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. 2012 Nov;8(11 Suppl 8):1–20.

Table 1.

Risk Factors for the Development of Progressive Multifocal Leukoencephalopathy (PML) in Patients Treated with Natalizumab

Risk factor Impact on PML risk
Longer duration of natalizumab treatment Incidence of PML according to duration of natalizumab exposure:

  • 1-11 months: 0.04 cases per 1,000 patients (95% CI, 0.01-0.11)

  • 13-24 months: 0.56 cases per 1,000 patients (95% CI, 0.39-0.78)

  • 25-36 months: 1.99 cases per 1,000 patients (95% CI, 1.59-2.45)
Prior immunosuppressant treatment Immunosuppressants associated with PML include mitoxantrone, cyclophosphamide, methotrexate, azathioprine, and mycophenolate.
Presence of anti-JCV antibodies Estimated incidence of PML according to anti-JCV antibody status:

  • Negative for anti-JCV antibodies: 0.11 cases per 1,000 patients (95% CI, 0-0.59)

  • Positive for anti-JCV antibodies: 2.16 cases per 1,000 patients (95% CI, 1.40-3.18)

CI=confidence interval; JCV=JC virus.

Data from Sørensen PS, et al.6