Cognitive Impairment in Early MS Not Linked to Ethnicity, US Study Suggests

Ethnicity does not seem to have an influence on the degree of cognitive impairment seen in patients at the early stages of multiple sclerosis (MS), a U.S.-based study suggests.

The study, “Race, ethnicity, and cognition in persons newly diagnosed with multiple sclerosis,” was published in the journal Neurology.

Most people with MS experience both physical and cognitive disability caused by chronic inflammation in the central nervous system, comprised of the brain and spinal cord.

Changes in cognitive function seen in the early stages of MS are known to help predict severe impairments in cognition later in the disease course. But researchers are still looking for factors that can help predict which patients are at higher risk for developing serious cognitive impairments.

It is believed that ethnicity plays a role in MS susceptibility rates.

Now, researchers at the University of Southern California, Keck School of Medicine, investigated whether a person’s ethnicity is a contributing factor for early changes in cognition.

To evaluate cognitive function, the team used the Symbol Digit Modalities Test (SDMT), a reliable tool used in MS and other neurological diseases. The test measures attention, processing speed, and working memory capacity, and can be used to evaluate changes in cognition over time.

The researchers used the oral version of the SDMT so as to exclude the effect of potential hand impairments in patients.

Participants were recruited from the MS Sunshine Study — a multi-ethnic, matched, case-control study of MS in southern California that analyzed the influence of vitamin D levels in disease incidence. For each patient, at least one healthy individual (control) with matched race/ethnicity, sex, and age was recruited.

Ultimately, data were collected from 1,174 adults, among whom 519 were white, 261 black, and 394 Hispanic. The Hispanic participants were mostly Mexican (78.9%) or of mixed-Mexican descent (3.4%), while most black participants were African-Americans born in the U.S. (97.2%). The majority of MS patients in the overall group were women (71%), with a mean age of 40.7 years at the time of the cognitive assessment.

Among white participants with MS, 64% had an annual income above the Californian median ($65,000), compared with 43% of black patients, and 44% of Hispanics. Compared with white and Hispanic patients, fewer black participants with MS completed college.

The SDMT results showed that MS patients had lower scores among all ethnic groups compared with controls. Those patients with black and Hispanic ethnicity had a lower mean SDMT — 47.3 and 53 — compared with white patients, with a score of 54.

Yet, the analysis showed that the relation between ethnicity and having MS on SDMT scores was not significant. Further analysis showed that MS patients of Hispanic or black ethnicity have a similar reduction in SDMT scores as the healthy controls.

“We did not find any evidence that MS causes more cognitive impairment in black or Hispanic patients early in the disease course compared to white patients,” the researchers said.

This finding suggests that differences in cognitive impairment among people with MS is most likely due to differences found in the underlying population.

“Lower absolute SDMT scores among black and Hispanic patients compared to white patients highlight underlying U.S. population differences rather than differences in MS disease severity,” the researchers said.

Newly diagnosed MS patients “are more likely to have subtly impaired cognitive function than controls regardless of race/ethnicity,” the team concluded.

The researchers suggested that “improving opportunities for higher educational attainment and higher incomes for black and Hispanic participants in the United States would likely reduce racial/ethnic disparities in cognitive performance.”