Multiple Sclerosis Definition: Multiple sclerosis is a demyelinating disease causing widespread degeneration of the central nervous system (CNS) which progressively leads to serious neurological deficits. The disease is characterized by remissions and relapses, irregular onset, and acute flare duration. Each relapse may involve different areas of the white matter of the central nervous system (CNS). Etiology: It may be a genetic and environmental factor that may cause an immunologically mediated inflammatory response with the CNS. The immune response in mediating tissue damage and the extent to which these changes are the cause or consequence of myelin damage remains overly established. Exposure to other viral illnesses such as measles, mumps, and rubella quite late in childhood may be a factor in people at risk of developing the illness. Additional evidence for genetic susceptibility is provided by epidemiological studies within and between ethnicities. The risk is to raise a group for the offspring and for the brothers and sisters of those affected. Apart from this, the environment can be relatively more protective. Age is also a factor in immigrant populations. Dean (1967) stated that multiple sclerosis is higher in people who emigrated as adults rather than children. Additionally, multiple sclerosis does not have a single cause. A new episode of demyelination is more likely to occur following viral infection but no single agent is involved. Pathology: Demyelination is a disintegration of the myelin sheath caused by an inflammatory and destructive process, the axon being partially or completely denuded. The hallmarks of multiple sclerosis lesions are perivascular inflammation followed by myelin depletion, oligodendrocyte loss, and astroglial proliferation. Initial stage characterized by the accumulation of inflammatory cells, lymphocytes and monocytes around the Venules of the CNS. Inflammation can cause a functional block of conduction through myelinated axons. Then, there is an active destruction of the oligodendrocytes and its myelin sheath following contact with macrophages and microglia. This was followed by depletion of oligodendrocytes in which denuded axons were observed in the lesion. Finally, the lesion heals through scar formation dependent on astrocytic reactivity, producing hardened plaques or plaques from which the disease derives its name. the most common sides of the plaques are in the border of the gray matter of the cerebellum, cerebellar white matter, optic nerves, cervical part of the spinal cord and brainstem. Diagnostic Criteria for Multiple Sclerosis Many different diagnostic criteria have been proposed over the year. The criterion that colleagues formulated in 1965 defined relapses worsening symptoms lasting more than 24 hours and spaced one month apart. It is still used today in practice and in research protocols..