In the context of an increasing repertoire of multiple sclerosis (MS) therapeutics, choosing the appropriate treatment for an individual patient is becoming increasingly challenging. Natalizumab, a humanized monoclonal antibody directed against alpha4beta1 integrin, has proven short-term and long-term efficacies in terms of relapse rate reduction, prevention of disability progression, and reduction of magnetic resonance imaging-detectable activity. It is well tolerated and has further been shown to improve patients' quality of life. Its use is limited by the risk of progressive multifocal leukoencephalopathy (PML), which occurs at an overall incidence of 3.78 cases per 1,000 patients. Three major risk factors for the occurrence of natalizumab-associated PML have been identified: John Cunningham virus (JCV) seropositivity, prior use of immunosuppressants, and treatment duration ≥2 years. Therefore, in patients considered for natalizumab therapy, as well as in patients receiving natalizumab, effective control of MS activity has to be balanced against the risk of an opportunistic central nervous system infection associated with a high risk of significant morbidity or death. Discontinuation of natalizumab is an issue in daily clinical practice, since it is an option to reduce the PML risk. However, after cessation of natalizumab therapy, currently, there is no approved strategy for avoiding postnatalizumab disease reactivation available. In this paper, short-term and long-term safety and efficacy data are reviewed. Issues in daily clinical practice, such as selection of patients, monitoring of patients, and natalizumab discontinuation, are discussed.
Keywords: PML; adherence; long-term outcome; pediatric multiple sclerosis; safety; treatment discontinuation.