Neurologic Disease: Does Race Matter?

October 1, 2006

When it comes to disease risk, not all of us are created equal. Genetics, culture, diet, education, occupation, income, environment, or a combination of these factors can predispose some persons and ethnic groups to certain illnesses.

When it comes to disease risk, not all of us are created equal. Genetics, culture, diet, education, occupation, income, environment, or a combination of these factors can predispose some persons and ethnic groups to certain illnesses. For instance, diabetes mellitus is rampant among Pima Indians, and black populations have a higher incidence of hypertension than do white populations. Does this phenomenon also apply to persons with disorders affecting the CNS? Data are accumulating to suggest that racial and ethnic components need to be seriously considered when addressing certain neurologic conditions.

Different Strokes for different folks
Perhaps the most stunning and clear-cut data on racial influences-and disparity-in disease incidence concern ischemic events. Findings suggest that incidence and mortality are higher among black persons than among white persons,1-3 black and Hispanic persons are more likely than white persons to have stroke recurrence,4 black and Hispanic persons are more likely to be admitted for hospitalization with a diagnosis of acute brain lesion while white persons are more likely to be admitted for transient ischemic attack (TIA),5 and discrepancies in care may exist.6

The earliest population-based studies on stroke and ethnicity, conducted in the 1990s, pointed out that stroke incidence and associated mortality were higher in black persons than in white persons:

  • The Northern Manhattan Study compared the incidence of hospitalized and nonhospitalized first strokes in 210,000 black, white, and Hispanic persons living in the same urban community.1 The average age-adjusted stroke incidence per 100,000 population was 223 for black, 196 for Hispanic, and 93 for white persons. Compared with white persons, stroke incidence increased for black persons by 2.4-fold and for Hispanic persons by 2.0-fold.
  • The Greater Cincinnati/Northern Kentucky Stroke Study-the first large population-based metropolitan study to examine trends in stroke incidence and outcome in black and white persons2-found that most of the 1.3 million persons who died of or were hospitalized for stroke were black. Incidence of stroke among black persons in the Greater Cincinnati area was 288 per 100,000 population, compared with 179 per 100,000 among white persons living in Rochester, Minnesota.

The findings of these studies were confirmed by a recently published report by the CDC.7 The CDC study, like the earlier population-based studies, found that race matters when it comes to risk of stroke and heart disease. The prevalence of having 2 or more risk factors for stroke and heart disease was highest in black persons (48.7%) and Native Americans/Native Alaskans (46.7%), moderate for white persons (35.5%), and lowest for Asians (25.9%) (Table). Other factors, especially employment status and income level, also influenced stroke risk.

An earlier CDC report8 also noted a geographic variation in stroke risk and occurrence, with the highest incidence occurring in the so-called stroke belt: Kentucky (46.2%), Mississippi (45.8%), West Virginia (44.9%), Tennessee (43.2%), Louisiana (41.6%), North Carolina (40.4%), and Georgia (40%). Conjectures about contributors to the high incidence of stroke in the Southeast include softness of the drinking water, decreased antioxidant intake, a high incidence of hypertension, environmental toxins, and/or the low socioeconomic status of many residents in this area.5

TIMING AND CARE
Besides lifestyle habits and perhaps genetic predisposition, one of the reasons white persons may have an advantage over black or Hispanic persons in relation to stroke mortality and morbidity is that they are likely to have better timing. They are more likely to arrive at the emergency department within 3 hours of symptom onset. This was the finding of a review of data on black and white stroke patients admitted to the University of Cincinnati Medical Center.9 Furthermore, when black and Hispanic persons get to the hospital, they tend to present with more serious conditions than white persons do. A recent study from St Luke's-Roosevelt Hospital Center in New York City showed that white persons were more likely than black and Hispanic persons were to be admitted to the hospital with a diagnosis of TIA and that black and Hispanic persons were more likely to be admitted with a diagnosis of acute brain lesion.5

"It is possible that TIA is overdiagnosed in white persons and underdiagnosed in black and Hispanic persons," said the study's lead investigator, Daniel Labovitz, MD, associate professor of neurology and director of the Division of Cerebrovascular Disease in the Department of Neurology at New York University School of Medicine. "I think the 'take-home' message for practicing physicians, however, is that although black and Hispanic persons may show up at the hospital with a TIA less often than white persons, they are more likely to actually have a cerebral lesion. These patients may be more likely than white patients to go on to a full-blown stroke."

Once the patient is admitted to the hospital, does the quality of care vary according to race? Maybe. Jacobs and colleagues6 from the comprehensive stroke program at Wayne State University School of Medicine in Detroit culled data from a statewide hospital-based stroke registry and found that care was similar in many respects; however, a few differences were noted. Black persons were less likely than other persons to get a CT scan within 25 minutes of hospital arrival. They were also less likely to undergo cardiac monitoring or dysphagia screening and to receive smoking cessation counseling.

TIME TO ALZHEIMER DISEASE
Researchers are currently studying whether racial differences underlie Alzheimer disease (AD) pathology. Findings suggest that although the neuropathology appears to be similar between black and white persons,10 the rate of cognitive decline is slower in black persons.11 Indeed, a team from Washington University School of Medicine in St Louis was not able to identify a neuropathologic phenotype of AD that differed among races.10 They examined characteristics of AD: neurofibrillary tangles, senile plaques, Lewy bodies, cerebral infarcts, and cerebral amyloid angiopathy in autopsy specimens from 10 black and 10 age-, sex-, and dementia-matched white persons. The investigators found no important differences, however Barnes and colleagues11 from Rush University in Chicago found a correlation between race and rate of cognitive decline.

The Rush University team conducted extensive neuropsychological testing in 410 black and white patients with AD every 6 months for 4 years. The study showed that black persons scored lower than white persons at baseline on composite and specific measures of global cognition. However, their decline in episodic memory was about 25% slower than that of white persons.

AND MULTIPLE SCLEROSIS
Reports concerning multiple sclerosis (MS) and race are conflicting. Some investigators note greater impairment in eyesight and a shorter time between symptom onset and gait impairment in black patients than in white patients. Other studies report that progression of disability is similar if patients, regardless of race, are cared for at specialized MS centers. As with stroke, however, black persons may be further along in the disease process before MS is diagnosed.12-14

Marrie and colleagues12 used a patient self-report registry to examine the effect of race on mobility, hand, visual, and cognitive function and to compare the relationship of age and disability between black and white persons. Data were taken from 21,557 patients registered with the North American Research Committee on Multiple Sclerosis (NARCOMS). Regardless of race, a low level of education and income was associated with greater disability. Black persons were at greater risk for severe hand and visual disability; however, the severity of the disability was somewhat blunted after adjusting for socioeconomic status.

Black persons tended to have shorter intervals between symptom onset and MS diagnosis and were identified as having MS at a younger age than white persons. The investigators speculated, however, that rather than race as presumed, differences in the disease course might be the result of a delay in the initial presentation for evaluation and care. This suspicion was echoed in 2 other studies,13,14 including one of the first studies to investigate how MRI characteristics varied by race in persons with MS. In this study,13 reported at the annual meeting of the American Academy of Neurology in San Diego last spring, brain damage was more severe in black persons than in Hispanic and white persons.

The other study14 noted that black persons had more brain lesions. Black persons also were more likely than white persons to experience exacerbations of MS and were less responsive to interferon therapy.

COLLEEN B. LITOF is a freelance medical writer in Redding,Connecticut.

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