AS More Severe in Blacks Than in Whites or Latinos in US, Study Finds

Rachita Narsaria, MD avatar

by Rachita Narsaria, MD |

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African-Americans are more likely to develop severe ankylosing spondylitis (AS), with greater loss of function and higher disease activity, than either white Americans or Latinos, a new study revealed.

The study, “Ethnicity and disease severity in ankylosing spondylitis a cross-sectional analysis of three ethnic groups,” was led by researchers at the University of Texas-Health McGovern Medical School in Houston, and published this month in the journal Clinical Rheumatology.

Researchers analyzed 925 people with ankylosing spondylitis of different ethnicities — 805 Caucasians, 63 Latinos, and 57 African-Americans — evaluating disease activity, disease severity as seen in X-rays and imaging tests, and the amount of joint function lost due to the disease. All were enrolled in the Prospective Study of Outcomes in Ankylosing Spondylitis (PSOAS), an  NIH-funded longitudinal study of people with this chronic inflammatory disease, a form of arthritis that primarily affects the spine but can cause pain and stiffness in other joints.

They also assessed the clinical characteristics and frequency of a disease biomarker, HLA-B27, a protein found on the surface of white blood cells that is used to diagnose ankylosing spondylitis.

Results found the protein in 62.5% of blacks in the s, 86.7% Latinos, and 85.3% Whites had the HLA-B27 protein.

Researchers also compared the three groups for baseline Bath Ankylosing Spondylitis Radiographic Index (BASRI) and modified Stokes Ankylosing Spondylitis Spine Score (mSASSS). These indices are standardized test questionnaires designed to assess ankylosing spondylitis severity.

Investigators found that the baseline scores of blacks on both BASRI and mSASSS were higher (mean 9.5 and median 38.2, respectively), as compared to whites (7.3 and 6.4) and Latinos (7.3 and 8.1), respectively. These scores also rose as the study progressed.

In addition, blacks also had greater functional impairment according to the Bath Ankylosing Spondylitis Functional Index (median 62.5), compared to ehites (median 27.8), and Latinos (median 38.1). They also had higher disease activity assessed by the Bath Ankylosing Spondylitis Disease Activity Index (median 5.9), compared to Whites (3.5) and Latinos (4.5).

The levels of two inflammation markers in the blood were also higher in blacks compared to whites or Latinos: the erythrocyte sedimentation rate was a median of 27.0 in blacks compared to  10.0 in whites and 17.0 in Latinos, and median C-reactive protein levels were 1.2 in blacks, 0.4 in whites, and 0.9 in Latinos.

When the results were adjusted for other variables which might affect the scores — e.g., smoking, education level, gender, disease duration, and use of drugs like TNF inhibitors — the higher BASRI and mSASSS scores still held, indicating greater disease severity.