Multiple sclerosis (MS) is at onset an immune-mediated demyelinating disease. That means the nerve fiber covering - imagine a power cable with no covering around the wire. You couldn't control the path of the electricity. That means you cant make it work how you want, like play your stereo. So in comparison, my covering around my electric nerve is missing in places and I cant always make it work the way I want, Like feel that that stove is HOT. In most cases, it starts as a relapsing-remitting disease with distinct attacks and no symptoms between flares. Over years or decades (some unfortunately from the get go), virtually all cases transition into a progressive disease in which insidious and slow neurological deterioration occurs with or without acute flares. Relapsing-remitting disease is often responsive to immune suppressive or modulating therapies (Like Avonex, Betaseron, Copaxone and Rebif), while immune based therapies are generally ineffective in patients with a progressive clinical course. Disability correlates better with measures of axonal atrophy than immune mediated demyelination. Therefore, immune based therapies, in order to be effective, need to be started early in the disease course while MS is predominately an immune-mediated and inflammatory disease. While current immune based therapies delay disability, no intervention has been proven to prevent progressive disability.
Here is the National Multiple Sclerosis Society webpage if you would like to do further reading
