Repetitive intradermal capsaicin: differential effect on pain and areas of allodynia and punctate hyperalgesia

• Published in: Somatosensory & motor research Vol. 17; no. 1; pp. 5 - 12
• Main Author: Witting, Peter Svensson, Lars Arendt-Nielsen, Troels S. Jensen, Nanna
• Format: Journal Article
• Language: English
• Published: England Informa UK Ltd 2000; Taylor & Francis
• Subjects: Adult; Afferent Pathways - drug effects; Afferent Pathways - physiopathology; Capsaicin - pharmacology; Capsaicin Allodynia Hyperalgesia Mechanism Repetitive; Female; Humans; Hyperalgesia - chemically induced; Hyperalgesia - physiopathology; Injections, Intradermal; Male; Nociceptors - drug effects; Nociceptors - physiopathology; Pain Measurement; Pain Threshold - drug effects; Pain Threshold - physiology; Spinal Cord - drug effects; Spinal Cord - physiopathology; Synaptic Transmission - drug effects; Synaptic Transmission - physiology
• ISSN: 0899-0220; 1369-1651
• DOI: 10.1080/08990220070256

This study examined the effect of repeated intradermal capsaicin injections on capsaicin pain intensity and areas of allodynia and punctate hyperalgesia. Seventeen healthy volunteers participated in four sessions separated by at least 5 days. Each session included four intradermal injections of 10 mug of capsaicin. In one session injections were given with 0.5 cm and 6 min intervals, in a second with 0.5 cm and 15 min intervals, in a third with 0.5 cm and 24 min intervals, and in a fourth session with 4 cm and 15 min intervals. Following each injection capsaicin pain intensity was measured in the first 5 min, the area of allodynia at 5 min and area of punctate hyperalgesia at 10 min. With 6 min and 0.5 cm between repeated injections, capsaicin pain intensity decreased significantly whereas areas of allodynia and punctate hyperalgesia increased. In contrast, both capsaicin pain intensity and areas of allodynia and punctate hyperalgesia increased when the interval between injections was 24 min and 0.5 cm or 15 min and 4 cm. With 15 min and 0.5 cm between injections, capsaicin pain intensity did not change, whereas areas of allodynia and punctate hyperalgesia increased. There were no significant relations between capsaicin pain intensity and areas of allodynia and punctate hyperalgesia after first injections. The findings indicate that the response to intradermal injection of capsaicin is dependent on the time and distance between injections. The lack of significant relation between capsaicin pain intensity and area of allodynia and punctate hyperalgesia suggests that the two phenomena are mediated by different central mechanisms.