MRI and clinical activity in MS patients after terminating treatment with interferon beta-1b

Monthly MRI activity and clinical disability were evaluated in two relapsin g-remitting multiple sclerosis (RRMS) patients for 4 years during a crossov er treatment trial with IFN beta-1b and for a mean of 21 months after termi nating treatment with IFN beta-1b Post-treatment MRI activity was compared to baseline activity in these patients. Although contrast enhancing lesions (CEL) and the bulk white matter lesion load (BWMLL) on T2-weighted images eventually returned to baseline values, there was a refractory period of 6- 10 months after terminating treatment, before baseline MRI activity was res tored. Although the mechanism for a sustained effect of IFN beta-1b is uncl ear at this time, these results have important implications for enrollment of such patients into new treatment protocols that rely on contrast enhanci ng lesion frequency as on outcome measure.