If you or a loved one is taking Tysabri, you may have heard about the risk of progressive multifocal leukoencephalopathy (PML). This rare but serious brain infection has been closely studied, and certain patient groups require more vigilant monitoring. Building on decades of pharmacovigilance research, this page explains the risk factors and what the latest adverse event reports reveal about who may need closer observation.
Tysabri (natalizumab) is a biologic therapy approved for the treatment of multiple sclerosis and Crohn's disease. Its use is associated with a significantly increased risk of progressive multifocal leukoencephalopathy (PML), a severe opportunistic brain infection caused by the JC virus. The long-term prognosis for patients who develop PML after Tysabri exposure is poor, with the condition usually leading to death or severe disability (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). PML is an opportunistic viral infection of the brain that typically only occurs in immunocompromised individuals. In Tysabri-treated patients, the infection results from reactivation of the JC virus, which is normally kept in check by the immune system. The clinical presentation of PML can be variable, often including progressive neurological deficits such as weakness, cognitive decline, visual disturbances, and coordination problems. Diagnosis is typically confirmed by brain MRI showing characteristic white matter lesions and detection of JC virus DNA in cerebrospinal fluid. Because PML symptoms can mimic multiple sclerosis relapses, careful monitoring is essential (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).
Three well-established risk factors increase the likelihood of developing PML in Tysabri-treated patients: the presence of anti-JCV antibodies, longer treatment duration (especially beyond two years), and prior use of immunosuppressants. Patients who are anti-JCV antibody positive have a higher risk for developing PML. These factors should be considered in the context of expected benefit when initiating and continuing treatment with Tysabri (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). The mechanistic pathway linking Tysabri to PML involves the drug's mode of action. Tysabri is a monoclonal antibody that binds to alpha-4 integrin, preventing immune cells from crossing the blood-brain barrier. This reduces inflammation in the central nervous system, which is beneficial for treating multiple sclerosis and Crohn's disease, but it also impairs immune surveillance against JC virus in the brain. This loss of immune control allows the virus to replicate and cause PML.
Regarding the timeline between exposure and documented harm, PML has been reported during Tysabri treatment and also following discontinuation. In clinical trials, PML occurred in three patients: two cases were observed in the 1869 patients with multiple sclerosis who were treated for a median of 120 weeks, and the third case occurred after eight doses in one of the 1043 patients with Crohn's disease who were evaluated for PML (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Importantly, PML has been reported following discontinuation of Tysabri in patients who did not have findings suggestive of PML at the time of discontinuation. Therefore, patients should continue to be monitored for any new signs or symptoms that may be suggestive of PML for at least six months following discontinuation of Tysabri (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).
The adequacy of warnings regarding Tysabri and PML is reflected in the product labeling. The prescribing information includes a boxed warning that states Tysabri increases the risk of PML, an opportunistic viral infection of the brain that usually leads to death or severe disability. The warning emphasizes that healthcare professionals should monitor patients for any new sign or symptom suggestive of PML and that Tysabri dosing should be withheld immediately at the first sign or symptom suggestive of PML (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Because of the risk of PML, Tysabri is available only through a restricted distribution program called the TOUCH Prescribing Program (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). Prognosis-related considerations for affected patients are grave. PML usually leads to death or severe disability. The outcome depends on factors such as the extent of brain involvement, the patient's immune status, and how quickly Tysabri is discontinued. Early detection and withdrawal of Tysabri may improve prognosis, but many patients still suffer significant neurological impairment. In multiple sclerosis patients, an MRI scan should be obtained prior to initiating therapy with Tysabri to help differentiate subsequent multiple sclerosis symptoms from PML. In Crohn's disease patients, a baseline brain MRI may also be helpful (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962). In summary, the long-term outcome of PML after Tysabri is poor, with high rates of death or severe disability. The risk is increased by anti-JCV antibodies, longer treatment duration, and prior immunosuppressant use. Adequate warnings are provided through boxed labeling and the restricted distribution program, but the prognosis remains serious. Monitoring for symptoms during and for at least six months after treatment is critical.
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.
The long-term prognosis for PML after Tysabri is poor, with the condition usually leading to death or severe disability. Early detection and discontinuation of Tysabri may improve outcomes, but many patients still suffer significant neurological impairment (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).
Three well-established risk factors increase the likelihood of developing PML: 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).
Yes, PML has been reported following discontinuation of Tysabri in patients who did not have findings suggestive of PML at the time of discontinuation. Monitoring for symptoms should continue for at least six months after stopping Tysabri (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c5fdde91-1989-4dd2-9129-4f3323ea2962).
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