In this report we describe a multiple sclerosis patient who developed a relapse with magnetic resonance imaging (MRI) features of tumefactive demyelination after switching therapy from natalizumab to fingolimod. Tumefactive lesions emerged 16 weeks after stopping natalizumab and eight weeks after commencing fingolimod therapy but had been absent at the time of diagnosis and throughout the preceding course of the disease. Thus, the first-time occurrence of atypical lesion features may have been caused by the change in immunotherapy. The possible relevance of natalizumab withdrawal vs fingolimod introduction is discussed against the background of recently published case studies.
