Neuroepidemiology has undoubtedly played a fundamental role in the study of
multiple sclerosis (MS) by providing some aetiologic clues, although a def
initive basis for the conclusive resolution of its enigma is still lacking.
Epidemiological and genetic studies have indicated that MS is probably cau
sed by multiple factors, both genetic and environmental, none of which is i
ndividually sufficient, which appear to act before adolescence-or possibly
later - in genetically susceptible individuals. This unifying hypothesis em
phasizes, on the one hand, the role of a genetic-racial susceptibility and
the importance of environmental factors and, on the other, a possible aetio
logic heterogeneity and lack of specificity of the unknown endogenous and e
xogeneous agents. In this context, several environmental factors may be inv
olved in the aetiopathogenesis of MS in individuals who are susceptible to
the effect of exposure to these factors. Situations or events with biologic
al plausibility, such as childhood or adolescent infectious diseases, expos
ures to geographic and socio-cultural factors, nutritional habits, hypersen
sitivity, significant head and spinal trauma, and other factors may contrib
ute, at different times, to the putative acquisition of MS, trigger its ons
et, and modify its subsequent course. However, additional empirical evidenc
e is needed to clarify the complex interplay of genetic and environmental f
actors.