Thirteen patients selected for temporal artery biopsies were younger than 50. Of those patients, one black patient had a positive biopsy result. Because the concept of patients younger than 50 years old developing GCA is controversial, the researchers excluded this patient from further analysis.
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The investigators found 16.1% of the 573 patients who were 50 years and older and underwent testing had biopsy-proven GCA (8.4% of black patients and 19.6% of white patients). The researchers found indeterminate results in 13 patients (two black and 11 white). The mean age of patients with biopsy-proven GCA was similar in white and black patients, with a mean difference of 1.3 years (95% CI, -3.9 to 6.7; P=0.61).
The investigators calculated that, for black patients, the crude annual incidence rate for biopsy-proven GCA was 2.9 (95% CI, 1.3–5.5) per 100,000. For white patients, it was 4.2 (95% CI, 3.0–5.6) per 100,000. When they performed a logistic regression analysis, the association between biopsy-proven GCA and white race persisted (OR, 2.5; 95% CI, 1.4–4.4; P=0.003). An adjustment for race yielded a rate per 100,000 population of 2.3 (95% CI, 1.2–3.5) for men and 4.4 (95% CI, 2.9–5.8) for women. When the researchers performed population-adjusted age- and sex-standardized incidence rates, they calculated rates of 3.1 (95% CI, 1.0–5.2) per 100,000 for black patients and 3.6 (95% CI, 2.5–4.7) per 100,000 for white patients. Although they were able to calculate an incidence rate ratio of 1.9 in women compared with men (95% CI, 1.1–3.4; P=0.03), the investigators found no significant difference between white and black patients (1.2; 95% CI, 0.6–2.4; P=0.66).
“I think the results are indeed surprising,” says Sebastian Unizony, MD, co-director of the Vasculitis and Glomerulonephritis Center at Massachusetts General Hospital, Boston. “However, with [some] reports suggesting otherwise and considering that in clinical practice the great majority of the patients are white—at least in my experience—the results need to be replicated. In the meantime, rheumatologists need to be aware that GCA in African Americans may not be as rare as previously reported and keep a high index of suspicion not to miss potential cases.”
Tanaz Kermani, MD, director of the University of California, Los Angeles, Vasculitis Program agrees. She notes, “There are other diagnoses, including other forms of vasculitis, that can cause inflammation of the temporal arteries and look like GCA. Further study is needed to confirm these findings. Meanwhile, physicians should continue to evaluate anyone with symptoms that are suspicious for GCA appropriately, with studies including biopsy regardless of the race.”