Sclerosis means scarring and refers to the lesions or plaques on nerve fibres that occur in multiple places. Early in the disease, the body can often repair the myelin (remyelination) after an attack or relapse, and the brain may also be able to adapt by creating new neural pathways (plasticity). Symptoms can therefore subside or resolve (remission) although the repaired myelin may be thinner, meaning nerve message transmission can be slower.^2,6

This relapsing remitting type of MS (RRMS) accounts for around 85 per cent of MS cases. The bulk of the remaining new diagnoses will usually be described as primary progressive MS (PPMS). In this type of MS, there is a slow continuous steady decline with no periods of remission, although symptoms may seem to stabilise at times.⁴

RRMS often progresses with the intervals between relapses becoming shorter and shorter as scarring becomes more widespread and nerves cannot be remyelinated. For two-thirds of people with RRMS, their condition then becomes secondary progressive MS (SPMS). In addition, the nerve fibres themselves become damaged increasing the degree of disability caused by the disease.^1,4,6