A new study reported by the Centers for Disease Control and Prevention (CDC) shows that survival time has significantly increased for certain categories of people with muscular dystrophy (MD) but that race and cardiac status have a large impact on survival.
The good news from this study is that life span is increasing for all Americans with MD who do not have cardiomyopathy (heart muscle deterioration). White American males with MD without cardiomyopathy experienced an increase in median life span of 26 years between 1986 and 2005. The life span for black American males with MD but no cardiomyopathy increased by six years over the same time period.
However, the study also showed that — consistent with statistics for black Americans with other diseases — black Americans with MD have shorter life spans than whites with MD.
The reasons for these racial disparities are unclear, although differences in access to specialty care, as well as biological and cultural factors, could play a role. The study did not attempt to uncover any reasons for these findings.
The study, which looked at MD-associated deaths between 1986 and 2005, is limited by the fact that it relied exclusively on death records, which contain only certain types of information that are not always accurate. Another limitation is that the study combined data related to deaths from all forms of MD except congenital MD.
Combining data on several forms of MD is particularly problematic, since the various forms of the disease have different effects, rates of progression, degrees of severity, and gender distributions. Conclusions about life expectancy for individual forms of MD cannot be drawn from this study.
About the new findings
Epidemiologist Aileen Kenneson and physician and public health specialist Ajay Vatave, both at the National Center on Birth Defects and Developmental Disabilities at the CDC in Atlanta, and Richard Finkel, a neurologist at Children's Hospital of Philadelphia (CHOP), reported the findings in the Sept. 14, 2010, issue of Neurology. Finkel co-directs the MDA clinic at CHOP and is a member of MDA's Medical Advisory Committee.
The investigators analyzed the death records of 18,315 people who died of MD-associated causes in the United States between 1986 and 2005; an MD-associated death was defined as any death that listed MD as either an immediate or underlying cause of death. Of those who died of MD-associated causes during this period, 90.6 percent were white, 7.7 percent were black, and 1.7 percent were other races.
The researchers found that — across the board — race and the presence or absence of cardiomyopathy made significant differences in length of life with MD. White patients with MD lived longer than black patients, and those without cardiomyopathy lived longer than those with cardiomyopathy.
Highlights of the findings include the following.
Meaning for people with MD
The study shows there were significant gains in life expectancy for subsets of patients with MD between 1986 and 2005.
The continued impact of cardiomyopathy on life span in MD suggests that increased surveillance for cardiac complications of MD and perhaps earlier or more intensive treatment of these conditions, may be warranted.
MDA is supporting research in this area, including two clinical studies through its Duchenne Muscular Dystrophy Clinical Research Network. (See DMD Clinical Research Network Studying Dystrophin-Deficient Heart.)
The CDC study has little value for predicting survival time for a specific form of MD because the data were combined for all forms of MD included in the study.
Nicte Mejia and Rachel Nardin, both neurologists at Massachusetts General Hospital in Boston, wrote an accompanying editorial to the CDC study, in which they speculated on the study's implications, particularly for the racial disparities in life span that it revealed.
They note that inequities in the delivery of health care in the United States and the "multiple ways in which race constrains access to care" seems the most likely explanation for the black-white survival time gap.
For example, they say, the black-white gap in insurance coverage is shrinking but nonelderly black patients remain 1.5 times more likely than their white counterparts to lack any type of insurance. Black patients rely on Medicaid about twice as frequently as white patients, they say, noting that the access to specialty care (such as cardiology) is not as good for Medicaid patients as it is for those with private insurance.
In addition, they point out that the CDC study found that white patients were more likely to die at home or in long-term care facilities or hospice, while black patients were more likely to die in, or en route to, acute-care hospitals or emergency rooms, suggesting later stage care.
The editorial writers say that racial differences in the prevalence and natural history of different types of MD could conceivably account in part for the racial disparities in survival time, but that such racial patterns in MD have not been documented to date.
They speculate that race could be correlated with different cultural beliefs, educational levels, social support systems or even environmental exposures that could influence disease outcomes.
The findings, they say, "challenge neurologists to study and address differences in outcome and care not explained on clinical grounds" and to study quality of life for patients with MD who are living longer.
Valerie Cwik, neurologist and MDA's medical director, said, "We are pleased to see that advances in medical care have led to improvements in life expectancy for at least some of those affected by muscular dystrophy, but we will certainly take the results of this study into consideration as we continue to strive to improve both quality and quantity of life for those living with neuromuscular diseases."
Since 1950, MDA has supported a nationwide network of clinics dedicated to providing multidisciplinary care for all individuals with neuromuscular diseases, regardless of race, gender, ethnicity or ability to pay.