Four Tysabri patients have died from a rare brain disease, progressive multifocal leukoencephalopathy (PML), since the drug returned to the market in July 2006.

Details of the fatalities emerged yesterday from the European Medicines Agency.

The four are among 24 PML cases diagnosed since July 2006, the agency said.

That figure, confirmed by the US Food and Drug Administration yesterday, indicates an additional case has emerged since the agency disclosed last Friday that it was reviewing the risks and benefits of the drug on the back of the rising incidence of PML. Before last week, only 13 cases of PML in Tyasbri patients had been disclosed by the companies.

Biogen had conceded earlier that week that it had confirmed a link between the length of time a patient was on Tysabri and the risk of contracting PML.

Medicines agency spokeswoman Vladimira Yalmanova said that, since the drug was reintroduced to the market in 2006, 16 of the cases were found in Europe, including two in Switzerland, and eight were in the US.