Multiple sclerosis (MS) is a chronic disease characterized by inflammation, demyelination, gliosis (scarring), and neuronal loss;(1)
The term MS refers to two characteristics of the disease :
the numerous affected areas of the brain and spinal cord producing multiple neurologic symptoms that accrue over time, and the characteristic plaques or sclerosed areas that are the hallmark of the disease (2)
The disease has a mean age at onset of 30 years. Because of the young age at onset,MS has a dramatic effect on employment and, in fact, is the most common cause of disability in young adults. Overall life expectancy is decreased by about 10 years compared with age-and sex-matched control subjects.(3)
Pathogenesis : Many aspects of the pathophysiology of MS remain unclear(3) Foremost in unresolved issues is the identity of the actual initiating factor for the autoimmune and inflammatory processes that characterize MS. Through the years, several dozen triggers have been proposed. Current thinking is that a genetically susceptible individual contracts an unidentified viral or bacterial infection that initiates the autoimmune cascade.. The triggering infectious agent likely has proteins the mimic myelin proteins, so that the body mounts an immune response to its own myelin.
There are two pathological processes that occur during MS. The first is inflammatory. During this process, the body mounts an autoimmune attrack on the myelin covering of nerve fibers of the white matter in the CNS. These areas of demyelination are visualized as plaques or lesions and are seen on brain tissue directly(e.g., on autopsy) or on MRI with contrast agents . It is this inflammation that causes the relapses that are seen clinically,and it is the resolution of these relapses that is seen as remission.
The second process is neurodegenerative, during which the axons of nerves in brain white matter are demaged, some irrevocably.This neurodegeneration causes a progressive disability when transmission through the nerve cell is slowed or fails completely.It is cumulative with time and may be irreversible.(3)
role played by these various mechanisms in vivo remains
to be established