Age-related differences in the time course of capsaicin-induced hyperalgesia

The effect of age on hyperalgesia, one of the most common signs of injury, has not been previously examined in humans. A psychophysical study was cond ucted in 10 young (26.9 +/- 4.6 years) and 10 older (79.0 +/- 5.7 years) he althy volunteers to investigate the effect of age on the development of hyp eralgesia induced by topical application of capsaicin (0.1 ml, 5 mg/ml). Th e capsaicin patch (diameter 2 cm) was applied for 1 h. The intensity of cap saicin-induced spontaneous sensation, mechanical pain threshold, area of fl are, heat and punctate hyperalgesia were measured hourly for 3 h after the application. Older adults took a longer period to report first pain. There was no age effect on the magnitude of spontaneous sensation, hare size and area of heat hyperalgesia. The area of heat hyperalgesia rapidly decreased over time in both age groups. In marked contrast, the area of punctate hype ralgesia and associated reduction in the mechanical pain threshold were mai ntained in older adults over the entire 3 h test period, but resolved rapid ly in young adults. We conclude that, given the same intensity of noxious s timulation, older adults display a similar magnitude of hyperalgesia as you nger persons. However, once initiated, punctate hyperalgesia appears to res olve more slowly in older people. This finding may indicate age differences in the plasticity of spinal cord neurons following an acute injury. (C) 20 00 International Association for the Study of pain. Published by Elsevier S cience B.V. All rights reserved.