PML during dimethyl fumarate treatment of multiple sclerosis: How does lymphopenia matter? Lehmann-Horn K, Penkert H, Grein P, Leppmeier U, Teuber-Hanselmann S, Hemmer B, Berthele A Neurology. 2016 Jun 24. PMID: 27343070. Abstract CommentRecommendBookmarkWatch