The distribution of magnetic resonance imaging response to interferonβ-1b in multiple sclerosis

Whereas the effect of interferons (IFNs) on magnetic resonance imaging (MRI) outcome measures in patients with multiple sclerosis (MS) has been convincingly shown, little work has been done to define the between-patient heterogeneity of treatment response. Our aim was to assess the distribution of the effect of IFN beta-1b in terms of reduction of active T2 lesions in patients with MS. Using a fixed and a random effects model, we investigated the distribution of active T2 lesions reduction over a three-year follow up in response to treatment with 250mcg IFN beta-1b every other day in 695 patients with a complete MRI data-set of the 718 (97%) enrolled in the European, multicenter, randomised, double-blind, placebo-controlled trial of secondary progressive MS. The two statistical models consistently showed that the between patient response to IFN beta-1b, in terms of reduction of active T2 lesions, is highly heterogeneous. Whereas treated patients have a high probability (more than 65%) of showing an active T2 lesion reduction equal to or greater than 60%, there is also a 7% probability for treated patients not to show any reduction of MRI-detected disease activity during the course of the trial or even to have an increase of T2 active lesions. This study might be regarded as a first step toward the definition of markers potentially useful to identify IFN beta treatment responders and non-responders with regard to T2 lesion activity.