Clinical Characteristics and Outcomes of Early‐Onset Versus Late‐Onset LGI1‐Antibody Encephalitis

Background Leucine‐rich glioma‐inactivated 1 antibody (LGI1‐Ab) encephalitis predominantly affected older individuals, but has also been reported in younger patients. However, the demographic, clinical, and prognostic characteristics of early‐onset LGI1‐Ab encephalitis have yet to be systematically elucidated. This study aims to systematically describe the clinical features and outcomes of early‐onset LGI1‐Ab encephalitis and compare them with those of later‐onset cases. Methods A total of 105 patients with LGI1‐Ab encephalitis admitted to the Department of Neurology at Beijing Fengtai You'anmen Hospital were enrolled in this study between January 2019 and December 2024. All patients were divided into early‐onset (age at onset younger than 50 years) and late‐onset (age at onset 50 years or older) groups. Demographic, clinical, paraclinical, and prognostic data were compared between the two groups. Results Among the cohort, 30 (28.5%) patients had early‐onset LGI1‐Ab encephalitis, with a female predominance (17, 56.7%). Epileptic seizures, psychiatric and behavioral symptoms, and memory impairment were the most common symptoms both at disease onset and throughout the disease course. Compared to later‐onset patients, early‐onset patients exhibited a lower prevalence of faciobrachial dystonic seizures (FBDS) ( p = 0.041) and hyponatremia ( p = 0.003). Additionally, they had higher serum albumin ( p = 0.012), lower CSF protein ( p = 0.006), lower age‐normalized QAlb ( p = 0.001), and fewer epileptic waves ( p = 0.041). As for prognosis, memory deficits (11/30, 36.7%) were the most common residual symptom at follow‐up, and early‐onset patients were less likely to relapse ( p = 0.038). Conclusions This study provides the first systematic characterization of early‐onset LGI1‐Ab encephalitis. Compared to late‐onset cases, early‐onset patients showed a lower incidence of hyponatremia, milder blood–brain barrier disruption, and fewer clinical relapses.