Neuromyelitis Optica Spectrum Disorder in a Pediatric Patient Following Haploidentical Hematopoietic Stem Cell Transplantation for Acute Myeloid Leukemia.

This report describes a rare pediatric case of seronegative neuromyelitis optica spectrum disorder (NMOSD) following a second haploidentical hematopoietic stem cell transplantation (HSCT) for relapsed acute myeloid leukemia (AML). The neurological syndrome, featuring simultaneous optic neuritis and myelitis, emerged alongside classic chronic graft-versus-host disease (GVHD) manifestations (lichenoid oral changes, arthritis) on day +145 post-transplant. The diagnosis of seronegative NMOSD was established based on clinical and MRI findings, after exclusion of infectious etiologies and absence of aquaporin-4 IgG antibodies in blood and cerebrospinal fluid. Corticosteroids were avoided due to the risk of AML relapse. Instead, plasma exchange, immunotherapy with rituximab and cyclophosphamide, followed by intravenous immunoglobulin maintenance induced rapid neurological improvement and parallel resolution of GVHD symptoms. This case underscores the central nervous system as a target for alloimmunity and presents a successful steroid-sparing treatment strategy for NMOSD manifested after allogenic HSCT.