Osteoporosis Rates Among African-Americans with RA
Minorities have historically been under-represented in medical research and clinical trials, for a variety of reasons; reasons that have been debated among medical ethicists, sociologists and others. Some of the reasons cited include ethnocentrism – Caucasian male scientists design experiments for and recruit Caucasian men; mistrust – minorities do not trust that Caucasian scientists have their best interests at heart (see the Tuskegee Syphilis Study sidebar); and lack of referral – physicians fail to refer minority patients to trials.
One group of researchers, funded by the National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases and the Arthritis Foundation, is doing its part to examine potential racial and ethnic disparities in rheumatoid arthritis (RA). The CLEAR (Consortium for the Longitudinal Evaluation of African Americans with Early Rheumatoid Arthritis) registry has enrolled more than 300 African-Americans with RA of no more than two years’ duration from five institutions across the southeastern United States. This longitudinal, observational study is designed to understand the factors that determine the development and severity of RA in African-Americans. This is the first research program designed specifically to evaluate RA among African-Americans. These volunteers, predominantly women, have given generously of their time for the advancement of the understanding of early RA and its impact on African-Americans.
One small portion of the CLEAR study is measuring bone density and observing the effects of RA and RA medications on bone density.
What problem was studied?
The goal of this observation was to determine the prevalence of osteopenia and osteoporosis among CLEAR participants. The presence or absence of osteopenia and osteoporosis are not determined by absolute numbers on bone mineral density (BMD) tests. Rather, their diagnoses are based on a statistical approach. People whose BMD is 1 – 2.5 standard deviations (SD) below the reference mean for young adults are diagnosed with osteopenia; those whose BMD is ≥2.5 SDs below the young adult mean are diagnosed with osteoporosis.
The problem arises when you look more closely at the reference data. The large pools of otherwise healthy people from whom BMD measures are typically drawn are matched for sex, but are not always matched for race or ethnicity to the person being tested. It was found in a previous study that young, healthy African-Americans have approximately 10 percent greater BMD than young healthy Caucasians. So, it was hypothesized that the assessment of bone health in this group of African-American RA patients would be highly dependent on the race or ethnicity of the reference population.
The CLEAR study investigators (including Arthritis Foundation-funded researchers Ted R. Mikuls, MD, MSPH; Kenneth G. Saag, MD, MSc; and Jeffery Curtis, MD, MPH) made determinations of osteopenia and osteoporosis based on both the standard reference data and reference data that were specifically selected to include only the race-matched reference population.
What was done in the study?
Using dual-energy X-ray absorptiometry (DEXA), researchers measured the BMD of the femoral neck (the top of the thigh bone where it connects to the ball portion of the hip joint) and lumbar spine of 172 study participants. Using a statistical computer program and two sets of normative data, the DEXA results were compared against a Caucasian population and a race-matched (African-American) reference population.
What were the study results?
Using the Caucasian reference data, approximately one-third of patients were classified as having either osteopenia or osteoporosis (40 people with osteopenia; 8 with osteoporosis). When African-American normative data were used instead, more than one-half were classified as having osteopenia or osteoporosis (67 people with osteopenia; 27 with osteoporosis).
What’s the relevance to people with RA or osteoporosis?
The prevalence rates of osteopenia and osteoporosis found in the study are not disproportionately higher than those seen in African-Americans without RA. This lets us know that osteoporosis is not a big risk at least early in the course of RA, although other study results reveal that it is a risk after prolonged disease.
Study results show that African-Americans are at risk of receiving different diagnostic classifications of osteoporosis than Caucasians based simply on the normative data used (which may differ from one physician’s office to another). What is not known, however, is how these racial differences in BMD correlate with fracture risk, the real end-point of concern.
All these study results point to the need for larger studies examining fracture risk in minority populations, and in the meantime, adoption of a standardized approach to osteopenia and osteoporosis diagnosis in these populations.
Mikuls TR, Saag KG, Curtis J, et al. Prevalence of osteoporosis and osteopenia among African Americans with early rheumatoid arthritis: the impact of ethnic-specific normative data. J Natl Med Assoc 2005;97:1155–60. PMID: 16173331