August 2012 Tysabri PML update that was made available to physicians:

As of August 1, 2012, there have been 271 PML cases, of which 162 have been in the European Economic Area (EEA), 97 in the US and 12 in rest of world (ROW).

As of August 1, 2012, 59 of the 271 patients with PML have died.

As of August 1, 2012, in 85 natalizumab-treated MS patients who developed PML and for whom serum samples were available 6-187 months prior to the onset of PML. Of these 85 patients:

83 (98%) tested anti-JCV antibody positive at all time points where samples were available for testing;

1 patient (1%) tested anti-JCV antibody negative 9 months prior to PML diagnosis and anti-JCV antibody positive 6.5 months prior to PML diagnosis;

1 patient (1%) tested anti-JCV antibody negative 9 months prior to PML diagnosis; no additional samples were available.

As of August 1, 2012, samples were available from 112 patients at the time of PML diagnosis and all 112 tested positive for anti-JCV antibodies.

In addition, one sample, collected from a patient at the time of PML diagnosis following a cycle of plasma exchange (PLEX) tested negative for anti-JCV antibodies.

Because this sample was collected immediately following PLEX, and PLEX removes antibodies from the circulation, the information obtained from this sample is unreliable.

One patient tested anti-JCV antibody positive two months before PML diagnosis. Previously, the patient had tested anti-JCV antibody negative 15 months prior to PML diagnosis, indicating that they had been exposed to the JC virus at some point between the two tests.

Source: Elan (20/08/12)