Time is brain for infections too?

Progressive multifocal leukoencephalopathy (PML) is a serious neurologic condition caused by the JC virus, which generally develops in chronically immunosuppressed patients. The emergence of this devastating disease in the setting of natalizumab therapy for multiple sclerosis (MS) has challenged neurologists.¹ Better therapy for MS is urgently needed, and clinical trials suggest that natalizumab can markedly reduce the magnetic resonance–demonstrated activity associated with MS, as well as slow progression of disability.^2,3 Sadly, a very significant risk of PML is now clearly associated with use of this therapy. Neurologists must gather the needed information to honorably carry out their task of framing therapeutic choices for patients, as well as coming to terms with when they recommend such a therapy. While therapies including lethal complications are commonly used in other disciples of medicine such as oncology and surgery, they have been rare in neurology. At a minimum, neurologists require data concerning potential benefits, the frequency of serious complications, and severity of outcomes if the complications are encountered. Clinical trials with natalizumab suggest that it provides a significant benefit to MS control, although direct head-to-head comparisons with …