The NICE guidelines actually say patients are supposed to be told at diagnosis there is NOTHING they did to cause it, as it’s not a “lifestyle” disease.
Unfortunately, too few consultants seem to bother with this, which could end a lot of fruitless soul searching about: “Why me?”, and “What have I done?”
Smoking is one of the very few lifestyle choices known to be a risk factor. However, I have never yet seen anyone go so far as to suggest it was a cause, let alone THE cause. A risk factor is very far from being a cause. Millions of people smoke, who never get MS, and thousands of people get MS, who have never smoked.
So IF you have other risk factors (mostly genetic) smoking might just be one thing that tilts the odds slightly more in favour of getting it - but it’s not a cause in itself, and I certainly can’t see how stopping could ever be.
I do wonder, though, if there’s any chance the nicotine buzz could have masked symptoms that, in fact, would have become apparent earlier. I’ve no scientific evidence to back this up, I just wonder if quitting smoking may have made any underlying health issues more noticeable. Other than that, just complete coincidence. As both Alison and Whammel say, far from smoking being protective against MS, it’s known to be a risk factor (although a 50% increase in a very small risk is still a very small risk…)