New data shows MS to be more severe in African-Americans

The prevalence of MS differs among racial groups -- for instance, it is higher in Caucasians, lower in Asians and lower still in native Africans. In addition to affecting the chance of getting MS in the first place, racial factors may also affect the clinical aspects of MS once someone has developed the disease. In North America, this concept has motivated several studies comparing clinical characteristics of MS in African-Americans and Caucasian-Americans.

In general, these studies have found that while African-Americans have a lower risk of developing MS, they tend to have a worse outcome over time than Caucasian-Americans. For example, they may need a cane sooner or require nursing home care at a younger age. A study from the New York State MS Consortium (NYSMSC) reported a few years ago that although the EDSS scores of their registry participants did not significantly vary between these two groups, race did appear to affect outcome over time. In order to further explore the influence of race on MS outcome in a large population, the NYSMSC decided to reanalyze their data using a tool called the MS Severity Scale.

The MSSS is a 10-point scale that is based on EDSS but also takes into account disease duration. If two people with MS have the same EDSS but different disease durations, the one who has had the disease longer will have a lower MSSS, and vice versa. The scoring was based on a reference population of Europeans with MS, so someone with an MSSS of 1 or less would have a disease severity equivalent to the least severely affected 10% of that reference population. The concept of benign and malignant MS can also be studied using MSSS. In this study, benign MS was defined as MSSS < 0.45 (e.g., EDSS <=3.5 after 30 years) and malignant was defined as MSSS >= 9.6 (e.g., EDSS >= 6.0 at 7 years). MSSS scores can also be divided into 6 different severity grades (1 = least severe, 6 = most severe).

The NYSMSC group identified everyone in their registry who had a recorded EDSS score and disease duration of 1-30 years. This resulted in a study population of 5,809 Caucasian-Americans and 419 African-Americans. Each subject's earliest recorded EDSS was used to assign their MSSS number. African-Americans had a higher median MSSS score than Caucasian-Americans (6.0 vs. 4.8). African-Americans were also more likely to have MSSS scores in the top two severity grades and less likely to be in the bottom two grades than Caucasian-Americans. Similarly, African-Americans were more likely to have malignant MS and less likely to have benign MS. These differences were stronger in women than in men, because there were only a small number of African-American men in the analysis.

The findings held up even when adjusted for factors like age, disease subtype, disease duration, or whether the person was using a disease-modifying therapy at enrollment. It should be noted though that the length of time someone had been on a therapy was not analyzed, which might have skewed the results if it differed between the two groups.

This study supports the idea that race can affect MS outcome, and in particular strengthens the conclusion that African-American ancestry is correlated with greater severity. Which factors underlie this correlation are not yet known, but further study may provide some leads that could then be translated into strategies or therapies to halt or delay progression.