Multiple sclerosis, natalizumab, and PML: helping patients decide.

The treatment benefits of natalizumab in patients with multiple sclerosis (MS) appear to exceed those of other disease-modifying drugs, but progressive multifocal leukoencephalopathy (PML) has been identified as a risk in patients receiving natalizumab. As of August 2011, a total of 150 cases of natalizumab-associated PML had been reported worldwide. The overall risk is estimated at approximately 1.66 in 1,000 patients. Independent risk factors for natalizumab-associated PML are number of infusions beyond 36 and prior use of immunosuppressive drugs. Classifying JC virus antibody status appears to be useful in treatment decision-making for individual MS patients. Patient tolerance for risk plays an important role in the selection of therapy, and the treating physician's perception and tolerance of risk may differ markedly from the patient's. Physicians can help patients make individual informed decisions regarding the use of natalizumab, given the known risk of PML.