A 62-year-old man presents with a 3-week history of brief, repetitive episodes of dystonic posturing of his left arm and face, occurring more than 50 times daily, each lasting less than 3 seconds. He remains conscious during these episodes. EEG shows the pattern marked **B** in the diagram — focal frontotemporal sharp discharges. Serum and CSF testing confirms anti-LGI1 antibodies. Which of the following is the most appropriate immediate management?
A. Thymoma screening with chest CT and surgical consultation
B. Levetiracetam monotherapy with close seizure monitoring
C. Intravenous methylprednisolone 1 g/day for 5 days plus intravenous immunoglobulin
D. Phenytoin loading followed by long-term antiepileptic drug therapy
Explanation
Why Intravenous methylprednisolone 1 g/day for 5 days plus intravenous immunoglobulin is right
Anti-LGI1 limbic encephalitis is an autoimmune disorder in which antibodies disrupt synaptic transmission at voltage-gated potassium channel complexes. Faciobrachial dystonic seizures (FBDS) — the pathognomonic brief, frequent dystonic episodes of the ipsilateral arm and face — are the clinical hallmark and represent an opportunity for early diagnosis and treatment. The focal frontotemporal sharp discharges on EEG (marked B) support this diagnosis. Antiepileptic drugs alone are typically ineffective for FBDS; immunotherapy is the definitive treatment. First-line management includes intravenous methylprednisolone 1 g/day for 5 days combined with intravenous immunoglobulin (2 g/kg over 2–5 days) to suppress the pathogenic antibody response and restore synaptic function. Early immunotherapy (within weeks of symptom onset) is associated with better cognitive outcomes and prevention of permanent hippocampal atrophy. [Lancet Neurology 2016 — Autoimmune Encephalitis Criteria]
Why each distractor is wrong
Levetiracetam monotherapy with close seizure monitoring: Antiepileptic drugs alone are ineffective for FBDS in anti-LGI1 encephalitis because the seizures arise from disrupted synaptic transmission due to antibodies, not primary neuronal excitability. Without immunotherapy, cognitive decline and hippocampal damage will progress.
Phenytoin loading followed by long-term antiepileptic drug therapy: This approach addresses seizure suppression only and ignores the underlying autoimmune pathology. Phenytoin does not target the antibody-mediated synaptic dysfunction and will not prevent the progressive memory loss and permanent neuronal damage characteristic of untreated anti-LGI1 encephalitis.
Thymoma screening with chest CT and surgical consultation: Tumor association with anti-LGI1 encephalitis is uncommon (<10%), unlike NMDAR encephalitis. Thymoma screening is not a priority in the acute management of confirmed anti-LGI1 disease and delays essential immunotherapy.
