Olfactory Hallucinations as the Initial Symptom of Anti-Leucine-Rich Glioma-Inactivated 1 Antibody Encephalitis: A Case Report and Review of the Literature.

Anti-leucine-rich glioma-inactivated 1 (LGI-1) antibody encephalitis is an autoimmune encephalitis mediated by LGI-1 antibodies that target proteins on the surface of neuronal cell membranes. Its clinical manifestations are diverse, but olfactory hallucinations rarely present as the initial symptom. We report the case of a 61-year-old man who initially presented with olfactory hallucinations and abdominal discomfort lasting six months. This was rapidly followed by memory impairment, twitching at the right corner of the mouth, and upper limb spasms. A follow-up brain MRI scan revealed abnormal signals in the bilateral hippocampi, and both serum and cerebrospinal fluid (CSF) tests were positive for LGI-1 antibodies, leading to a diagnosis of anti-LGI-1 antibody-associated encephalitis. Following high-dose steroid pulse therapy, the patient achieved complete remission of symptoms. This report suggests that olfactory hallucinations may be an early manifestation of the disease involving the parahippocampal gyrus and the uncus. In middle-aged men presenting with new-onset olfactory hallucinations or similar symptoms, antibody screening should be performed as early as possible.