Why do some MS relapses last longer than others? Do some people tend to have longer relapses while others tend to have shorter ones, and if so, what factors influence this? How do steroids affect the length of individual relapses?

My relapses last four months without steroids, 4 weeks with steroids. I now have osteoporosis so want to avoid steroids. But I know patients that only have two week relapses, without steroids.