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Axonal hyperexcitability after combined NGF sensitization and UV ‐ B inflammation in humans
Author(s) -
Rukwied R.,
Weinkauf B.,
Main M.,
Obreja O.,
Schmelz M.
Publication year - 2014
Publication title -
european journal of pain
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.305
H-Index - 109
eISSN - 1532-2149
pISSN - 1090-3801
DOI - 10.1002/j.1532-2149.2013.00423.x
Subject(s) - hyperalgesia , nociceptor , sensitization , threshold of pain , nociception , visual analogue scale , nerve growth factor , medicine , axon reflex , erythema , stimulation , anesthesia , intradermal injection , neuropathic pain , allodynia , immunology , receptor
Background Both nerve growth factor ( NGF ) and ultraviolet‐B ( UV ‐ B ) irradiation sensitize nociceptive nerve endings and increase axonal excitability of nociceptors. Combining NGF and UV ‐ B treatment is supra‐additive for sensory sensitization and even caused spontaneous pain in about 70% of the subjects. Methods UV ‐ B irradiation was performed at day 21 after intradermal NGF injection in 13 volunteers. Pain thresholds, electrically induced axon reflex erythema and pain (1.5‐fold pain threshold, 5–100 Hz) was analysed at days 22, 24, 28, 35, 49 and 70 and correlated to hyperalgesia and spontaneous pain. Results Electrical pain threshold after combined NGF / UVB was reduced below single treatment at 24 h but not at 72 h post‐ UV ‐ B irradiation. At the NGF / UV ‐ B site, electrical pain was enhanced at all frequencies compared with single NGF and UV ‐ B sites at 24 and 72 h with pain ratings exceeding control values about twofold to threefold [65 ± 7 vs. 25 ± 8 visual analogue scale ( VAS ) (24 h) and 55 ± 9 vs. 22 ± 5 VAS (72 h)]. Hyperalgesia to electrical stimulation correlated with hyperalgesia to pinprick ( S pearman r = 0.44; p < 0.001, B onferroni corr.) and supra‐threshold heat ( S pearman r = 0.55; p < 0.001) stimulation at 24 h only. Electrical pain thresholds at the NGF / UV ‐ B site weakly correlated to spontaneous pain levels ( S pearman r = 0.3; p = 0.025, without B onferroni correction). In contrast, electrically induced pain or axon reflex erythema did not correlate to spontaneous pain levels. Conclusions The combination of NGF and UV ‐ B increases axonal excitability that contributes to hyperalgesia and might also facilitate ongoing spontaneous pain.