Most people I know that have MS actually gain weight because they aren't able to move like they used to. There are diseases that cause weight loss, diabetes, lupus, and a host of others. I hope your doc thoroughly addresses this.
I imagine if you have been depressed or just too fatigued to eat that it could cause weightloss and if you have stopped excercising or being up and about, it would cause muscle loss but not MS specifically. Let us know what you find out.
"Life shouldn't be a journey to the grave with the intention of arriving
safely in a pretty and well preserved body, but rather, to skid in
broadside, thoroughly used up, totally worn out, and loudly
shouting...."Wow! What a ride! Thank You Lord!!!"