The median age at the time of death for white patients with muscular dystrophy is 10-12 years older than it is for black patients with the disease, according an analysis of data from all death certificates in the United States.
Moreover, in the 5 most recent years of the study’s 20-year time period, 24.5% of black males with muscular dystrophy (MD) had cardiomyopathy, compared with 12.8% of white males with the disease.
The findings, published online in the Sept. 14 issue of the journal Neurology, “might have been related to different prevalences of the various types of MD, different natural histories, or differences in environmental, genetic, or behavioral risk factors,” wrote Aileen Kenneson, Ph.D., of the Centers for Disease Control and Prevention’s National Center on Birth Defects and Developmental Disabilities, and her colleagues.
“However, it is possible that the use of corticosteroids and [noninvasive ventilation] was less common among black than white patients,” the investigators added.
Dr. Kenneson, who is currently affiliated with consulting firm McKing Consulting Corporation in Atlanta, and her associates looked at records from the National Center for Health Statistics’ Multiple Cause Mortality Files, which contain data from all death certificates in the United States, including immediate and underlying causes of death coded with the International Classification of Diseases.
The group confined their search to the period between 1986 and 2005; they excluded congenital MD from their analysis, since “the distribution of age at death [among these patients] indicated that they were clinically distinct” from other MD patient types.
Overall, there were 18,315 MD-associated deaths from 1986 through 2005; roughly three-quarters were male. The overwhelming majority (90.6%) were white, while 7.7% of deaths occurred among black patients. The remaining 1.7% were among patients identified as being from other races (Neurology 2010;75:982-9).
The authors found a significantly lower median age at death among black females with MD, compared with white females (51 years vs. 63 years, respectively).
They also noted that among white women, the proportion who were 45 years or older at death increased, from 78.7% in the first decade of the study period to 83.8% in the second decade.
“In comparison, only about 63% of black females were 45 years or older at death, and this proportion did not change over time,” the investigators wrote.
Among males, the median age at death was significantly lower among blacks than whites (23 years vs. 33 years, respectively).
The median age at death during the 20-year time span of the study increased significantly by 1.3 years annually for white males without cardiomyopathy and 0.2 years annually for those with cardiomyopathy. In contrast, the median age at death increased just 0.33 years annually for black patients without cardiomyopathy. Black patients with cardiomyopathy showed no significant gain in life expectancy at all.
The authors pointed out that although cardiomyopathy was more often reported among blacks than whites, this finding was true “even early in the study period before the widespread use of corticosteroids and [noninvasive ventilation] were likely to have had an effect.” Cardiomyopathy is a major contributor to morbidity and mortality in various types of MD.
That could mean that the increased incidence of cardiomyopathy among nonwhite patients is due to simple racial differences the course of MD, or to the higher frequency of cardiomyopathy among blacks in general, rather than a disparity in treatment.
Dr. Kenneson and her coauthors pointed out several limitations of this study. For one, she wrote, the database “did not include information about quality of life, so increases in age at death do not necessarily equate with improvements in quality of life.”
Secondly, “While the database contains some possible social effect modifiers, such as education and marital status, it does not include information to assess sufficiently other sociocultural variables, such as health insurance and family structure.”
The investigators acknowledged the potential for inaccurate data to be recorded on death certificates, although they thought the chance of this was likely remote.
Dr. Kenneson disclosed receiving research support from the CDC. Another investigator reported receiving advisory fees and research support from several pharmaceutical companies and muscular dystrophy-related support and research foundations.