was initially diagnosed with brachial plexus neuropathy because of concomitant graft-versus-host disease. Despite the administration of immunosuppressive agents, the mass continued to enlarge. The biopsy of the lesion revealed leukemic relapse. Thus, the patient was diagnosed with extramedullary relapse and underwent radiotherapy, resulting in tumor shrinkage. CONCLUSION: Extramedullary relapse should be considered a differential diagnosis in post-transplant patients with leukemia presenting with paresthesia.