Pembrolizumab-Induced High Inflammatory Panmyelitis: Contribution of Neurochemical Markers Predicting Severity of Central Nervous Affection

This is the first documented case of recurrent, severe, and highly inflammatory panmyelitis induced by pembrolizumab. A 41-year-old woman with nodular melanoma developed tetraparesis after three cycles of pembrolizumab treatment. Spinal magnetic resonance imaging (MRI) revealed extensive longitudinal panmyelitis, and cerebrospinal fluid analysis showed markedly elevated cell counts (3900/mm3). Follow-up measurements of neurofilament light chain (NfL) levels correlated with the severity of central nervous system involvement and reflected clinical, radiological, and biochemical progression. The clinical outcome was surprisingly favorable following treatment with intravenous immunoglobulins (IVIG) and corticosteroids.