Pathognomonic seizures in limbic encephalitis associated with anti-LGI1 antibodies

Abstract

A 62-year-old retired supermarket worker developed a rash on her trunk after eating sausages on Good Friday, 2012. On the way to hospital, her right arm jerked involuntarily, striking her husband in the face. The rash resolved quickly with antihistamine, but over the next 13 days she had increasingly frequent stereotypical, involuntary movements of her left arm and face, lasting less than 1 s. During an event, the left side of her face would contort, her left arm would fl ex at the elbow, wrist, and metacarpophalangeal joints with fi nger extension (video), and she sometimes made brief guttural noises. She had no loss of awareness. By the time she presented to our hospital she was having these seizures up to eight times per hour. Her medical history was unremarkable and she took no regular medication. Systemic and neurological examinations, including cognition, were normal. Her serum sodium was normal. MR brain imaging showed small vessel disease, but no changes in limbic structures. Video-EEG captured multiple events associated with movement and muscle artifact, but no abnormality. The inter-ictal EEG was normal. Neuropsychological assessment showed some mild executive dysfunction, which is compatible with cerebral small vessel disease. The events were characteristic of faciobrachial dystonic seizures, and we made a clinical diagnosis of limbic encephalitis associated with antibodies to LGI1 (leucinerich glioma inactivated-1). We started treatment with intravenous methylprednisolone 1 g daily for 5 days, followed by oral tapered prednisolone for 6 weeks. There was an immediate reduction in frequency of faciobrachial dystonic seizures, and these had completely stopped by day three of treatment (appendix). 3 weeks after presentation, the result of testing for serum LGI1 antibodies returned strongly positive (319 pmol/m3; reference range <85 pmol/m3), confi rming the clinical diagnosis. The patient has remained well in the community for 18 months, with no further seizures and no cognitive sequelae. Faciobrachial dystonic seizures are a newly described seizure type that seems to be pathognomonic for limbic encephalitis associated with antibodies to the LGI1 component of the voltage-gated potassium channel complex in the brain (LGI1-antibody associated limbic encephalitis). As well as faciobrachial dystonic seizures, patients with LGI1-antibody associated limbic encephalitis may have behavioural abnormalities and cognitive and memory decline. There is frequently hyponatraemia, and MR brain imaging may show hyperintensity within the medial temporal lobe structures. All manifestations of LGI1-antibodyassociated limbic encephalitis usually respond rapidly and completely to immunotherapy, but poorly to antiepileptic drugs. Delays in diagnosis and starting treatment often mean that patients are not restored to their baseline, and may have ongoing functional limitation from their memory defi cits. Faciobrachial dystonic seizures may be the earliest manifestation of limbic encephalitis associated with LGI1-antibody, so recognition of this unique seizure type off ers an opportunity for early treatment, preventing the development of other manifestations of limbic encephalitis. Our patient was treated within 14 days of symptom onset, which is shorter than the usual interval to start of treatment. She did not develop any features of LGI1antibody associated limbic encephalitis beyond very frequent dystonic seizures, and her initial investigations were normal. We avoided the need for CSF analysis as we made the diagnosis clinically. The patient was not given anti-epileptic medications and has not needed them subsequently. In an era of increasing reliance on investigations, identifi cation of a pathognomonic clinical sign is rare. Prompt recognition of faciobrachial dystonic seizures in primary or secondary care enables treatment to be initiated while awaiting laboratory confi rmation. Faciobrachial dystonic seizures exemplify the continuing need for bedside clinical acumen.