In this sample of 20 patients with anti-LGI1 encephalitis and a 100% rate of anti-LGI1-IgG4 serum antibodies, the additional presence of potentially complement activating anti-LGI1-IgG1/2/3 was the only factor that was associated with HS and reduced hippocampal volumes according to the initial hypotheses. This evidence concerns the gene LGI1 and histiocytic sarcoma.