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Abstract:
Multiple sclerosis (MS) is distributed about the world in three zones of high, medium, and low frequency. All high- and medium-risk areas are among predominantly white populations. Migration studies indicate MS is already acquired by age 15 in high-risk endemic areas and that low-to-high migrants increase their risk from age 11 years. Therefore MS is an environmental disease ordinarily acquired in adolescence with a long incubation before symptom onset. Susceptibility is limited to the period from about age 11 to 47. In general, MS death rates have been declining over time while prevalence rates have increased. Incidence rates have also increased, however, in: northeastern Scotland; Turku, Finland; Hordaland, Norway; Rochester, Minn.; Lower Saxony; several areas of Italy. Incidence was unchanged in northernmost Norway. Conversely, incidence and prevalence rates have decreased in the Shetland-Orkneys; there was a cyclical pattern in incidence in Rostock, GDR; and there was a transient doubling of incidence in Iceland in the post-World War II decade. In the Faroe Islands, MS was absent before 1943 when a major point-source epidemic began, reaching an incidence rate of 10 per 100,000 population in 1945. This was followed by two consecutively smaller epidemics with respective peaks each about 12 years later, and there is now a new epidemic IV on these islands. Explanations for changing incidence of MS over time should bring us closer to solving the etiology of this disease.
Insights
Multiple sclerosis (MS) is an environmental disease typically acquired in adolescence, with susceptibility between ages 11 and 47. Changing incidence rates globally may offer clues to its cause.
Area of Science:
- Epidemiology
- Neurology
- Environmental Health
Background:
- Multiple sclerosis (MS) exhibits distinct geographical distribution patterns.
- Risk factors and acquisition timing suggest an environmental influence, particularly during adolescence.
- Susceptibility to MS appears to be time-limited, occurring between approximately 11 and 47 years of age.
Purpose of the Study:
- To analyze global trends in multiple sclerosis (MS) incidence and prevalence.
- To investigate factors influencing changing MS rates over time.
- To explore the relationship between environmental factors and MS etiology.
Main Methods:
- Review of epidemiological data on MS distribution across high, medium, and low-frequency zones.
- Analysis of migration studies to understand risk acquisition.
- Examination of temporal trends in MS incidence and prevalence rates in various global regions.
- Case study of MS epidemics in the Faroe Islands.
Main Results:
- MS prevalence has generally increased while death rates decline, though incidence is rising in specific regions.
- Migration studies indicate MS acquisition before age 15 in high-risk areas.
- The Faroe Islands experienced distinct MS epidemics following 1943, with cyclical patterns observed.
- Incidence rates vary significantly by region and time, with some areas showing decreases.
Conclusions:
- Multiple sclerosis (MS) is strongly suggested to be an environmental disease acquired during adolescence.
- Understanding temporal and geographical variations in MS incidence is crucial for uncovering its etiology.
- Further research into environmental triggers is needed to explain the observed epidemiological patterns.