Biogen flags sixth case of PML

Biogen Idec reported a sixth case of the potentially fatal brain disease progressive multifocal leukoencephalopathy, or PML, in a multiple sclerosis patient taking its drug Tysabri. According to Dow Jones, about 40,000 patients were using Tysabri at the end of the first quarter, and 24,900 of them have used the drug for a year or more. Report