Background: Magnetic resonance imaging is essential to diagnose progressive multifocal leukoencephalopathy. The broad radiological spectrum may partially be explained by genetic viral mutations and their differential neurotropism. Recent pharmacovigilance-magnetic resonance imaging studies have provided new insight into pathophysiology and radiological markers of early stages. However, how lesions evolve and why certain anatomical locations are more frequently affected remains unknown. We aim to describe a new sign - T2/fluid-attenutated inversion recovery mismatch - as a complementary marker of cavitated lesions and propose a link with the milky-way appearance, a key early sign. Furthermore, we hypothesise viral dissemination routes.
Methods: We conducted a retrospective longitudinal study from January 2010 to January 2020, to analyse clinical and magnetic resonance imaging features of 13 progressive multifocal leukoencephalopathy individuals at the symptomatic stage (mean age 58.3 years (SD ± 16.8) - 61.5% were women).
Results: The most prevalent pathology was HIV (61.5%) and motor deficit prevailed regarding other symptoms (76.9%). Frontal lobes (76.9%), middle cerebellar peduncle (61.5%), cerebellum (61.5%), and pons (53.8%) were most commonly affected, and the cortico-ponto-cerebellar pathway seemed involved in these patients. Five patients had a pure radiological pattern. Milky-way appearance was the most frequent radiological sign (58.3%). Five patients with milky-way appearance had concomitantly T2/fluid-attenuated inversion recovery mismatch (P = 0.02). This sign showed high sensitivity and specificity (100-71%, P = 0.02) to assess evolved lesions besides diffusion.
Conclusion: The possible tract-dependent spread, as well as clinical and genetic, have implications on the MRI variability of progressive multifocal leukoencephalopathy. The milky-way appearance could reflect a transitional phase towards evolved lesions, the latter demonstrated by T2/fluid-attenuated inversion recovery mismatch. Both could be key magnetic resonance imaging signs to diagnose progressive multifocal leukoencephalopathy at the symptomatic stage.
Keywords: Progressive multifocal leukoencephalopathy; magnetic resonance imaging; milky-way appearance; mismatch T2/FLAIR.