Movement-Provoked Paroxysmal Neuralgia Following Longitudinally Extensive Transverse Myelitis in Neuromyelitis Optica Spectrum Disorder: A Presumed Ephaptic Spinal Cord Phenomenon.

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune astrocytopathy frequently complicated by neuropathic pain. Paroxysmal symptoms likely arise from ephaptic transmission within demyelinated spinal cord tracts and are underdescribed when presenting as isolated sensory phenomena, unlike the well-characterized tonic spasms. We report a 76-year-old woman with aquaporin-4 (AQP4) antibody-positive NMOSD recovering from her first disease flare, which initially manifested as longitudinally extensive transverse myelitis (LETM). Weeks later, she developed sudden, excruciating, movement-provoked paroxysmal burning pain in the lower extremities. Episodes lasted 4-8 seconds and occurred approximately 20 times daily. Serial neurologic examinations revealed no new deficits suggestive of relapse, and repeat MRI was deferred as relapse was considered clinically unlikely. Symptoms were refractory to gabapentin but improved dramatically within 24 hours of initiating oxcarbazepine 300 mg twice daily. The clinical phenotype and rapid response to sodium channel blockade support a sodium channel-mediated mechanism, most likely ephaptic transmission, rather than trigger-independent ectopic firing, which remains sparsely described in the literature. Recognition of this phenomenon is crucial to avoid misclassification as relapse, unnecessary imaging, and unwarranted escalation of immunotherapy.