Background/Purpose: The identification of axial spondyloarthritis (axSpA) remains challenging. The initial presentation is not always immediately apparent as an inflammatory disease, potentially leading to years of delay in diagnosis. Our hypothesis is that the delay is worse in African American (AA) patients who have a lower disease prevalence of axSpA and lower frequency of HLA-B27 positivity compared to other racial groups. This retrospective study assessed whether AA patients experience a longer delay in diagnosis from symptom onset to diagnosis of axSpA compared to other ethnic cohorts, and whether they exhibit any significant differences in disease characteristics.

Methods: All adult rheumatology patients evaluated between 2012-2022 with a diagnosis code for ankylosing spondylitis, sacroiliitis, undifferentiated spondyloarthritis, or inflammatory back pain were enrolled. Variables collected include age at diagnosis (years, yrs), time to diagnosis (months, m), ethnicity, sex, HLA-B27 status, CRP at diagnosis (mg/L), history of IBD, psoriasis, uveitis, and family history of axSpA. All enrolled subjects had to have radiographic and/or MRI evidence of sacroiliitis. Fisher’s exact test and Mann-Whitney test were performed to compare categorical variables and non-parametric continuous variables respectively, and a multivariate logistic regression analysis was performed to identify independently associated variables with studied outcomes.

Results: 29 AA and 100 sex-matched non-AA subjects were enrolled. The median time to diagnosis from symptom onset was similar at 36 m for both groups. The AA group was older at diagnosis (median 38 yrs [interquartile range {IQR} 26 – 48 yrs] vs 29 years [IQR 23 – 37 yrs], p = 0.03) with higher CRP (15 mg/L [IQR 6 – 32 mg/L] vs 4 mg/L [IQR 2 – 10.5 mg/L], p = 0.001), and lower HLA-B27 positivity rate (36.8% vs 70.5%, p = 0.008). Due to the difference in age at diagnosis, subjects diagnosed at 45 years of age or older were compared to those diagnosed at a younger age. Those diagnosed at an older age had higher proportions of AA subjects (42.3% vs 17.5%, p = 0.015) and HLA-B27 positivity (70.4% vs 31.2%, p = 0.004). A multivariate logistic regression analysis showed that older age at diagnosis (≥45 yrs) was associated with negative HLA-B27 (Odds Ratio [OR] 5.94, 95% Confidence Interval [CI] 0.52 – 7.61) but not with ethnicity. It was also linked to time to diagnosis but the effect was minimal (OR 1.01, CI 1.004 – 1.017).

Conclusion: The time to diagnosis was similar between AA and non-AA groups. However, AA subjects were statistically older at diagnosis; whether this implies a delay in diagnosis or a different disease phenotype is not clear. In addition, AA subjects had a statistically higher degree of CRP elevation and lower HLA-B27 positivity rates. Through a multivariate analysis, older age at diagnosis was associated with negative HLA-B27, and this effect negated the relationship between race and age of diagnosis. Further research is needed to understand the interplay between CRP levels, HLA-B27 positivity and race in terms of disease characteristics vs delay in diagnosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/diagnostic-delay-of-axial-spondyloarthritis-in-african-american-patients/