What's different about teratoma-associated anti-LGI1 encephalitis? A long-term clinical and neuroimaging case series

Background Anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis is clinically heterogeneous, especially at presentation, and though it is sometimes found in association with tumor, this is by no means the rule. Methods Clinical data for 10 people with anti-LGI1 encephalitis and 3 people with anti-N-Methyl-D-aspartate receptor (NMDAR) encephalitis with teratoma were collected. Microscopic pathological examination and immunohistochemical (IHC) assay of the LGI1 antibody were performed on teratoma tissue obtained by laparoscopic oophorocystectomy. Results In our teratoma associated anti-LGI1 encephalitis case, teratoma pathology was characterized by mostly thyroid tissue and IHC assay confirmed partial or focal positive nuclear staining of LGI1 in some tumor cells. The case was similar to the non-teratoma (NT) group in many ways: age at onset; percent presenting with rapidly progressive dementia (RPD) and psychiatric symptoms; hyponatremia; normal cerebrospinal fluid (CSF) results except for positive LGI1 antibody; bilateral hippocampal hyperintensity on magnetic resonance imaging (MRI); diffuse slow waves on electroencephalogram (EEG); good response to immunotherapy and mild residual cognitive deficit. Her chronic anxiety and status epilepticus (SE) were the biggest differences compared with NT group. Interestingly, the case presented many differences compared with anti-NMDAR encephalitis with teratoma: older onset age, prominent anxiety, SE, hyponatremia, normal CSF cell count, hippocampal hyperintensity on MRI and slowly recovered and residual short-term memory impairment. Conclusion In our series, anti-LGI1 encephalitis included common clinical features: RPD, faciobrachial dystonic seizures, behavioral disorders, hyponatremia, T2-MRI hyperintensity of hippocampus and residual cognitive deficit, but a larger accumulation of cases is needed to improve our knowledge base.