Anti-LGI1 antibody-positive autoimmune encephalitis concurrent with neuropsychiatric systemic lupus erythematosus.

Anti-leucine-rich glioma-inactivated protein 1 (LGI1) antibody-positive limbic encephalitis is a form of autoimmune encephalitis (AE). The importance of anti-LGI1 antibody in neuropsychiatric systemic lupus erythematosus (NPSLE) remains unclear. We present a 65-year-old woman with amnesia and disorientation, positive anti-LGI1 and anti-Smith antibodies, hyponatremia, leukopenia, and hypocomplementemia. Magnetic resonance imaging findings were consistent with limbic encephalitis and cervical myelitis. She was diagnosed with NPSLE with anti-LGI1-positive AE. High-dose glucocorticoids and intravenous cyclophosphamide led to sustained remission. This case suggests that NPSLE may coexist with anti-LGI1-positive AE, highlighting the potential importance of anti-LGI1 antibody testing in NPSLE and expanding the management of AE.