Claudia Papi, Chiara Milano, Laura Marmolejo, Ana Beatriz Serafim, Esther Aguilar, M. Guasp, Elianet Fonseca, Mateus Mistieri Simabukuro, Raffaele Iorio, Yuki Fukami, Maria Lucia Schmitz Ferreira Santos, Takashi Miwa, Takashi Araga, Yuto Uchida, Masanori Kurihara, Satoshi Okada, Luz Victoria Garcia, Kenichi Kaida, N Cunha, Alberto Vogrig, Florian Lamblin, J. D. M. de Vries, Lívia Almeida Dutra, Romana Höftberger, Maarten J. Titulaer, Jesús Planagumà, Lídia Sabater, Eugenia Martínez‐Hernández, Thais Armangué, Francesc Graus, Takahiro Iizuka, Josep Dalmau, Marianna Spatola, Anti‐GABAAR encephalitis study group
OBJECTIVES: R) encephalitis, and assess the utility of LIM-domain-only-protein 5 (LMO5) antibodies as tumor markers. METHODS: R antibodies were confirmed by 2 techniques in serum or cerebrospinal fluid. Long-term outcomes were defined as good (modified Rankin scale, mRS = 0-1) or poor (mRS 2-5) at ≥12 months. LMO5 antibodies were assessed by cell-based assays and Western blot. RESULTS: Thirty-three patients were identified (4 children, 29 adults; median age, 5.5 and 60 years; 61% male). Ten patients (10/32, 31%) had concurrent systemic autoimmunity. Adults presented with seizures and cognitive/behavioral symptoms, often with thymoma, gastrointestinal, or other tumors (18/33, 55%), whereas children frequently had seizures and ataxia with cerebellar MRI lesions. Multifocal T2/fluid-attenuated inversion recovery hyperintensities were present at onset in 23 of 31 (74%) or developed later in those with absent or single lesions. Lesions showed dynamic changes, suggesting ongoing inflammation even without clinical correlate. Relapses occurred in 17 of 31 (55%, all adults) and were associated with older age (p = 0.02) and lack of second-line immunotherapy (p = 0.02). Four patients (4/33, 12%) died. After a 32.5-month median follow-up, 9 of 20 (45%) had persistent cognitive deficits, and 6 of 20 (30%) had a poor outcome, which was associated with relapses (p = 0.04). LMO5 antibodies were absent in patients and controls. INTERPRETATION: R encephalitis shows age-dependent presentations, most commonly seizures. MRI reveals dynamic changes consistent with an ongoing "clinically silent" inflammation. Relapses and cognitive sequelae are common and associate with not receiving second-line immunotherapy. LMO5 antibodies lack tumor-predictive value. ANN NEUROL 2026;100:139-150.