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Anti-LGI1 Encephalitis — RACP Adult Medicine MCQ

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HardNeurologyAnti-LGI1 EncephalitisRACP Adult Medicine

A 42-year-old man presents with a 2-year history of recurrent episodes of confusion, seizures, and behavioural changes. Between episodes he is normal. MRI brain shows progressive temporal lobe atrophy. CSF shows lymphocytic pleocytosis and positive anti-LGI1 antibodies. What is the diagnosis?

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Correct answer: E — Neurosyphilis

Anti-LGI1 (leucine-rich glioma inactivated 1) antibodies cause autoimmune limbic encephalitis characterised by faciobrachial dystonic seizures (brief, frequent seizures involving face and arm), cognitive impairment, psychiatric symptoms, and temporal lobe pathology. Unlike anti-NMDAR encephalitis, anti-LGI1 is not commonly paraneoplastic and responds well to immunotherapy (corticosteroids, IVIg, plasma exchange; rituximab for refractory cases). It is more common in older men. Hyponatraemia (SIADH) is a characteristic associated finding.

Reference: eTG – 2025 – Neurology; Graus et al – 2016 – Autoimmune Encephalitis Criteria