Longitudinal Extensive Myelitis After Measles in a Behçet's Disease Patient: Post-infectious Trigger or Neuro-Behçet?

Longitudinally extensive transverse myelitis (LETM) encompasses a group of demyelinating pathologies with diverse etiologies. We report a rare case of LETM in a patient with Behçet's disease, occurring shortly after a confirmed measles infection. This case raises a diagnostic and therapeutic dilemma between post-infectious and autoimmune causes. A 37-year-old woman with stable Behçet's disease developed progressive lower limb weakness two days after a measles-like exanthem. Neurological examination revealed paraparesis and a sensory level at the manubrium. Spinal MRI demonstrated a longitudinally extensive cervico-thoracic lesion with a characteristic "bagel sign." Measles serology showed positive IgM and IgG, confirming a recent primary infection. The patient was treated with intravenous methylprednisolone followed by tapering oral corticosteroids, resulting in marked clinical and radiological improvement. This case highlights the diagnostic complexity of myelitis in patients with coexisting autoimmune conditions and recent viral infection. The favorable response to corticosteroids alone, without the use of immunosuppressive agents, supports a post-infectious etiology. This report underscores the need for individualized therapeutic decisions and the ongoing importance of maintaining high vaccination coverage.