title: Psychophysical measurements of itch and nociceptive sensations in an experimental model of allergic contact dermatitis.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Parul S
authors.initials: PS
authors.lastname: Pall
authors.affiliation: Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Olivia E
authors.initials: OE
authors.lastname: Hurwitz
authors.affiliation: Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Brett A
authors.initials: BA
authors.lastname: King
authors.affiliation: Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut. Electronic address: robert.lamotte@yale.edu.
authors.forename: Robert H
authors.initials: RH
authors.lastname: LaMotte
mesh_terms: D000276:Adjuvants, Immunologic / Q000009:adverse effects; D003503:Cyclobutanes / Q000009:adverse effects; D017449:Dermatitis, Allergic Contact / Q000150:complications* / Q000188:drug therapy / Q000209:etiology / Q000523:psychology*; D005260:Female; D006632:Histamine / Q000009:adverse effects; D017442:Histamine Agonists / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology; D008297:Male; D008962:Models, Theoretical; D059225:Nociception / Q000187:drug effects / Q000502:physiology*; D017288:Pain Threshold / Q000187:drug effects; D010446:Peptide Fragments / Q000633:toxicity; D010812:Physical Stimulation / Q000009:adverse effects; D011537:Pruritus / Q000188:drug therapy / Q000209:etiology*; D011601:Psychophysics / Q000379:methods*; D012867:Skin / Q000473:pathology; D013256:Steroids / Q000008:administration & dosage; D013997:Time Factors
chemical_list: D000276:Adjuvants, Immunologic; D003503:Cyclobutanes; D017442:Histamine Agonists; D010446:Peptide Fragments; D013256:Steroids; C571042:bovine adrenal medulla 8-22; C020637:squaric acid dibutyl ester; D006632:Histamine
keywords: Allergic contact dermatitis; hyperalgesia; hyperknesis; itch; pain