Randomized, double-blind, placebo-controlled study of subcutaneous interferon beta-1a in relapsing-remitting multiple sclerosis: a categorical disability trend analysis

The treatment effects of recent immunomodulatory therapies on disease progression in relapsing-remitting multiple sclerosis (MS) have been mostly established from ‘confirmed progression’ endpoints. However, the reliability of this outcome measure is poor and a significant proportion of patients may be erroneously classified. We previously proposed the area under disability/time curves to quantify in-trial disability changes, but although these have advantages, they lack information on the direction of change. We have therefore performed disease trend analyses and categorical classifications using serial Expanded Disability Status Scale (EDSS) scores from the 533 complete datasets in a double-blind, randomized, placebo-controlled, phase III trial of subcutaneous interferon β-1a (IFNβ-1a) (PRISMS study). We found significant treatment benefits for IFNβ-1a on in-trial disability course (P=0.002). Therapeutic advantages remained when relapse-related assessments were excluded (P=0.018). Post hoc analyses demonstrated that IFNβ-1a was mainly effective in both increasing the proportion of patients with a ‘stable’ course and reducing those with prolonged, disabling deteriorations. Baseline disease duration and EDSS levels, but not MRI lesion load, predicted the subsequent disability trends. Mean ‘numbers needed to treat’ (NNTs) to obtain preferred disability courses were reduced in patients with shorter disease duration. These results have important implications for the targeting of immunomodulatory therapies in MS.