Ethnic differences in capsaicin pain response in healthy subjects

Abstract

Ethnic differences in pain perception have been documented in a variety of clinical pain conditions, generally indicating that African Americans report greater pain and suffering when compared to whites. A growing body of experimental pain studies has also shown that African Americans report greater sensitivity (i.e., lower pain threshold) and reduced pain tolerance to a variety of quantitative sensory testing methods when compared to non-Hispanic whites. Forty-six healthy African American (n = 21) and non-Hispanic white (n = 25) subjects participated in an experimental screening session involving pain induction by topical high concentration (10%, .35g) capsaicin cream applied evenly to a 6.25cm2 area of skin on the back of the non-dominant hand. An occlusive dressing (TegadermTM) was placed over the site to maintain the capsaicin within the area of application. A warm thermode maintained a specific (40° C) skin temperature at the capsaicin site. Pain was induced for approximately 30 minutes, and verbal pain ratings were obtained at one minute intervals. Repeated Measures Analysis of Variance (ANOVA) revealed a significant difference in pain ratings over time (p = 0.001) and a rating by ethnicity interaction (p = 0.003). The average capsaicin pain intensity rating over the 30 minute period was 33.2 (SE = 4.0) for African Americans and 27.3 (SE = 3.7) for non-Hispanic whites; the final ratings (at 30 minutes) were 56.0 (SE = 5.7) for African Americans and 38.9 (SE = 5.2) for non-Hispanic whites. These findings indicate ethnic differences in capsaicin induced pain responses. These findings suggest ethnic group differences in the central and/or peripheral nervous system processing of a noxious chemical stimulus, which may have implications for understanding ethnic group differences in the experience of a variety of painful conditions.