Supplementary Material for: Successful Plasma Exchange and Steroid Maintenance Therapy for Severe Pembrolizumab-Induced Polyradiculoneuritis in Lung Cancer: A Case Report

Introduction: Neurological immune-related adverse events (n-irAEs) caused by immune checkpoint inhibitors (ICIs) are rare but can be life-threatening. Case Presentation: A 43-year-old man with stage IVB squamous cell carcinoma of the lung developed progressive polyradiculoneuropathy 180 days after the first pembrolizumab administration. Initial treatments with high-dose corticosteroids and intravenous immunoglobulin (IVIg) were ineffective. Cerebrospinal fluid (CSF) analysis revealed albuminocytologic dissociation, and magnetic resonance imaging (MRI) revealed cervical nerve root hypertrophy. Plasma exchange (PE) was initiated along with steroid maintenance, resulting in gradual neurological recovery, as evidenced by improvements in the MRC score (from 32 to 56, on a scale from 0 to 60, with higher scores indicating greater muscle strength) and resolution of MRI abnormalities. Tumor control was sustained throughout the treatment. Conclusion: This case highlights the potential efficacy of combining plasma exchange and steroid maintenance therapy in managing severe, refractory n-irAEs without compromising oncologic outcomes.