Multiple sclerosis (abbreviated MS, also known as disseminated sclerosis or encephalomyelitis disseminata) is a chronic, inflammatory, demyelinating disease that affects the central nervous system (CNS). MS can cause a variety of symptoms, including changes in sensation, visual problems, muscle weakness, depression, difficulties with coordination and speech, severe fatigue, cognitive impairment, problems with balance, overheating, and pain. MS will cause impaired mobility and disability in more severe cases.

Multiple sclerosis affects neurons, the cells of the brain and spinal cord that carry information, create thought and perception, and allow the brain to control the body. Surrounding many of these neurons is a fatty layer known as the myelin sheath, which helps neurons carry electrical signals. MS causes gradual destruction of myelin (demyelination) and transection of neuron axons in patches throughout the brain and spinal cord. When the myelin is destroyed, the neurons can no longer effectively conduct their electrical signals. The name multiple sclerosis refers to the multiple scars (or scleroses) on the myelin sheaths. This scarring causes symptoms which vary widely depending upon which signals are interrupted.

The predominant theory today is that MS results from attacks by an individual's immune system on the nervous system and it is therefore usually categorized as an autoimmune disease. There is a minority view that MS is not an autoimmune disease, but rather a metabolically dependent neurodegenerative disease. Although much is known about how MS causes damage, its exact cause remains unknown.

Multiple sclerosis may take several different forms, with new symptoms occurring either in discrete attacks or slowly accruing over time. Between attacks, symptoms may resolve completely, but permanent neurologic problems often persist, especially as the disease advances. MS currently does not have a cure, though several treatments are available that may slow the appearance of new symptoms.

MS primarily affects adults, with an age of onset typically between 20 and 40 years, and is more common in women than in men.[1][2]