Background: Multiple sclerosis (MS) is a common, chronic, inflammatory disease of the central nervous system (CNS), which primarily affects young people. There exists no causal treatment as the disease is not fully understood. The most effective medication available today is natalizumab, a monoclonal antibody which is supposed to prevent the inflammatory cells to cross the blood-brain barrier and causing demyelinisation. Reported causes of progressive multifocal leukoencephalopathy (PML) as a side effect have made natalizumab a controversial medication. The aim of this study is to give an overview of what the current literature tells about the evidence based effect according to the rate of clinical relapse and disease activity detected on MRI, and the risk of developing PML as a side effect.
Method: The text is based on information found through a systematic search in PubMed and Cochrane Library for articles published in Neurology, Lancet and New England Journal of Medicine.
Results: The AFFIRM study showed that the relative reduction of the rate of clinical relapse was 68%. Gd-enhanced MRI showed a 92% reduction of lesions in the natalizumab group compared to the placebo group. T2-weighted MRI showed a 83% reduction in the accumulation of new or enlarging hyperintense lesions. The calculated risk for developing PML is estimated to 1:1000. Until today (Dec 2009) 63300 patients have been on natalizumab and there have been 30 registered causes of PML, 7 of fatal outcome.
Conclusion: Existing research on this medication is limited, but shows a significant efficacy according to reduced number of clinical relapses and disease activity detected on MRI as monotherapy in relapsing-remitting multiple sclerosis. The risk is low, but developing PML as a side effect is still the limiting factor according to the potentially fatal outcome. More research is needed on long-term effect and safety.