Severe relapses after the first infusion of natalizumab in active relapsing-remitting multiple sclerosis.

We describe three patients suffering from a very active form of relapsing-remitting multiple sclerosis (MS), who experienced severe disease worsening, associated with a marked increase in brain inflammation, a few days after the first administration of natalizumab. In line with preclinical studies, our observations suggest that natalizumab, when administered during active disease phases, may worsen disease evolution possibly by modifying the regulatory network in the brain. We suggest that relapsing-remitting MS patients having had a recent relapse should be treated with natalizumab only after achieving complete clinical and radiological remission.