Megan Brooks

October 02, 2013

COPENHAGEN, Denmark — Retinal damage and vision impairment may happen faster in African-American patients with multiple sclerosis (MS) relative to white patients with the disease, a new study suggests.

Researchers found for example that while African- American healthy controls have a slightly thicker peripapillary retinal nerve fiber layer (RNFL) than healthy white persons, among patients with MS there was no such difference. African Americans in this study had a greater velocity of RNFL thinning per year of follow-up, and race also modified the effect of optic neuritis on vision loss in patients with MS.

"We've also seen that race modifies the effect of disease duration on visual acuity deterioration, and taken together, this shows that vision represents another domain of MS in which the manifestations appear to be more ominous for African-American patients," lead author Dorlan Kimbrough, MD, from Johns Hopkins University, Baltimore, Maryland, concluded. "The reasons for this are unclear, but this phenomenon certainly merits further investigation."

The study was presented here on opening day of the 29th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS). The senior author was Peter A. Calabresi, MD, director of the MS Center, Johns Hopkins University, Baltimore, Maryland.

Lower Risk, but More Severe Disease

"There is a longstanding epidemiological literature suggesting that while patients of African descent are less likely to develop MS, they tend to experience more severe manifestations of the disease when it occurs," Dr. Kimbrough told Medscape Medical News. Although some more recent studies have questioned these lower incidence findings, there is little doubt that the manifestations are in fact more severe among African Americans, he said.

"Some of the more severe manifestations include greater overall disability scores at diagnosis and during the disease course; more frequent transverse myelitis and ambulatory disability; elevated levels of biomarkers of inflammation; and worse MRI markers of inflammatory damage to brain tissue, all usually compared to Caucasian patients," Dr. Kimbrough explained.

"Because retinal damage and visual dysfunction are common in MS patients, we hypothesized that if MS is more aggressive in African-American patients, then one would expect to find worse quantitative measurements in terms of retinal architecture and visual dysfunction (compared to Caucasian patients)," he explained.

Using mixed effects regression models, the researchers compared high- and low-contrast visual acuity and longitudinally acquired spectral-domain optical coherence tomography (OCT) measures of retinal architecture in African-American and white patients with MS. They had OCT and visual acuity data on 693 patients with MS (83 African-American) and 137 healthy controls (31 African-American) from 3 academic medical centers.

Prior studies by Dr. Calabresi's group showed that scanning the retina with OCT yields information about the extent of brain damage in patients with MS and also gives clues as to how quickly the disease is progressing.

In the current study, at baseline, the prevalence of an optic neuritis (ON) history did not differ between African-American and white patients. In healthy controls at baseline, foveal thickness, macular thickness, and macular volume did not differ between African-American and white patients.

Among healthy controls at baseline, peripapillary RNFL baseline was 5.1 μm greater in African Americans than whites (P = .025). In patients with MS, however, there was no baseline difference in the RNFL of African Americans and whites.

During a median follow-up of 1.6 years, RNFL decreased 0.31 μm per year for white patients vs 1.1 μm per year for African-American patients (P = .005 and P = .003, respectively) after adjusting for history of ON, age, sex, and disease duration.

Visual acuity, when analyzed among patients with MS who did not have a history of ON, did not differ between African-American and white patients at any contrast level, the researchers say.

However, African-American patients with a history of ON had clinically significant vision loss beyond that of their white counterparts with prior ON (change, –1 line of Sloan letter acuity at both 100% and 2.5% contrast levels; P = .027 and P = .031, respectively), the researchers say.

"Our findings suggest that the rate of retinal thinning in African-American MS patients is greater than among Caucasian-American MS patients," which may be independent of ON history, Dr. Kimbrough told Medscape Medical News. However, an ON history may predispose African-American patients to a greater degree of visual impairment.

The effect of ON, an inflammatory attack on the optic nerve and retina, leads to greater vision loss in African-American patients compared with white patients, and this difference can't be explained by a higher frequency of ON in African-American patients: The rates of ON are the same between African-American and white patients, Dr. Kimbrough explained.

"The reasons for the apparently more severe disease course in African-American patients is unclear. The disparity represents an additional important concern for both patient care and future research," Dr. Kimbrough said.

Dr. Calabresi's group has been studying retinal changes in patients with MS for some time. In a prior study, they showed that patients with MS who exhibit new lesions early on in their disease experience relatively fast thinning of the ganglion cell and inner plexiform layers of the retina.

The study was supported by the National Institutes of Health. The authors have disclosed no relevant financial relationships.

29th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS). Abstract 60. Presented October 2, 2013.

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