This is why M.S. is classified as a neurological disease and is the speciality of neurologists. This type starts with a small number of mild attacks followed by complete recovery. This means they have attacks followed by remissions. From the start they experience steadily worsening symptoms and progressive disability. The central thing that is happening in M.S. is myelin is breaking down.
Myelin is like a coating around nerve fibres.
In M.S. the myelin in the central nervous system suffers patches of demyelination. Therefore messages from your brain can't get to your limbs. Whatever the reasons for this breakdown, myelin can regenerate.