The latent period of multiple sclerosis: a critical review.

It is a widely held belief that multiple sclerosis is a disease with a long latent period that is preceded by heightened susceptibility before adolescence. There has, however, been little research focused on either the estimation of the latent period or determination of the susceptibility period. In this article, we present a critical assessment of the relevant literature on migrant studies, cluster studies, the Faroe Islands "epidemic," sibling study, and novel statistical approaches as they pertain to the pre-onset natural history of multiple sclerosis. We also discuss the roles of the latent and susceptibility periods in the design, analysis, and interpretation of epidemiologic studies.