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.