A bout of confusion: Atypical presentations of Anti-Leucine-rich-Glioma-Inactivated 1(LGI-1) encephalitis – an emerging cause of limbic encephalitis (LE) (P5.393)

Objective:

1. Underscore increasing recognition of LGI-1 encephalitis as a cause of LE

2. Report two cases of Anti-LGI-1 encephalitis that presented without the pathognomonic Fascio-Brachial Dystonic Seizures (FBDS)

3. Consider modified diagnostic criteria for anti-LGI-1 Encephalitis.

Background: LGI-1 is a trans-synaptic modulator protein that was first identified in 2010 as a target in anti-VGKC autoimmune encephalitis. Anti-LGI-1 encephalitis is now the most common cause of LE (subacute behavioural disturbance, memory loss and focal seizures) amongst the anti-neuronal-cell-surface antibody encephalitides. The relative occurrence of four clinical/laboratory features that are most sensitive for Anti-LGI-1 encephalitis include [1]presenting-as-LE(90%) [2]Bi-temporal-T2-hyperintensities(74%) [3]hyponatremia(65%) [4]normal CSF study(75%). Alhough FBDS is a pathognomonic feature of Anti-LGI encephalitits it is only seen in upto 40% cases.

Design/Methods: Case Report

Results: We report 2 cases of CSF-antibody positive Anti-LGI-LE without the pathognomonic FBDS. First was was a 35-year-old-woman who presented with 3 weeks of confusion, memory loss and auditory hallucinations, found to have bi-temporal-T2-hyperintensities and a normal EEG study. The second was a 79-year-old-man with 2 weeks of confusion and memory loss who developed a generalised tonic clonic seizure, found to have multiple brief right temporal focal seizures on EEG with an unremarkable MRI brain. Their work up showed normal serum, CSF studies except for mild hyponatremia and were suspected to have Anti-LGI1 encephalitis based on the presence of 3 out of the above 4 features with subsequently positive Anti-LGI1 antibodies detected in the CSF of both patients.

Conclusions: Majority of patients with Anti-LGI1 encephalitis will not develop FBDS as noted in our cases. We propose that presence of 3 out of the above 4 features makes anti-LGI-1 encephalitits a likley diagnosis even in the absence of FBDS. Further studies are required to evaluate the sensitivity and specificty of these modified criteria.

Disclosure: Dr. Topiwala has nothing to disclose. Dr. Patel has nothing to disclose. Dr Datta has nothing to disclose. Dr. Zhang has nothing to disclose. Dr. Silverman has nothing to disclose.