Prevalence of antineuronal antibodies in patients with encephalopathy of unknown etiology: Data from a nationwide registry in Korea

•Among 1699 patients with encephalopathy of unknown etiology, autoantibody was identified in 6.12%.•Autoimmune encephalopathy comprised a significant portion of idiopathic cases.•Anti-NMDA receptor antibody was the most common autoantibody in age under 40.•Anti-LGI1 antibody was the most common autoantibody in age 40 and over.

We aimed to evaluate the prevalence of antineuronal antibodies in a nationwide cohort of patients with encephalopathy of unknown etiology. We screened 1699 patients with idiopathic encephalopathy who were referred from 70 hospitals across Korea for autoimmune synaptic and classic paraneoplastic antibodies. Those with cerebellar degeneration, sensory polyneuropathy or other paraneoplastic syndromes without encephalopathy were not included in this study. One-hundred and four patients (6.12%) had antibody-associated autoimmune encephalopathy. Autoimmune synaptic antibodies were identified in 89 patients (5.24%) and classic paraneoplastic antibodies were identified in 16 patients (0.94%). The patients with antibody-associated autoimmune encephalopathy comprised a small but significant portion of the total number of patients with encephalopathy of unknown cause.

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