June 9, 2005 According to Biogen Idec, multiple sclerosis patients might be able to take Tysabri safely, provided they also periodically test their blood for the presence of the progressive multifocal leukoencephalopathy (PML) virus. A blood test of a patient taking Tysabri in a Crohn’s disease trial showed the presence of the virus three months before the disease developed. Theoretically, by monitoring their condition, multiple sclerosis patients could continue to enjoy the benefits of Tysabri, while making sure they weren’t developing PML, for which there is no cure. We look at this, the newest twist in this ongoing saga...