Case Report: Observational use of mycophenolate mofetil in probable steroid-unresponsive immune checkpoint inhibitor-associated transverse myelitis.

Immune checkpoint inhibitor (ICI)-associated transverse myelitis (TM) is a rare and severe neurological immune-related adverse event (n-irAE) with an incidence of < 0.01%, and the clinical management of steroid-unresponsive cases remains extremely challenging. This article reports the case of a 37-year-old male patient with biphasic pleural mesothelioma who developed ICI-associated TM after treatment with nivolumab combined with ipilimumab. Initial treatment with high-dose glucocorticoids plus intravenous immunoglobulin (IVIg) was ineffective. After mycophenolate mofetil (MMF) was added in combination with steroids for 1 month, the patient's neurological function showed slight improvement, and intramedullary contrast-enhanced signals on spinal MRI showed partial reduction. However, spinal cord cystic or myelomalacic changes suggested potentially irreversible parenchymal injury. Currently, the patient has restarted pemetrexed combined with carboplatin chemotherapy, and the disease status is stable. Based on recently published case series, case reports, and systematic reviews, this article discusses the second-line treatment strategies for steroid-unresponsive ICI-associated TM, aiming to provide a reference for clinical practice in managing such rare cases.