The peak onset of MS occurs between the ages of 20 and 40, involving twice as many women as men. MS is characterized pathologically by disseminated inflammatory lesions of central myelin, associated with gliosis. Clinically, MS causes symptoms and signs that vary unpredictably over decades, and may relapse, progress, or undergo spontaneous remission .
Relapses typically occur earlier in the disease course.
The relapses, although sometimes dramatic, do not always cause or increase disability. As time passes, many patients accumulate physical, emotional, and cognitive disabilities that disrupt famil y and vocational functioning. Other unfavorable signs include cognitive impairment, an insidiously progressive course, and confluent white matter lesions with brainstem-cerebellar involvement on MR imaging. Individuals who are older at onset are more likely to have a progressive course, whereas patients with predominantly sensory symptoms, optic neuritis, diplopi a, or vertigo are less likely to become disabled. Although the cause of MS remains unknown, multiple lines of evidence support an immunoregulatory disturbance triggered by a variety of infectious agents, resulting in an autoimmune disruption of central m yelin in genetically susceptible individuals.