Relapsing Remitting MS (RRMS) describes a course of MS characterized by unpredictable but clearly defined episodes during which new symptoms appear, or existing ones get worse. These ‘episodes’ are also known as attacks, exacerbations, or flare-ups. Typically attacks come on over a few hours to a few days, and last anywhere from at least 48 hours to a few months. The hallmark of RRMS is the recovery, or ‘remission’ that occurs between attacks. In the period between attacks, recovery is complete (figure 1a), or nearly complete (figure 1b) to pre-attack function, and this recovery persists for a clear period of time. The time between attacks is variable but can be months or even years. About 85% of people have RRMS at the time of diagnosis.
There are two subgroups sometimes referred to in RRMS:
Benign MS in which remission between relapses is almost complete such that 15 – 20 years after diagnosis, there is little if any accumulation of physical disability. In most cases of benign MS, symptoms mainly affect the senses of sight and/or touch. The proportion of people considered to have benign MS decreases over time and recent research suggests that when cognitive function is examined, that the incidence of truly benign disease may be lower than originally thought. The challenge for treatment is that benign disease cannot be predicted at outset and so disease modifying treatment remains an important consideration.
Clinically Isolated syndrome (CIS) refers to a single episode of neurological symptoms. This is also sometimes referred to as probable MS. Often, on investigation using MRI and/or evoked potentials, the doctor finds laboratory evidence of a second attack which then defines RRMS. In very early MS, it may be necessary to follow things and repeat investigations a few months later to find evidence of a second defining MS attack.
Primary Progressive MS (PPMS)describes a course of MS which is characterized by a slow accumulation of disability, without relapses (figure 2a). It may stabilize for periods of time, and even offer minor temporary improvement (figure 2b), but overall, there are not periods of remission in PPMS. Approximately 10% of people diagnosed with MS have PPMS and it is the only form of MS to affect men and women equally. PPMS tends to be diagnosed after age 40.
Secondary Progressive MS (SPMS) follows on a course of RRMS. Over time, distinct relapses and remissions become less apparent and the disease begins to worsen steadily (figure 3a). Occasional flare-ups, minor improvements, and even periods of stability may occur, but overall, the picture is one of accumulating disability (figure 3b). About 50% of people with RRMS will develop SPMS within 10 years of diagnosis. There is not yet reliable long term data available on the impact of disease modifying therapy and conversion to SPMS.
Progressive Relapsing MS (PRMS) is the rarest course of MS, occurring in only about 5% of people diagnosed. People with this form of MS experience steadily worsening disease from the beginning, but also experience clear attacks of symptoms, with (figure 4a) or without recovery (figure 4b). They do not experience remissions in the sense that patients with RRMS do. Sometimes patients with this form of MS are originally diagnosed with PPMS, then experience an acute attack, establishing the diagnosis of PRMS.