Cramer SP, et al. - Researchers ascertained if blood–brain barrier (BBB) permeability, as measured by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), can provide early detection of suboptimal treatment response in relapsing–remitting multiple sclerosis (RRMS). For this investigation, 35 RRMS patients beginning on fingolimod or natalizumab, drugs with a common effect of decreasing lymphocyte influx into the central nervous system, were scanned with DCE-MRI at 3T prior to treatment and at 3 and 6 months posttreatment. They reported that BBB permeability as measured by DCE-MRI reliably predicts suboptimal treatment response and was a surrogate marker of the state of health of the BBB. A predictive threshold for disease activity was found, which was remarkably identical in clinically isolated syndrome and established RRMS as investigated here.