BOSTON, April 20 (Reuters) - A sixth patient taking Biogen Idec Inc's (BIIB.O) multiple sclerosis drug Tysabri has developed a potentially deadly brain infection since the drug was reintroduced onto the market in July 2006.
The Cambridge, Massachusetts-based biotech company announced the news late on Friday on its website, saying the case was confirmed on April 15th.
Biogen has said it does not plan to announce each new case of progressive multifocal leukoencephalopathy, or PML, except as a weekly update on its website.
Even so, the confirmation occurred a day before Biogen's first-quarter earnings conference call, and some analysts questioned why the company did not mention it.
"While we applaud management's decision to update PML cases weekly, we think it's fair to ponder why this wasn't fully discussed on the earnings call," said Christopher Raymond, an analyst at Robert W. Baird, in a research note.
A spokeswoman for Biogen was not immediately available for comment.
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