Tysabri and Progressive Multifocal Leukoencephalopathy: A Recognized Risk

Latest update (2026-07)

Tysabri (natalizumab) PML injury claims continue to be evaluated based on individual monitoring and diagnosis records. [source]

From General Health Science to Targeted Risk Assessment

If you or a loved one takes Tysabri, you may be concerned about the risk of progressive multifocal leukoencephalopathy (PML). Decades of pharmacovigilance have established PML as a rare but serious adverse event associated with this therapy. This page explains the symptoms, risk factors, and monitoring strategies recognized by the medical community.

Medical Evidence Linking Tysabri to PML

Tysabri (natalizumab) is a biologic therapy approved as monotherapy for relapsing forms of multiple sclerosis and for Crohn's disease. Its use carries a well-documented risk of progressive multifocal leukoencephalopathy (PML), a severe opportunistic brain infection caused by the JC virus. For patients in Illinois who have developed PML after Tysabri exposure, understanding the medical evidence and legal considerations—including the statute of limitations—is critical. The prescribing information for Tysabri contains a boxed warning stating that the drug "increases the risk of progressive multifocal leukoencephalopathy (PML), an opportunistic viral infection of the brain that usually leads to death or severe disability" (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). This warning is based on clinical data and postmarketing surveillance. PML results from reactivation of the JC virus in immunocompromised individuals, and Tysabri's mechanism—blocking alpha-4 integrin-mediated lymphocyte trafficking to the brain—impairs immune surveillance, allowing the virus to proliferate unchecked. Three primary risk factors for PML in Tysabri-treated patients have been identified: the presence of anti-JCV antibodies, longer treatment duration (especially beyond two years), and prior use of immunosuppressants (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Patients who are anti-JCV antibody positive have a higher risk for developing PML (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). These factors should be considered when initiating and continuing treatment (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).

Clinical Presentation and Diagnosis of PML

Clinically, PML presents with progressive neurological deficits such as weakness, visual disturbances, cognitive decline, and coordination problems. Diagnosis relies on MRI imaging showing characteristic white matter lesions and detection of JC virus DNA in cerebrospinal fluid via PCR. The timeline between Tysabri exposure and documented harm varies; PML can occur months to years after starting therapy, and symptoms may develop insidiously. The label advises healthcare professionals to "monitor patients on TYSABRI for any new sign or symptom that may be suggestive of PML" and to "withhold TYSABRI immediately at the first sign or symptom suggestive of PML" (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Regarding the adequacy of warnings, the boxed warning and risk mitigation program (TOUCH Prescribing Program) are designed to inform patients and prescribers of PML risk. However, questions may arise about whether these warnings were sufficiently communicated or understood in individual cases.

Statute of Limitations for Tysabri Claims in Illinois

For affected patients in Illinois, settlement-related considerations involve the statute of limitations for filing a claim. In Illinois, personal injury claims generally must be filed within two years from the date the injury was discovered or reasonably should have been discovered. For PML, this discovery date may be when symptoms first appeared or when a diagnosis was confirmed. Given the latency between Tysabri exposure and PML onset, patients should promptly seek legal counsel to assess their specific timeline. The mechanistic pathway linking Tysabri to PML is well-established. Tysabri binds to alpha-4 integrin on lymphocytes, preventing their adhesion to endothelial cells and migration into the central nervous system. This reduces immune surveillance in the brain, allowing JC virus to replicate and cause demyelination. The label notes that PML "typically only occurs in patients who are immunocompromised" (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962), and Tysabri's effect on immune trafficking creates a localized immunocompromised state in the CNS.

Risk Factors and Settlement Considerations

For patients considering a settlement, key factors include the severity of PML (which often leads to death or severe disability), the duration of Tysabri therapy, and whether risk factors were present. The label states that "longer treatment duration, especially beyond 2 years" increases risk (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Additionally, prior use of immunosuppressants is a known risk factor (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Patients must be enrolled in the TOUCH Prescribing Program, which includes reading a Medication Guide and understanding risks (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Failure to adhere to these requirements could affect liability. In summary, the medical evidence clearly establishes Tysabri as a trigger for PML through a defined mechanistic pathway, with identifiable risk factors. For Illinois patients, the statute of limitations for filing a claim is typically two years from discovery of the injury. Given the serious nature of PML and the potential for delayed diagnosis, affected individuals should consult with both medical and legal professionals promptly to evaluate their case and ensure timely action.

Important Notice

This page is for educational and informational purposes only. It does not provide medical diagnosis, treatment, or legal advice. Consult licensed clinicians and qualified attorneys for case-specific decisions.

Frequently Asked Questions

What is the statute of limitations for Tysabri-related PML claims in Illinois?

In Illinois, personal injury claims generally must be filed within two years from the date the injury was discovered or reasonably should have been discovered. For PML, this discovery date may be when symptoms first appeared or when a diagnosis was confirmed. Given the latency between Tysabri exposure and PML onset, patients should promptly seek legal counsel to assess their specific timeline.

What are the primary risk factors for developing PML while on Tysabri?

Three primary risk factors have been identified: the presence of anti-JCV antibodies, longer treatment duration (especially beyond two years), and prior use of immunosuppressants (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Patients who are anti-JCV antibody positive have a higher risk for developing PML (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).

Does submitting information create an attorney-client relationship?

No. Submission requests an initial records screening only and does not create an attorney-client relationship.

Information Registry: individuals with documented Tysabri exposure and a confirmed Progressive Multifocal Leukoencephalopathy diagnosis may request an independent eligibility review. [Begin Assessment]

References

Tysabri Prescribing Information (DailyMed)

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