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Large numbers of multiple sclerosis (MS) patients appear to be clustered in southeastern Wisconsin, and researchers are trying to find out why.

Healthcare records showed densities of MS patients as high as 1,000 cases per 100,000 persons in some Wisconsin zip codes, about of 353 per 100,000 population in the Midwest, reported Ahmed Obeidat, MD, PhD, of the Medical College of Wisconsin and Froedtert Hospital in Milwaukee, in a platform session at the 2022 annual meeting of the Consortium of Multiple Sclerosis Centers.

"The numbers were eye-opening," Obeidat told MedPage Today.

Some clusters of MS patients lived in areas near aluminum manufacturers, he observed.

"I noticed a large number of patients who came to see me in the clinic from areas that are at a distance from my practice location," Obeidat said. "Frequently I saw people coming from the same town or the same zip code, so I asked the question: is there a clustering of MS cases in Wisconsin?"

"When I looked at the areas where these patients came from, I noticed aluminum manufacturing plants," he continued. "I reviewed the literature and found previous reports of large amounts of of people living with MS and other neurodegenerative disorders."

Within 100 km of the Medical College of Wisconsin MS center, the density of MS patients per 100,000 population was 240. But in that 100-km radius, some areas reflected densities as high as 1,105 per 100,000. Ten zip codes had densities over 478 per 100,000. Overall, 67 of 110 zip codes within 100 km showed a density higher than 240 per 100,000.

Obeidat and colleagues used files from MS patients in the Froedtert Hospital and Medical College of Wisconsin Health Network and incorporated 2010 census data to compile population numbers. Zip codes further than 100 km away from the MS center or with fewer than 10 diagnosed MS patients were excluded.

"If anything, we are underestimating the overall numbers, because we have access only to the cases we follow at our health system," Obeidat noted.

The researchers identified 6,697 MS patients (73% female), then generated heat maps for total MS patients and MS patients per 100,000 population. Dense groups of patients lived near the MS center, but clusters also emerged in other areas.

"We noted several other areas with higher densities that cannot be solely explained by proximity," Obeidat said. "Two manufacturers near each other had clusters of MS patients."

People in Wisconsin are disproportionately affected by regional factors, including less vitamin D due to lower , Obeidat noted. But variables like that would affect latitudes across the entire state and would not account for specific differences in southeast Wisconsin, he pointed out. Smoking, obesity, and Epstein-Barr virus also have been tied to MS development.

The findings call for an investigation of local environmental factors, Obeidat stated.

"Our plan is to further explore the chemicals used in aluminum factories and study candidates for immune dysregulation," he said. "We think aluminum is a plausible associated chemical."

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