Autoimmune encephalitis following haematopoietic stem cell transplant: a new clinical entity or a previously unrecognised one?

Central nervous system (CNS) autoimmunity, characterized by the presence of antibodies binding to brain receptors, ion channels, and related proteins (1) is increasingly recognized in children (2). Childhood-onset autoimmune encephalitis may be associated with tumours, particularly in post-pubertal girls with N-Methyl-D-aspartate receptor (NMDAR) antibody encephalitis (3), but the majority of these encephalitides are presumed to have a post infectious trigger (1,4). Recently, in a large single-centre study of 164 Australian children presenting with encephalitis, 10% were identified as having an autoimmune aetiology, a frequency which surpassed that of any single virus identified (5), mirroring cases reported in the California encephalitis project, where the frequency of NMDAR antibody encephalitis surpassed that of any of the identified viral encephalitides (6). This discovery, that several forms of encephalitis result from neuronal antibodies, and are immunotherapy-responsive, has led to a paradigm shift in the diagnostic approach with a focus on how to recognize, diagnose and treat these conditions early (2).