Paradoxical Tumefactive Worsening of Multiple Sclerosis After Natalizumab Initiation: A Case Report

Background: Natalizumab is a widely used anti-α4 integrin inhibitor for treating highly active multiple sclerosis. Although clinical and radiological relapses were observed in the pivotal natalizumab trials, severe disease activity after initiation of drug rare phenomenon has been reported only isolated cases. Objective: To present case patient who experienced paradoxical increase second dose natalizumab. Methods: We describe case, review literature concerning similar cases suggest possible mechanisms this phenomenon. Results: Our involves developed extensive tumefactive demyelinating lesions gadolinium-enhancing detected on magnetic resonance imaging receiving A brain biopsy confirmed presence demyelination, patient’s condition improved treatment with intravenous methylprednisolone, immunoglobulin plasma exchange. Tests anti-natalizumab antibodies negative. Conclusions: Paradoxical worsening can occur setting treatment, which warrants careful attention should prompt antibody testing. discuss potential mechanisms. Further research needed to better understand risk factors develop strategies mitigating adverse effect significant impact.