AAN 2016: MS among African-Americans
American Academy of Neurology (AAN) annual meeting, Vancouver, B.C., April 15-21, 2016
Multiple sclerosis is commonly regarded as a disease that predominantly affects people of white European descent, and was considered rare in other racial/ethnic groups, such as African-Americans. Such thinking can be self-fulfilling: if MS isn’t expected in African-Americans, doctors may be less likely to consider it as the diagnosis in someone with neurological symptoms.
However, recent studies have suggested that MS may be at least as common in African-Americans as white Americans. This is in contrast to blacks from other parts of the world, where MS is generally rare; this difference may be due to a combination of factors, such as genetics and environment (e.g. sun exposure, diet, exposure to disease-causing organisms, etc.).
A recent analysis of over 9 million people in a U.S. health insurance database over a three-year period found that the incidence (i.e. new cases) was 10.2 cases per 100,000 population per year among African-Americans, which was higher (6.9 per 100,000) than what was seen in white Americans (Langer-Gould and colleagues. Neurology 2013;80:1734-1739). MS was uncommon among Hispanics (2.9 per 100,000) and Asians (1.4 per 100,000).
The risk of MS was comparable in African-American males and the white population. However, the people at highest risk of MS were African-American women. Their MS risk was 60% higher than what was seen in the white American population.
Early signs of MS often differ between whites and blacks, which may contribute to under-recognition of MS in African-Americans. In one study, the most common early symptom of MS in African-Americans was inflammation of the spinal cord (transverse myelitis), which results in walking impairments (Langer-Gould and colleagues. J Neurol 2014;261:1349-1355). Another common problem is severe vision problems (optic neuritis), and recent studies have found that vision loss progresses more rapidly among African-Americans compared to other groups (Kimbrough and colleagues. Ann Neurol 2015;77:228-236).
So the general view is that the MS disease process is more severe and more rapidly progressive among African-Americans compared to other groups.
The perceived rarity of MS among African-Americans has had a number of important consequences. MS is understudied in blacks, in part due to low recognition of the disease and poorer access to healthcare. And clinical trials of new medications generally don’t include African-Americans, so little is known about how well the more aggressive disease course in African-Americans will respond to treatment.
A new study presented at AAN 2016 looked at changes in cognition (thinking, planning, problem solving, etc.) early in the disease course in African-Americans, Hispanics and white Americans (Schroeder and colleagues. AAN 2016; abstract P2.168). People newly diagnosed with MS underwent a battery of psychological tests. One test was the SDMT (for Symbol Digit Modalities Test), which evaluates “executive function”, such as planning, problem solving, attention and short-term memory. African-Americans and Hispanics had lower SDMT scores than whites, indicating greater cognitive dysfunction. However, SDMT scores were lower even in African-Americans and Hispanics without MS, indicating that the problem was not MS itself. And indeed, further analysis found that socioeconomic factors, such as income and education, were the reason for the differences in test scores, underscoring the importance of considering additional factors that may be confusing the picture and skewing the results.
The researchers concluded that MS does not appear to have a greater impact on cognitive functioning in African-Americans compared to other groups.
These results are in line with other recent studies. For example, an MRI study found that African-Americans had more brain lesions compared to white Americans (Howard and colleagues. PLoS One 2012;7:e43061). So MS appears to more inflammatory, which may explain in part why the disease is more aggressive and progressive in African-Americans. However, despite all the inflammation in the brain, there was no difference in the rate of brain tissue loss (called atrophy) in African-Americans compared to white Americans. Since MS treatments target this inflammation, this finding underscores the importance – especially true for African-Americans – of treating MS as soon as possible.
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