Relapsing-remitting MS (RRMS) is characterized by clearly defined attacks of worsening neurologic function. These attacks—which are called relapses, flare-ups, or exacerbations —are followed by partial or complete recovery periods (remissions), during which no disease progression occurs.
In progressive-relapsing MS (PRMS), the disease progresses from the outset without any remissions or recovery periods — but the person also experiences occasional relapses. During these relapses, new symptoms occur or old symptoms temporarily worsen. The hallmark of PRMS is that the steady worsening of neurologic function is already underway before the person experiences any relapses. While 85% of people are diagnosed with RRMS, only 5% or so of people have PRMS.