Anyone ever heard of the saying that a little knowledge is a dangerous thing?

The release of the limited data on the PML cases provides for wonderful speculation from non-scientifically trained financial analysts and armchair statisticians but provides little insight into what the risk factors for developing PML are. Limited snapshots of the case data have suggested wildly different things. The first reported cases were clustered between 12 and 18 months. Since that time, we've seen no new cases in that treatment period even though the patients exposed in that timeframe has grown significantly. Now with a clustering of cases over 24 months of treatment, everyone's rushing to the conclusion that its treatment duration related. That could turn out to be a factor but it could just as easily be something else.

All we really know for certain based on what's in the public domain is that Tysabri treatment can lead to PML, PML can be clinically diagnosed early, and identified interventions can lead to better PML outcomes.