Highlights
- •Itch and pain were characterized in experimentally produced allergic contact dermatitis in humans.
- •Persistent, spontaneous itch peaked in 2 days and decreased during the ensuing week.
- •The inflamed skin exhibited enhanced pain and itch to heat and mechanical stimuli and increased itch to pruritic chemicals.
- •Cooling the inflamed skin reversibly blocked surrounding areas of mechanical alloknesis, hyperknesis, and hyperalgesia.
- •These sensory measurements will be useful in studies of neural mechanisms underlying inflammatory itch and pain.
Abstract
Allergic contact dermatitis (ACD) is a common condition that can significantly affect
the quality of life. Contact with allergens results in delayed hypersensitivity reactions
involving T lymphocytes, with associated skin inflammation and spontaneous itch and
nociceptive sensations. However, psychophysical studies of these sensations are lacking.
In the present study, we sensitized 8 healthy volunteers to squaric acid dibutyl ester
(SADBE). Two weeks later, 1 volar forearm was challenged with SADBE, and the other
with acetone vehicle control. Subsequently, participants rated the maximal perceived
intensity of spontaneous itch, pricking/stinging, and burning every 6 to 12 hours
for 1 week, using the generalized Labeled Magnitude Scale. In the laboratory, they
judged stimulus-evoked sensations within and outside the chemically treated area.
The SADBE- but not the acetone-treated skin resulted in 1) localized inflammation,
with spontaneous itch and nociceptive sensations peaking at 24 to 48 hours after challenge,
2) alloknesis, hyperknesis, and hyperalgesia to mechanical stimuli that were reduced
or eliminated by anesthetic cooling of the SADBE-treated area and restored on rewarming,
suggesting that sensations and dysesthesias are dependent on ongoing peripheral neural
activity, and 3) enhanced itch to intradermal injection of histamine, BAM8-22, or
β-alanine. This experimental model of T-cell-mediated inflammation may prove useful
in evaluating potential treatments of itch from ACD.
Perspective
In a model of allergic contact dermatitis, experimentally applied in humans, psychophysical
measurements were obtained of persistent, spontaneous itch and enhanced stimulus-evoked
itch and pain sensations. These sensory measurements will be useful in the identification
of the neural mechanisms underlying inflammatory itch and pain.
Key words
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Article info
Publication history
Published online: May 19, 2015
Accepted:
April 28,
2015
Received in revised form:
April 25,
2015
Received:
March 6,
2015
Footnotes
Research funding was provided by National Institutes of Neurological Disorders and Stroke P01 NS 047399 (R. LaMotte, PI). National Institutes of Neurological Disorders and Stroke had no role in the design of the study, the collection, analysis, and interpretation of data, or writing of the manuscript or its submission for publication.
The authors declare that there are no conflicts of interest.
Identification
Copyright
© 2015 American Pain Society. Published by Elsevier Inc. All rights reserved.
