Just adding that Multiple Sclerosis is an autoimmune disease (body attacking itself) for the most part. It is in the CNS (Central Nervous System) brain and spinal cord.

Guillian Barre is another one that affects the myelin. The myelin does come back. But a friend of ours was really, really bad and never came back the same. Another friend was not so bad and so came back to normal. Just depends.

Damaged myelin is also seen in syndromes such as CMT which is of the PNS (Peripheral Nervous System) which is outside the CNS. It does not involve the brain and spinal cord.

Muscular Dystrophy is in the CNS. People are born with diseased nerves. With CMT we are born with healthy nerves and it won't be prevalent unless we inherit the gene.

http://www.lindacrabtree.com/cmt/bas..._article2.html