Natalizumab is effective in controlling the inflammatory rebound after its discontinuation and failure of an alternative treatment.

Progressive multifocal leukoencephalopathy (PML) is the most feared complication when natalizumab (NAT) is used in the treatment of relapsing multiple sclerosis (MS). JC virus serologic status is a currently established risk factor for PML. When seroconversion occurs, NAT discontinuation should be based on a solid rationale to avoid an MS inflammatory resurgence. The JC virus index value may also provide further useful information to help practitioners and patients in their decision process.