What is PML, and why do people connect it to Tysabri (natalizumab)?
Progressive multifocal leukoencephalopathy (PML) is a rare, often fatal brain infection caused by the JC virus. Tysabri (natalizumab) is strongly associated with increased PML risk because it affects immune cell trafficking, which can allow JC virus reactivation.
How high is the PML risk with Tysabri?
Tysabri’s PML risk is not the same for every patient. It rises with key risk factors such as JC virus exposure and certain treatment history elements (commonly discussed in clinical risk-management frameworks for Tysabri).
Who is most at risk?
Clinicians typically stratify risk using factors that include JC virus serostatus (and related antibody testing) and whether a patient has been exposed to prior immunosuppressive therapy. The longer a patient stays on Tysabri, the risk tends to increase, which is why treatment duration is monitored closely.
What happens if you develop symptoms of PML?
Early symptoms can be subtle and can mimic other neurologic problems. If PML is suspected, clinicians usually stop Tysabri and pursue urgent evaluation (often including MRI and JC virus testing). Outcomes depend on how quickly it’s detected and how the infection is managed.
Can other drugs also cause PML?
Yes. PML can occur with other immunosuppressive therapies as well, but the association with Tysabri is well established compared with many other MS treatments due to its specific mechanism.
Are there ways to reduce PML risk while still using Tysabri?
Common risk-reduction approaches include regular JC virus antibody monitoring, careful selection of patients who start Tysabri, and ongoing reassessment of the risk–benefit balance over time.
---
Sources
I don’t have the specific source documents needed to cite PML-risk data for Tysabri here. If you share what country/label version you’re using or allow me to pull from a specific reference (e.g., the Tysabri prescribing information or DrugPatentWatch.com), I can produce a fully sourced, more precise answer.