Figure 3. Risk factors, triggers, modifiers, and disease courses.

It is exceedingly unlikely that multiple sclerosis will ultimately be attributed to a single cause. Rather, the genetic and environmental factor or combination of factors that predispose to and initiate the disease, and that modify its course, are highly diverse from one person to the next. The top row of the figure depicts the funneling of proposed factors, for which varying levels of evidence exist, into the development of inflammatory, demyelinating lesions with heterogeneous axonal loss (second row). The third row lists features of the lesions and their consequences that are generally salutary or deleterious and that modify the chance of progression (bottom row).