Enhanced Area of Secondary Hyperalgesia in Women with Multiple Stressful Life Events: A Pilot Study.
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OBJECTIVE: Stressful life events are associated with increased pain severity and chronicity. However, the mechanism underlying this association remains disputed. Recent animal studies suggest that chronic stress increases pain sensitivity and persistence by enhancing peripheral and central sensitization mechanisms. To test this hypothesis in humans, the authors examined whether sensitization is enhanced in healthy women reporting more stressful life events using the topical capsaicin test. METHODS: Thirty-two healthy young women reporting varying levels of stressful life events were invited for laboratory pain testing. Capsaicin was applied topically to the volar forearm. Measurements included capsaicin-induced spontaneous pain and area of secondary hyperalgesia in the region surrounding capsaicin application. Physiological (heart rate and skin conductance) and self-reported affective (emotional valence and arousal) states were also measured. RESULTS: The results indicate that more stressful life events predicted a linear increase in the area of secondary hyperalgesia (=0.40, p = 0.023, R2 = 0.16), but not the intensity of secondary hyperalgesia nor capsaicin-induced spontaneous pain. These findings suggest that life stressors may be associated with heightened central sensitization manifested by an increased area of secondary hyperalgesia. Additionally, life stressors were related to greater sympathetic cardiac, but not to affective responses to capsaicin-induced pain. CONCLUSION: This study shows that women reporting more stressful life events show a larger area of secondary mechanical hyperalgesia. These preliminary findings suggest that life stressors may facilitate pain processing by enhancing central sensitization.
