Methods: In this retrospective review, the first 40 natalizumab-treated MS patients diagnosed with PML in the postmarketing setting were identified, of whom 22 (10 with clinically diagnosed immune reconstitution inflammatory syndrome) fulfilled the inclusion criteria for this study. Magnetic resonance images were analyzed according to predefined criteria by 5 independent readers.
Results: The most frequent lesion pattern in early scans from PML patients was that of large (>3 cm, 15/18), subcortical (18/18), T2 or fluid attenuated inversion recovery (FLAIR) hyperintense (18/18), T1 hypointense (17/18), and diffusion hyperintense (15/15) lesions, with a sharp border towards the gray matter and an ill-defined border towards the white matter (18/18) on T2-weighted images. We could detect contrast enhancement in 41% (7/17) of the cases on the first scan at clinical presentation.
Interpretation: Attention to characteristic MRI patterns, especially the presence of contrast enhancement, and the subcortical location may have utility in screening and early diagnosis of PML in natalizumab-treated MS patients.
It is is important that we can recognize the development of PML as early as possible, however we urgently need something to combat the virus such that such early detection can have a positive outcome.