The effect of local anaesthetic on age-related capsaicin-induced mechanical hyperalgesia - A randomised, controlled study

Adults over 65 years exhibit a prolonged punctate hyperalgesia induced by topical application of capsaicin. The aim of this study was to investigate the role of peripheral afferent input in the slowed resolution of punctate hyperalgesia in older people. Twenty young (25.7 ± 4.8 years) and 19 old (74.9 ± 4.4 years) healthy adults were recruited, and subjects in each age group were randomly assigned to receive either EMLA cream (a local anaesthetic) (n = 10 in each age group) or Sorbolene treatment (n = 9 in the older group, n = 10 in the young group) after the development of punctate hyperalgesia. EMLA cream blocked punctate sensation and greatly reduced touch and warmth sensation. In comparison to Sorbolene treatment, EMLA abolished stroking but not punctate hyperalgesia in both age groups. The area of punctate hyperalgesia was maintained in older adults over 4 h, while it declined in the young. Older adults also reported reduced ratings to capsaicin-induced sensation and to stroking stimulation, and had a smaller area of stroking hyperalgesia. Ratings to punctate stimulation did not, however, differ between the age groups. Stoicism and cautiousness measured with Pain Attitude Questionnaire were negatively correlated with highest pain rating in the young, but not in the older groups. We suggest that the prolonged punctate hyperalgesia in older adults is possibly sustained by central mechanisms, indicating age differences in central plasticity following acute injury. The relationship between such age-related changes and the chronicity of pain in older adults should be further explored.