Multiple sclerosis is a demyelinating disease. What is myelin? Myelin is the layer of Chevron cells that surrounds the surface of the axon of a nerve cell. To use an analogy, the axon of a nerve cell is like a metal wire that transmits signals, and the myelin sheath is a plastic skin wrapped around the surface of the wire to ensure that the electrical signals are transmitted accurately and quickly. Demyelinating disease, or loss of myelin, obviously affects the signaling of nerve cells innervating muscles or sensory organs, resulting in abnormal movement or sensation. There are many causes of demyelination. In addition to the most common arteriosclerotic subcortical leukoencephalopathy associated with chronic cerebral ischemia in the elderly, autoimmune diseases, and nutritional deficiencies can all lead to demyelination. Among the autoimmune diseases of the central nervous system in young adults, multiple sclerosis and optic neuromyelitis optica are more common, and sometimes when the patient’s condition does not fully meet the diagnostic criteria for multiple sclerosis, or when the diagnosis is not fully confirmed, it is often referred to as demyelinating disease in general. There are similarities in the treatment of autoimmune demyelinating disorders of the central nervous system.