Background: Progressive multifocal leukoencephalopathy (PML), a destructive demyelinating infection which lytically infects oligodendrocytes, has occurred in patients treated with natalizumab. Magnetic resonance imaging (MRI) scan imaging of the brain gives clues to diagnosis but is nonspecific in distinguishing multiple sclerosis from PML. Spinal fluid detection of JC virus is specific but incompletely sensitive. Associated immunosuppression is typically of the cell-mediated type but can be poorly defined on clinical grounds.
Review summary: It is apparent that natalizumab is a predisposing factor for developing PML from the 3 cases of natalizumab-treated patients. There is no reliable presymptomatic way to detect PML or JC virus infection of the brain by virologic or imaging surveillance techniques. One patient with multiple sclerosis and natalizumab treatment has survived, indicating that withdrawal of antibody, possibly in combination with antiviral therapy, may permit survival. However, immune reconstitution disease is a risk after immune restoration and withdrawal of natalizumab. PML deficits would be expected to be permanent. The estimate of incidence of PML in natalizumab-treated patients is 1 per 1000. The duration of natalizumab treatment may be an independent risk factor for development of PML.
Conclusion: PML, a usually fatal neurologic infection, should be considered as a risk factor when using natalizumab. The treatment of multiple sclerosis patients with natalizumab is a matter of informed risk, individualized for each multiple sclerosis patient.