Journal of NeuroVirology

, Volume 22, Issue 4, pp 533–535 | Cite as

Reassessing the risk of natalizumab-associated PML

  • Joseph R. BergerEmail author
  • Robert J. Fox
Short Communication


The risk algorithm for natalizumab-associated PML was first established in 2012 using the observations that JC virus antibody status, prolonged duration of natalizumab therapy (>2 years), and prior exposure to immunosuppressive therapy increased the risk for the disease. Prior to the publication of Biogen’s algorithm, a risk algorithm was created by Fox and Rudick using an Excel spreadsheet in order to address the concerns of their patients. Applying the most recently available data regarding natalizumab-associated PML, the risk assessments for PML were recalculated. The current numbers indicate substantially higher risks for PML in 2015 than in 2012. Our calculations suggest that an individual having all three risk factors has an approximately 1 in 44 chance of developing PML.


Natalizumab Progressive multifocal leukoencephalopathy (PML) Multiple sclerosis Disease modifying therapy 


Author contributions

Drs. Berger and Fox were equally responsible for study concept and design, data acquisition, analysis and interpretation of the data, and critical revisions.

Compliance with ethical standards

Conflict of interest

Joseph R. Berger, M.D.: Receives personal consulting fees from Biogen, Bristol Myers Squibb,, EMD Serono, Forward Pharma, Genzyme, Genentech, Inhibikase, Incyte, Janssen, Johnson and Johnson, Novartis; serves on PML Adjudications Committees for Amgen, Astra-Zeneca, Eisai, Milennium/Takeda, Pfizer, and Roche/Genentech; receives research grant support from Biogen; and serves as an assistant editor of the Journal of Neurovirology.

Robert J. Fox, M.D.: Receives personal consulting fees from Actelion, Biogen, Genentech, Mallinckrodt, MedDay, Novartis, Teva, and XenoPort; serves on advisory committees for Biogen Idec and Novartis; received research grant funding from Novartis; receives royalties for editing Multiple Sclerosis and Related Disorders; and serves on the editorial boards for Neurology and Multiple Sclerosis Journal.

Funding sources



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Copyright information

© Journal of NeuroVirology, Inc. 2016

Authors and Affiliations

  1. 1.Multiple Sclerosis Division of the Department of NeurologyUniversity of PennsylvaniaPhiladelphiaUSA
  2. 2.Mellen Center for Multiple Sclerosis Treatment and Research, Neurological Institute, Cleveland ClinicClevelandUSA

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