Ying Han


March 2008

Document Type


Degree Name



Dept. of Public Health and Preventive Medicine


Oregon Health & Science University


Background: Multiple sclerosis (MS) is a chronic inflammatory autoimmune demyelinating disease, which has a profound impact on patients’ social roles and quality of life. The etiology of MS is thought to involve both environmental factors and genetic susceptibility. Several studies have implicated exposure to ionizing radiation as one risk factor for multiple sclerosis. Communities around Hanford, a former nuclear site, are concerned about autoimmune diseases attributable to radiation exposure. Eastern Washington State has been suspected to have a high MS prevalence, despite the lack of a systematic survey. Methods: This study examines the prevalence of multiple sclerosis for the 6-year period of 1998 to 2003 in twelve counties located around Spokane. Data were extracted from medical charts from the primary MS diagnosis and treatment center in Spokane, and a major outpatient treatment system in the city. We applied the capture-recapture technique to these two data sources and estimated the total number of MS cases in the region. Multiple linear regression models were constructed to assess the associations between each county’s MS prevalence and demographic and environmental factors. Results: A total of 1088 cases were identified through the medical records from the two MS diagnosis and treatment systems. The number of female MS cases in the combined list from two sources was 3.1 times the number of male cases. Based on capture-recapture methods, 1626 MS cases were estimated in the study area. In the whole study area, the observed crude MS prevalence was 196.8 (95% CI: 185.1 – 208.5) cases per 100,000 adults; capture-recapture methods yielded a higher estimate of 294.1 (95% CI: 272.1 – 316.0) per 100,000 adults. At the county level, multiple linear regressions indicated that mean per capita income and geographic latitude were associated with total observed MS prevalence; using estimates of total MS prevalence from the capture-recapture method, only mean per capita income was associated at the 0.05 significance level. Conclusion: This study confirmed the community’s perception of high occurrence of multiple sclerosis. The capture-recapture method using two sources indicated a substantial proportion of “hidden” cases may exist. The combined counts of directly observed MS cases provide a lower bound estimate (“floor”), whereas the estimated MS prevalence based on capture-recapture provides an estimate of the upper bound (or “ceiling”). Analysis of cases from a third source, such as the collective data from neurologist practices in the area, or from the local MS society, would allow more confident determination of the upper range of prevalence. In multivariate analyses, the association between income and MS prevalence may reflect access to health care and care seeking behavior. The high prevalence of multiple sclerosis in this region suggests several intervention opportunities, including health service planning to ensure sufficient and accessible resources for MS diagnosis and care (e.g., MRI facilities, outpatient clinics), and the need to maximize early detection and use of available drug therapies to slow the progression of disease.




School of Medicine



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