MS is not different from other autoimmune inflammatory diseases such as arthritis and lupus, which may affect joints and other tissues, and even bronchial asthma which inflames bronchial tubes. These autoimmune conditions only differ in which tissue is inflamed. We know very little about what incites inflammation. Inflammation in the nervous system destroys myelin and the oligodendrocytes. After tissue destruction a scar or hardening forms, the MS plaque.
Plaques are similar to scars forming on skin after an injury.
The tissue is repaired but is not exactly like it was before. Much of the myelin doesn't get replaced. The general area may appear harder or tougher. This is where the disease gets its name, multiple sclerosis or multiple scarring. Ordinarily the size of the plaques is quite small, only a fraction of an inch in diameter, but it may form in a very strategic place to block signal transmission.