The well-respected New England Journal of Medicine published case reports on all three of the Tysabri PML patients today. The reports go into great detail on how PML developed. Alongside them are editorials by Joseph Berger and Igor Koralnik, two of the world's top experts in PML, who work as consultants for Biogen Idec and Elan. In a rather blunt conclusion, the two write that the linkage between the drug and PML, though unexpected is rather clear. However, they also write that it may be possible to detect the proliferation of the PML-causing JC virus before much of the damage is done, and then stop Tysabri treatment. They leave the question open as to whether the Food and Drug Administration will require new trials to prove that PML is haltable. It is important to note that most PML cases prior to the Tysabri situation were in patients with HIV that were inherently immuno-compromised. Patients taking Tysabri, on the other hand, are artificially immuno-suppressed and so it makes sense that removing the treatment removes the conditions allowing PML to develop.
Another interesting "discovery" was that for the patient that survived (on Tysabri + Avonex) it took approximately 3 months for Tysabri's effect to wear off after the last dose. Surprisingly, there is no discussion about the fact that this could be related to the fact that co-administration of Tysabri with Avonex has been shown to reduce the clearing of Tysabri from the body versus Tysabri monotherapy.
"Unfortunately, we know little about PML and JC
virus, but important observations can be gleaned
from these case reports. One report suggests that
clinical PML may be preceded by JC viremia.
Another demonstrates that PML is not uniformly fatal. It is possible that testing for the appearance of JC virus in plasma, along with a high degree of clinical suspicion, will permit early diagnosis and discontinuation of natalizumab therapy and allow patients to recover. Similar findings have been reported for BK virus, a related polyomavirus that infects transplant recipients."
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Link to NEJM Articles
New England Journal of Medicine Articles on Tysabri and PML
