Progressive Multifocal Leukoencephalopathy Syndrome and Immune Reconstitution Inflammatory Syndrome

Progressive multifocal leukoencephalopathy (PML), an opportunistic viral infection of the central nervous system caused by the JC virus, typically manifests in severely immunocompromised conditions, ranging from HIV/AIDS to lymphoproliferative malignancies to the consequence of immunosuppressant medications such as natalizumab, a monoclonal antibody approved for the treatment of relapsing forms of MS. In this chapter, we discuss the typical symptomatology and radiographic findings of PML and how to distinguish it from those of MS. In addition, we review the management of PML in natalizumab-treated MS patients as well as the features of immune reconstitution inflammatory syndrome (IRIS), the potentially life-threatening consequence of natalizumab withdrawal in patients with PML.