Abstracts

Rationale: Abnormal involuntary movements are frequently seen in patients diagnosed with anti-LGI1 limbic encephalitis, previously attributed to voltage gated potassium channel antibodies (VGKC-ab) (1),2, 3). However, to date it is not clear if these abnormal movements represent seizures or an extrapyramidal movement disorder. Here we describe 3 patients with anti-LGI1 limbic encephalitis, who presented with severe movement abnormalities that were associated with ictal EEG changes.Methods: Three female patients (ages 80, 46 and 72) are described. Clinical features: All patients developed abnormal movements of face, shoulders, arms or legs (videos 1-3). These strong, massive movements were slightly slower than typical myoclonus, occurring 5 to 100 times per day. Their consciousness was preserved during the movements. EEG: Continuous video-EEG recordings showed that the longer movements were clearly associated with generalized EEG electrodecremental events (EDEs), usually preceding the onset of movement by approximately 500 milliseconds (Fig. 1), a pattern typical of epileptic tonic seizures. Imaging: Patients 1 and 2 developed hippocampal atrophy. Antibody testing: Investigations in all 3 patients confirmed high anti-LGI1 antibody titres. Response to treatment: The tonic seizures improved significantly with a combination of lamotrigine and carbamazepine in patient 1, and phenytoin and levetiracetam in patient 2. Patient 3 had a poor response to carbamazepine and levetiracetam. She had a moderate and temporary response to IVIG. Results: This is the first determination that the abnormal movements commonly seen in patients with anti-LGI1 limbic encephalitis (previously known as VGKC-ab limbic encephalitis) are tonic seizures. Though the motor movements were not typical of dyskinesias or myoclonus, in most instances ictal EEG recordings were unremarkable and, therefore, the movements could easily have been considered non-epileptic and not treated appropriately. It was only during some of the more prolonged events that an ictal EEG pattern was demonstrated, confirming that these were indeed tonic seizures. The ictal EDE pattern seen on scalp EEG, typical for tonic motor seizures, is consistent with remote onset and propagation of ictal activity. Due to the longer events captured with video-EEG an electrophysiological diagnosis was possible, and treatment with antiepileptic drugs, with or without additional immunomodulation, was instituted. Conclusions: Abnormal, involuntary movements have been described in up to 40% of patients with anti-LGI1 limbic encephalitis (1). These movements have been described as twitches (4), myoclonus (1) or stereotyped brief monomorphic movements (5). However, to date it was not known if these were seizures or a movement disorder. Our findings clearly demonstrate that these events represent tonic seizures and not an extrapyramidal movement disorder. This is important as appropriate diagnosis of these movements may allow proper treatment with antiepileptic medications (with or without the addition of immunomodulation).