[Epidemiology of multiple sclerosis. Controversies and realities]

Epidemiological studies of multiple sclerosis have given much information, although sometimes this is disconcerting and sometimes contradictory. The methodology used has to be improved and standardized in order to obtain studies which are comparable in different parts of the world.

Multicentric collaborating studies of similar ethnic groups under different environmental conditions may give significant key information regarding both pathogenic and trigger mechanisms. Epidemiological studies of multiple sclerosis, possibly modified by unknown environmental influences, have shown the importance of genetic susceptibility. The often quoted interrelation between prevalence and latitude still holds, although there are exceptions. Studies on incidence show that the disorder remains stable or is increasing, and most studies of prevalence show that this is increasing.