Accumulation of disability in typical relapsing MS: Pooled analysis of the OPERA I and II trials


  • Steady progression independent of relapse activity (PIRA), rather than relapse-associated worsening (RAW), was the main contributor driving disability accumulation in typical patients with relapsing multiple sclerosis (MS). This data challenges the current clinical dichotomy of distinct relapsing versus progressive forms of MS.

Why this matters

  • Disability accumulation in people with MS can occur stepwise following discrete relapses, known as “disability worsening” (or RAW), and/or via a continuous, steady progression independent from relapses, known as “disability progression” (or PIRA).

  • Relapsing MS and secondary progressive MS both may involve stepwise RAW; primary progressive MS, characterized by an absence of discrete relapse events, will have disability accumulation via PIRA.

  • However, evidence suggests that people with relapsing MS commonly worsen over time despite well-controlled relapse activity.