• Biomarker levels of leucine rich glioma inactivated 1 associated encephalitis [ Time Frame: 3 months ]
  Core CSF biomarkers (T-tau, P-tau, Amyloid β Protein Fragment 1-42 (AB1-42), AB1-40, Neurofilament light chain, in ng/L) will be assessed in LGI1-E patients and will be compared to the profile of patients presenting with common and rapid Alzheimer's disease and with Creutzfeldt Jacob disease (CJD). For each biomarker, statistical comparisions will be made by Kruskal Wallis test then if needed with Wilcoxon Mann Whitney test.
• Biomarker levels of anti leucine rich glioma inactivated 1 associated encephalitis [ Time Frame: 3 months ]
  Neopterin Cerebrospinal Fluid (CSF) levels (nanomole/Liter, nmol/L) will be assessed in anti Leucine-rich Glioma inactivated-1 Encephalitis (LGI1-E) patients.
• Biomarker levels of anti leucine rich glioma inactivated 1 associated encephalitis [ Time Frame: 3 months ]
  Prion protein Cerebrospinal Fluid (CSF) levels (ug/L) will be assessed in LGI1-E patients

• Comparison of biomarker profile (T-tau, P-tau, Amyloid β Protein Fragment 1-42 (AB1-42), AB1-40, Neurofilament light chain, in nanograms/Liter (ng/L) [ Time Frame: two weeks ]
  Statistical comparisons of CSF biomarker levels of patients presenting with anti leucine rich glioma inactivated 1 associated encephalitis with or without epileptic seizures. Mean comparisons will be made for each biomarker, with the Wilcoxon Mann Whitney test.
• Comparison of biomarker profile in anti leucine rich glioma inactivated 1 associated encephalitis (LGI1-E) with versus without faciobrachial dystonic seizures. [ Time Frame: two weeks ]
  Statistical comparisons of CSF biomarker levels of patients presenting with anti leucine rich glioma inactivated 1 associated encephalitis (LGI1-E) with or without faciobrachial dystonic seizures. Mean comparisons will be made for each biomarker, with the Wilcoxon Mann Whitney test.

Limbic encephalitis associated with anti leucine-rich glioma inactivated-1 LGI1 antibody (anti-LGI1) usually presents with seizures and progressive disturbance of memory and behavior. But anti-LGI1 associated encephalitis (LGI1-E) could present with a variety of features including an elective cognitive form of the disease, which mimicks a neurodegenerative condition such as Creutzfeld Jakob disease or rapidly progressive Alzheimer disease. In these patients, the appropriate diagnosis could be challenging.

The primary aim of this study is to describe cerebrospinal fluid biomarkers in a cohort of LGI1-E patients as results of these markers are currently not described in LGI1-E. Moreover, patients with LGI1-E often present seizures. At this point, the impact on cerebrospinal fluid biomarkers has not been described in this condition. The secondary aims of this study are to compare cerebrospinal fluid (CSF) biomarkers in LGI1-E patients to these in other neurodegenerative conditions ( e.g. creutzfeld Jakob disease, Alzheimer disease), which are considered as a possible differential diagnosis in these patients. The last aim of this study is to look for correlations between cerebrospinal fluid biomarkers in LGI1-E and clinical data in these patients, especially seizure.

• Encephalitis
• LGI1 Antibody Associated Encephalitis

Inclusion Criteria:

• Presence of well characterized leucine rich glioma inactivated 1 (LGI1) antibody in serum or cerebrospinal fluid (CSF);
• LGI1 antibody associated encephalitis diagnosis according to the international guidelines;
• At least one core CSF biomarkers sample (T-tau, P-tau, AB-1-42) available after disease onset;
• Age at least 18 years old.

Exclusion Criteria:

• Absence of clinical data