Multiple sclerosis in New Orleans, Louisiana, and Winnipeg, Manitoba, Canada: Follow-up of a previous survey in New Orleans, and comparison between the patient populations in the two communities

Abstract

A follow-up and re-evaluation of the 1951 epidemiologic survey of multiple sclerosis in New Orleans was conducted during 1964 and 1965. The purpose of this study was to reappraise all case reports of the previous survey in order to evaluate the degree of accuracy of the 1951 survey. Additional objectives of this investigation were to provide information on survivorship patterns and the natural history of multiple sclerosis in New Orleans and to establish a comparison with the corresponding aspects of the disease in Winnipeg, Manitoba, Canada where a similar study had been completed 2 yr before. All but one of the 69 patients examined in the previous survey were successfully traced in the follow-up study and their latest medical status was determined. Twenty-four of the 29 patients included in the 1951 survey as being in the group with “probable” multiple sclerosis were accepted as such in our follow-up study, and four in the “possible” and “unlikely” groups of the previous survey were reclassified to the “probable” group on the basis of our re-evaluation. An additional 31 patients, who in retrospect should have been eligible for the original study in 1951 but had not been examined then, usually because their condition had not yet been diagnosed, were also classified in the “probable” group in our study. Our revised total of patients in the “probable” group as of 1 Jan. 1951 was therefore 59, with a prevalence rate of 8.6 per 100,000 population. On the basis of our re-evaluation studies the ratio of prevalence rates in the two communities, which in the previous study had been computed at 6.6:1 (Winnipeg vs. New Orleans), is now estimated as about 4:1. For the “probable” group in our re-evaluation study in New Orleans, the female: male ratio was 1.2: 1, as compared to 2: 1 in Winnipeg. The estimated mean age at onset for all patients was 30 yr in New Orleans and 28 yr in Winnipeg. The rate of progression of the disease was similar in New Orleans and in Winnipeg, with the average duration of the disease estimated to be not less than 22 yr in New Orleans and 21 yr in Winnipeg. The average annual mortality rate in New Orleans was estimated as 0.23 per 100,000 population, and the Winnipeg: New Orleans ratio of mortality rates was estimated as 4: 1, which is the same as the ratio of prevalence in the two communities. The average annual incidence rate per 100,000 population in New Orleans was 0.45 for the 1940 through 1949 decade, and 0.39 for the 1950 through 1959 decade, the difference not being significant; the incidence rates for the same periods in Winnipeg were 1.6 and 1.5, respectively, with the Winnipeg: New Orleans ratio of incidence rates also close to 4: 1 for each decade. The prevalence of multiple sclerosis for metropolitan New Orleans was also determined as of 1 Jan. 1962. The number of patients in the “probable” group was estimated to be 83, with a prevalence rate of 9.6 per 100,000 population. The prevalence rate per 100,000 population in Winnipeg was 35.4 in 1960, and the Winnipeg: New Orleans ratio of prevalence rates remains close to the 4: 1 observed for 1951. In conclusion, our study reinforces the previous notion of a north-south difference in the frequency of multiple sclerosis, while it lends support to the impression that the natural history of multiple sclerosis in a southern community is essentially similar to that in a northern one. Although the explanation for the geographic variation in the distribution of multiple sclerosis is still not clear, the formulation of future etiologic hypotheses would be facilitated by a more exact determination of the distribution pattern of the disease throughout the United States. Further studies would therefore be needed. These could be less complex and still comparable for statistical purposes, by limiting the surveys to a critical review of hospital records only, in a large number of communities in the United States.