Conventional and diffusion-weighted MRI in progressive multifocal leukoencephalopathy: new elements for identification and follow-up.

Progressive multifocal leukoencephalopathy (PML) is a serious disorder that primarily affects individuals with a suppressed immune system. Few semiological elements help clearly distinguish PML from other diseases included in the differential diagnosis. Moreover, the clinical course of disease may be chronic or rapidly progressive, with different magnetic resonance imaging (MRI) patterns. The purpose of this study was to confirm the diagnostic value of conventional MRI sequences combined with diffusion-weighted imaging (DWI) in PML to identify those patients with worst prognosis. We used both conventional MRI sequences and DWI to monitor four male patients aged between 40 and 50 years affected by PML. In two patients, the disease rapidly led to death whereas the other two patients presented a chronic course. Conventional MRI sequences enable detection of the extension of white matter lesions. DWI permits more accurate differentiation of the disease progression front, which exhibits low signal intensity in apparent diffusion coefficient (ADC) maps, from the central gliotic area of demyelinisation, characterised by high ADC values. Patients with rapidly evolving PML have a clear progression front on DWI, which seems to be very tenuous, if not absent, during the quiescent phases of the disease. The addition of DWI sequences to conventional MRI seems to be a valid method for accurately diagnosing PML and establishing the degree of disease progression. [ABSTRACT FROM AUTHOR]