Compared with multiple sclerosis (MS), progressive multifocal leukoencephalopathy (PML) is more likely to produce large, confluent lesions on T2-weighted magnetic resonance imaging (shown). Clinically, PML more often presents with hemiparesis and mental status changes, whereas MS is more likely to produce optic neuritis, brainstem syndromes, and spinal cord lesions. However, it is often impossible to distinguish a relapse of MS from PML based solely on clinical and ­radiologic findings, and a lumbar puncture with PCR for JC virus is usually required for definitive diagnosis. (Reproduced, with permission, from Ropper AH, Samuels MA. Adam’s & Victor’s Principles of Neurology, 9th ed. New York, NY: McGraw-Hill; 2009. Fig. 33-4B.) Source: Multiple Sclerosis, Principles and Practice of Hospital Medicine, 2e Citation: McKean SC, Ross JJ, Dressler DD, Scheurer DB. Principles and Practice of Hospital Medicine, 2e; 2017 Available at: http://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/Books/1872/mckeanhm2_ch212_f002.png&sec=146987057&BookID=1872&ChapterSecID=146987023&imagename= Accessed: December 22, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved