Smoking and M.S

I saw my neurologist about 4 weeks ago and he said there is a chance I have M.S (or something else - I didn't catch the name).  I have 4 marks on my brain which are white matter ( he showed me on the screen and they look quite large) I don't understand what this white matter is and would love to know more about M.S  He never said I actually DO have M.S but he told me I HAVE TO give up smoking.  Does anyone know why smoking would affect M.S (apart from the fact that smoking causes many medical problems).  I am 55 years old and have smoked for approx 40 years and it would be pure hell for me to give up smoking.  My Mother used to be a nurse and she always loathed smoking.  However, she reckoned that if I stopped smoking I would die of stress.  I'm truly serious about this and not looking for an "easy way out"  My biggest problem in this fact that I know I don't want to give up smoking.   Could someone please help me  learn about M.S. and what the symptoms are (or can be)  and anything else they think may cause these problems (i.e. another disease)  Many thanks