Purpose of review: This review describe the role and advancements of MRI in the diagnosis and monitoring of progressive multifocal leukoencephalopathy (PML) in multiple sclerosis patients treated with natalizumab.
Recent findings: MRI is the most sensitive paraclinical tool in the detection of PML lesions in natalizumab-treated multiple sclerosis patients, showing lesions in very early disease stages up to months before clinical symptoms occur. The sensitivity of PML lesion detection is dependent on the MRI pulse-sequences used. Fluid-attenuated inversion recovery shows the highest sensitivity and diffusion-weighted MRI is well suited to depict active and acute demyelination in PML lesions. Compared with the PML in HIV-infected patients, the MRI appearance of natalizumab-associated PML is rather heterogeneous and fluctuating, including signs of inflammation and showing new imaging patterns such as cortical grey matter involvement. The importance of reliable PML detection is particularly obvious in patients at an asymptomatic stage. The clinical relevance of natalizumab-associated PML detected at an asymptomatic stage is best illustrated by the fact that such patients have a substantially better outcome compared with symptomatic PML patients.
Summary: MRI is the most powerful method in the detection of natalizumab-associated PML by showing imaging patterns helpful in the differentiation between PML and multiple sclerosis lesions. The early - preferably asymptomatic - detection of PML is related to a more favorable outcome in terms of survival and functional outcome parameters.