MS begins as a disease of intermittent episodes with recovery in between. With time, however, MS changes to a progressive disease with increasing disability.  In her talk, Dr. Stadelmann explains that studies of MS brain lesions have identified specific changes that occur with disease progression. For example, chronic MS lesions contain many fewer oligodendrocytes than do early lesions.  Since oligodendrocytes produce the myelin sheath that surrounds axons, drugs that stimulate the migration and establishment of oligodendrocytes in lesions may increase axonal remyelination and improve the prognosis of MS patients. Stadelmann also explains that brain lesions can be caused by conditions other than MS, such as neuromyelitis optica.  Improved studies will help to correctly diagnose and treat these distinct diseases.