Pembrolizumab-induced aseptic meningitis in a patient with non-small cell lung cancer: A case report and literature review of aseptic meningitis as an immune-related adverse event.

Aseptic meningitis is a rare immune-related adverse event (irAE), which occurs during treatment with immune checkpoint inhibitors (ICIs). This condition has non-specific symptoms and exhibits no clear signs on magnetic resonance imaging (MRI). There are only a few reports of aseptic meningitis caused by pembrolizumab treatment for non-small cell lung cancer (NSCLC). The present study includes a report of such a case and a review of the related literature. A 67-year-old Japanese man received first-line pembrolizumab treatment for NSCLC and subsequently developed severe nausea and vomiting. No significant findings were observed following a computed tomography (CT) scan, MRI of the brain and upper gastrointestinal tract, or upper gastrointestinal endoscopy. Cerebrospinal fluid analysis revealed lymphocyte infiltration and elevation of the IgG index, without indications of metastasis or infection, which suggested the presence of aseptic meningitis. The symptoms immediately improved following prednisolone treatment, and aseptic meningitis was diagnosed as an irAE related to pembrolizumab treatment. Given that aseptic meningitis can cause non-specific symptoms, including headache and nausea, the possibility of an irAE should be considered in patients with non-specific symptoms who are receiving ICIs, and a cerebrospinal fluid examination should be performed.