What are the risk factors for developing progressive multifocal leukoencephalopathy (PML) in patients with Crohn disease?

Updated: Jul 26, 2019
  • Author: Leyla J Ghazi, MD; Chief Editor: Praveen K Roy, MD, AGAF  more...
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PML is an opportunistic infection caused by the JC virus that typically only occurs in patients who are immunocompromised. As of August 1, 2012, there were 271 confirmed cases of PML worldwide; in individuals treated with natalizumab, one was a patient with Crohn disease who was receiving 35 infusions of natalizumab. [108] Individuals at risk include those with the following [109] :

  • JC virus antibody positivity

  • Previous exposure to immunosuppressant therapy

  • More than 2 years of treatment with natalizumab

The risk of developing PML is less than 1 in 1000 users, but it increases to 11 per 1000 users if all 3 risk factors are present. [109]

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