The first person had an aggressive form of MS and had been taking Tysabri for approximately 17 months. They are now in a stable condition at home. The second person had taken Tysabri for around 14 months and is currently in hospital. Possible signs and symptoms of PML were identified through the risk management program which monitors for signs of the condition.

As of the end of June 2008 more than 31,800 people worldwide are being treated with Tysabri. The two new cases of PML were confirmed at the end of July 2008, bringing the total of people who have developed PML to five.

Lee Dunster, Head of Research at the MS Society, said: 'We know the reports of two new cases of PML will be of some concern to people who are taking the drug, however we would reassure people that the risk of developing these serious side effects remains very small. As with all treatments, the benefits must be weighed with the risks of side effects and these issues should be discussed fully between you and your doctor.'

http://www.medicalnewstoday.com/articles/117121.php