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Longitudinal monitoring of JCV antibodies as an aid in diagnosing of PML?
Patients treated with natalizumab for active relapsing–remitting multiple sclerosis (MS) benefit from its high efficacy and excellent tolerability; this was shown in the pivotal studies1 ,2 and has been confirmed by several prospective and retrospective observational studies in real-life settings.3 ,4 Though, treated patients and prescribing physicians alike are threatened by the low but over the years increasing risk of progressive multifocal leucoencephalopathy (PML). As of 2 January 2013, worldwide statistics of the manufacturer documented 323 confirmed cases out of approximately 108 300 patients with MS and Crohn's disease exposed to natalizumab. Although natalizumab-associated PML is less frequently lethal, most of the affected patients develop severe and permanent disability that adds to the burden of MS.5 A more favourable prognosis is clearly related to an early detection of PML and reconstitution of immune surveillance. Therefore, there is obviously a high need for reliable risk stratification, early detection and, if possible, prevention of PML.
Detection of anti-John Cunningham virus (JCV) antibodies in the blood has been proposed as the strongest risk predictor based on large studies allowing to predict a risk of less than 0.09 in 1000 patients negative for anti-JCV, and a risk of 2.86–4.96 per 1000 patients for those who have detectable levels of Abs against JCV with or without additional risk factors (duration of treatment, previous exposure to …