Objective: To report a case of gait instability and progressive asymmetrical chorea clinically confirmed as anti-IgLON5 encephalitis.

Background: Anti-IgLON5 encephalitis is a rare autoimmune neurological disorder characterized by sleep disturbances, movement disorders, bulbar dysfunction, dysautonomia, and cognitive impairment. Because of its chronic and heterogeneous clinical manifestations, it can overlap clinically with more common neurodegenerative conditions, making early diagnosis a significant challenge.

Method: We retrospectively collected clinical, laboratory, neuroimaging, and treatment data from presentation through follow-up.

Results: A 73-year-old man with a history of hypertension, dyslipidemia, type 2 diabetes, and prostate adenocarcinoma presented with a six-month history of progressive gait instability, right arm weakness. Initial MRI spine revealed cervical spondylosis with cord compression at C3-4 leading to an anterior cervical discectomy and fusion. Post-operatively, his arm strength improved, but his gait instability continued to worsen. Due to the patient’s age and persistent imbalance, a trial of levodopa was initiated. However, the patient showed no clinical improvement, and subsequently developed significant choreic movements (right > left), and cerebellar ataxia within 6 months. These movements persisted despite the discontinuation of dopaminergic therapy. Physical examination showed asymmetrical chorea (right > left), orobuccal chorea, cerebellar ataxia (right > left), and dysarthria. Cognitive function remained preserved (TMSE 27/30). There were no hallucinations, sleep problems, significant dysautonomia, or family history of neurodegenerative diseases. Brain MRI revealed no acute structural abnormalities, only non-specific white matter changes and age-related atrophy. Given the suspicion of an autoimmune etiology, cerebrospinal fluid analysis revealed normal cell counts with mildly elevated protein, and testing was positive for anti-IgLON5 antibodies.

Conclusion: This case highlights that anti-IgLON5 encephalitis can mimic common age-related movement disorders. A high index of suspicious for autoimmune etiologies should be considered when progressive gait ataxia accompanied by chorea, and bulbar symptoms. Early recognition is essential for appropriate diagnostic testing and management.

References: Grossauer A, Barket R, Krismer F, De Cleene N, Heim B, Seppi K, Hegen H, Heidbreder A. Anti-IgLON5 Disease: A Systematic Review and Meta-Analysis. Eur J Neurol. 2025 Dec;32(12):e70465.
Graus F, Sabater L, Gaig C, Gelpi E, Iranzo A, Dalmau JO, Santamaria J. Anti-IgLON5 Disease 10 Years Later: What We Know and What We Do Not Know. Neurol Neuroimmunol Neuroinflamm. 2025 Jan;12(1):e200353.
Zhang YH, Ni Y, Gao YN, Shen DD, He L, Yin D, Meng HY, Zhou QM, Hu J, Chen S. Anti-IgLON5 disease: a novel topic beyond neuroimmunology. Neural Regen Res. 2023 May;18(5):1017-1022. doi: 10.4103/1673-5374.355742. PMID: 36254983; PMCID: PMC9827781.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/anti-iglon5-encephalitis-presenting-as-chronic-progressive-asymmetrical-ataxia-and-chorea/