The impact of ethnic differences in response to capsaicin-induced trigeminal sensitization

Ethnic differences in the experience of pain, pain-related health care utilization and pain-reducing activities have been reported. Thus, evaluating of such variations is important in clinical and experimental pain. Since clinical pain is greatly influenced by disease-specific factors (severity, duration, type and treatment), evaluating ethnic differences in experimental pain models may not only provide some information about underlying mechanisms but also may predict or explain group differences in clinical pain. Migraine prevalence within ethnic populations is varied. Capsaicin injection to the forehead of healthy volunteers induces the state of an experimental trigeminal sensitization, which is one of the proposed mechanisms of migraine. The aim of the present study was to investigate ethnic differences between Caucasians and South Indians in this model of trigeminal sensitization. Thirty-two healthy male volunteers (16 South Indians and 16 Danish Caucasians) were included. Capsaicin (100 μg/0.1 ml) was injected intradermally to the right forehead skin. Pain sensitivity, secondary hyperalgesic area, and pressure pain threshold were assessed. Overall, the model showed significant greater pain responses in South Indians (8.75±1.25 cm pain intensity and 9.33±2.32 cm2 hyperalgesic area) compared to Caucasians (6.25±1.95 cm pain intensity and 6.25±1.41 cm2 hyperalgesic area). The model may provide important information for further clinical research, e.g. migraine or differences in mechanisms underlying trigeminal sensitization.