Interesting question, John. I don't have MS, I've got MG. (I followed you over here from the link you left on the gluten sensitivity forum)
I don't know if you would expect the same left side effect with MG or not, but my left arm is usually more fatigued than my right. However, my right leg is more fatigued than my left. Of course, that may be because my right leg is my short leg, so it has always taken more abuse than the other over the years.
I'll follow this thread with interest to see what replies you get.