Multiple sclerosis (MS) is a is a chronic inflammatory disease resulting in progressive demyelination and axonal loss within the central nervous system, leading to numerous physical and mental symptoms, which follow different patterns of evolution and variable rates of disability accumulation. The symptoms include changes in sensation (reduced sensitivity and numbness), muscle weakness, muscle spasms, or difficulty in moving, difficulties with coordination and balance, problems in speech or swallowing, visual problems, fatigue and pain (both acute and chronic); along with bladder and bowel difficulties. Other features include cognitive impairment of varying extent, as well as depression. All of these symptoms can be transient but, as the disease progresses, they become increasingly permanent.
The different courses of MS. Relapsing-remitting MS (RR-MS) is the most common form of MS and is characterised by clearly defined disease relapses with full recovery or with some after affects upon recovery. In primary progressive MS, there is a gradual and nearly continuous worsening of symptoms with minor fluctuations, but no distinct replaces. Secondary progressive MS (SP-MS) is characterised by an initial relapsing-remitting disease coursed followed by progression with or without occasional relapses, minor remissions and plateaus. SP-MS is probably the inevitable consequence of RR-MS. Progressive-relapsing MS is defined as progressive disease from onset, with or without recovery, associated with periods between relapses characterised by worsening progression; it is very similar to SP-MS.
The global incidence and prevalence of MS is estimated to be 2.5 and 30 per 100,000 individuals, respectively According to the US National MS Society, there are approximately 2.5 million individuals with MS worldwide. This, coupled with the fact that the disease most commonly manifests in individuals in their late twenties, means that the magnitude of the disease burden, measured in terms of the number of working days lost, is high.