Case Report: Anti-AMPAR A1 Autoimmune Encephalitis Following Resection of Multifocal Early-Stage Lung Adenocarcinoma with Exploratory Immunohistochemical Insights

Background: Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) autoimmune encephalitis is a rare antibody-mediated inflammatory disorder of the central nervous system. Approximately half of reported cases are associated with underlying neoplasms, most commonly thymoma, small-cell lung cancer, and breast cancer. However, its association with lung adenocarcinoma, particularly at an early stage, remains rarely described Case Presentation: We report the case of a 38-year-old woman who developed subacute memory impairment approximately six months after undergoing video-assisted thoracoscopic wedge resection for multifocal pulmonary ground-glass nodules. Cerebrospinal fluid (CSF) analyses revealed anti-AMPAR A1 antibody positivity (titer 1:10). Cranial magnetic resonance imaging (MRI) showed no significant abnormalities. The patient demonstrated marked clinical improvement following high-dose intravenous methylprednisolone therapy. To explore a potential paraneoplastic mechanism, exploratory immunohistochemical (IHC) staining for AMPAR A1 was performed on the previously resected lung specimens, revealing scattered, weak cytoplasmic immunoreactivity in a subset of tumor cells. Conclusion: This case raises the possibility of an association between early-stage lung adenocarcinoma and anti-AMPAR A1 autoimmune encephalitis. The IHC findings provide preliminary histological clues suggestive of AMPAR-related immunoreactivity in tumor tissue; however, further studies are required to clarify the underlying mechanisms.