| Summary: | <p>Autoimmune encephalopathies, mainly described in adults, are neurological syndromes characterized predominantly by impaired alertness usually with seizures, movement disorders, psychiatric features or autonomic instability. Well-characterised serum or cerebrospinal fluid (CSF) antibodies to neuronal surface proteins have been identified in these disorders. The aim was to define and extend the role of autoantibodies in paediatric encephalopathies. The clinical, paraclinical and immunological features of patients with autoimmune encephalopathies, acute encephalitis, N-methyl-D-aspartate receptor (NMDAR)-antibody and voltage gated potassium channel (VGKC)-complex antibodies, and in children with basal ganglia encephalitis were studied in detail.</p> <p>In 48 children with a diagnosis of probable autoimmune encephalopathy, 21 (43% ) had CNS autoantibodies, principally to NMDAR and VGKC-complexes, but children without these antibodies could also respond well to immunotherapies. Immune-mediated/autoimmune encephalitis was also the largest subgroup (34% ) of encephalitis in an Australian paediatric encephalitis cohort. NMDAR-antibodies were found in children with well-defined encephalitis, but also in patients presenting without an encephalopathy, with distinct clinico-radiological white matter syndromes, or with a neurological relapse following herpes-simplex encephalitis. Children with VGKC-complex antibodies did not have autoantibodies to the complex associated proteins leucine-rich glioma inactivated 1 (LGI1) and contactin-associated protein 2 (CASPR2) as frequently seen in adults, but were more likely to have a primary neuroinflammatory disease than in patients without these antibodies. Finally, despite a recent report, dopamine receptor antibodies or an alternative autoantibody were not found in children with basal ganglia encephalitis.</p> <p>Novel clinical syndromes were identified with NMDAR-antibodies, raising important questions about the role of NMDARs in white matter, and the relationship with preceding infections. Patients with basal ganglia encephalitis may have an alternative pathobiology mediating their disease. Moreover, antibody positivity is not essential for the diagnosis of autoimmune encephalitis and children with or without detectable neuronal antibodies may respond to immunotherapy.</p>
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