Environmental changes and epidemiology of multiple sclerosis in the French West Indies.

Multiple sclerosis (MS) emerged in the French West Indies (Martinique and Guadeloupe) at the beginning of the 1990s with an incidence for the period 1992-2007 of 1.27/100,000 (95% CI, 1.16-1.38). Its incidence, which is continuously increasing, reached 2.27/100,000 (95% CI, 1.92-2.62) in Martinique for the period 2002-07. Neuromyelitis optica (NMO), in contrast, has a stable incidence of 0.19/100,000 (95% CI, 0.15-0.23) resulting in a gradual increase in the MS/NMO ratio, which was 8.35 for the period 2002-07. MS initially affected the female population with a female/male incidence ratio of 8.43 for the period 1992-97, which gradually fell to 2.63 for the period 2002-07 due to the increased incidence of MS in men. Several environmental factors are involved in the emergence of MS: (1) the migration of the French West Indian population to mainland France resulted in an excess incidence of MS in the migrants; (2) a decrease in sun exposure, a risk factor for MS, related to the changing lifestyle of the French West Indian population has been demonstrated in a case-control study; (3) at ecological level, enhanced hygiene associated with the eradication of intestinal helminthiases, known to induce immune system tolerance, is also strongly suspected with regard to MS emergence.