EU watchdog assessing Tysabri brain disease cases

LONDON Aug 13 (Reuters) - The European Medicines Agency said on Wednesday it was assessing two cases of a potentially deadly brain disease reported last month in multiple sclerosis (MS) patients being treated with the drug Tysabri.

The London-based agency said it would then decide whether any changes were necessary to the currently approved label for product, which is made by Elan Corp Plc (ELN.I) and Biogen Idec Inc (BIIB.O).

Shares in both companies slumped following the July 31 news of the latest cases of the brain infection known as progressive multifocal leukoencephalopathy (PML).

Tysabri was withdrawn from the market in 2005 after three patients developed PML. It returned in 2006 but the latest cases may prompt physicians to reduce the number of patients they start on the drug, analysts fear.

More than 31,800 patients were being treated with Tysabri as of the end of June and second-quarter sales totaled $200 million. (Reporting by Ben Hirschler; Editing by Paul Bolding)