The general "rule of thumb" is that...

MS is a two-stage disease, with initial attacks of inflammatory demyelination, which damages myelin, followed approximately 10 years later by a slow, progressive neurdegenerative phase marked by loss of axons and nerve cells.

http://home.ix.netcom.com/~jdalton/ms-two-stages.pdf

http://home.ix.netcom.com/~jdalton/two%20stage%20MS.jpg

jackD

p.s. It is hoped that intervention with drugs CRAB might delay or prevent this.