Disproportionate Residence of Multiple Sclerosis Patients in Southeast Wisconsin: A Clue to Environmental Factors?

Background: Environmental and lifestyle factors can contribute to the development of multiple sclerosis (MS), along with genetic predisposition. Earlier studies reporting on geographic MS clusters support the hypothesis that the location of residence can affect exposure to various organic and inorganic substances linked to the development of MS.

Objectives: To investigate for possible location clusters of MS patients in Southeast Wisconsin to explore the potential for environmental exposures.

Methods: All MS diagnosed patient files within the Froedtert and Medical College of Wisconsin health network were retrieved using the i2b2 database and Honest Broker toolkit. Patient ZIP codes were utilized to extrapolate state and city data; data from ZIP codes outside of Wisconsin were excluded. 2010 United States Census ZIP Code Tabulation Area data was used to compile population numbers by ZIP code in Wisconsin. Microsoft Excel 365 (version 2108) was used to generate heatmaps for total MS patients, MS patients per 100,000 population, and Wisconsin population by ZIP code.

Results: A total of 6674 patients were identified (73% Female) and clustered near the MS center (ZIP 53226), which is expected due to proximity to patients served. The density of MS patients per 100,000 population within 100 kilometers of the MS center was 240. Disproportionalities were noted in patient density when compared to total population data. Twenty highest MS densities per 100,000 by ZIP codes within 100 kilometers of the MS center were: 53046 (1105), 53007 (872), 53033 (661), 53122 (632), 53295 (552), 53040 (552), 53095 (511), 53090 (495), 53226 (492), 53037 (491), 53091 (485), 53022 (478), 53069 (474), 53223 (462), 53108 (459), 53075 (455), 53153 (452), 53089 (444), 53051 (437), 53213 (432).

Conclusions: To our knowledge, this is the first study to examine clusters of MS patients in Wisconsin. We report disproportionate densities of MS patients cared for within a single large academic center. Patients were clustered near the hospital center; however, we noted several areas further away with higher densities that cannot be solely explained by proximity. Recent studies have discovered high levels of aluminum in MS brain tissues. We noted clusters of MS patients near the ZIP code 53095, a location where a major aluminum factory operated until 2001. Our findings call for further investigations for potential environmental exposures which could be contributing to the disproportionate distribution of MS cases.