The aim of this project is to study the role of transient receptor potential (TRP-) channel V1 (TRPV1+) fibers in the development of cutaneous inflammation induced by epidermal Ultraviolet-B damage. Moreover, in this project the investigators want to evaluate if the capsaicin-desensitization action can still be induced in a skin area pretreated with topical, local anesthetic lidocaine.
In this project the Ultraviolet- B pain model, a model using type B ultraviolet rays to induce a first-degree sunburn, will be used to induce a non-specific inflammation in the skin. This model is well-known to produce both peripheral and central hyperalgesia through sensitization of peripheral and central nociceptors. Capsaicin, the active substance in chili peppers, is currently used to treat peripheral neuropathic pain, and prolonged application of 8% capsaicin patch causes profound desensitization to painful heat stimuli and itch provocations. Therefore, the investigators would like to monitor the development of unspecific UVB-cutaneous inflammation and consequent neurogenic flare in a capsaicin pre-treated area. Moreover the investigators want to test if pre-treating the skin with lidocaine can reduce the pain associated with the capsaicin application without affecting its desensitization action.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Enrollment
44
Capsaicin patches (dosage form: patch 8% Qutenza) will be applied on 4x4 cm squared areas on the volar forearm. The patches will be left in place for 24h and 3 hours after which they will be removed.
Two circular areas (Ø 2 cm) on the forearm are irradiated with 2 x MED (Minimal Erythema Dose) dose of UVB using a calibrated UVB machine (290-320nm wavelength), Saal Mann Multi Tester (Mann Saal, LT SBC 400 Herford, Germany).
To deliver histamine, standard allergy skin prick test (SPT) lancets are applied. The lancets have a 1 mm shouldered tip adapt to introduce a small amount of test substance extremely locally and approximately at the dermo-epidermal junction.
Silvia Lo Vecchio
Aalborg, North Denmark, Denmark
Superficial blood perfusion measured by a Speckle contrast imager (FLPI, Moor Instruments, England).
Time frame: Changes from baseline to 7 days after intervention
Measurement of Warm Detection Thresholds and Heat thresholds by using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device.
Time frame: Changes from baseline to 7 days after intervention
Measurement of Pain to Supra-threshold Heat Stimuli by using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device.
Time frame: Changes from baseline to 7 days after intervention
Measurement of Mechanical Pain Thresholds and Sensitivity using a pin-prick set consisting of 8 needles each having a diameter of 0.6 mm and different force applications: 0.8, 1.6, 3.2, 6.4, 12.8, 25.6, 50.1 and 60.0 g.
Time frame: Changes from baseline to 7 days after intervention
Trans-epidermal Water Loss (TEWL) using a 2x2 cm probe to measure the humidity gradient of the skin.
Time frame: Changes from baseline to 7 days after intervention
assessment of pain rating by using a visual analog scales (VAS)
The subject will report the peak and average of the perceived pain sensation during the last 24 hours (on a VAs scale from 0 indicating 'no pain' to100 indicating 'worst imaginable pain').
Time frame: Change from baseline to 24 h
Itch rating by using a visual analog scales (VAS)
Itch is monitored for 9 minutes using a visual analog scale from 0 indicating 'no itch' to100 indicating 'worst imaginable itch.
Time frame: Changes from baseline to 7 days after intervention
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Cutaneous anaesthesia will be topically induced by using EMLA cream 5%, a local anaesthetic cream consisting of equal parts of lidocaine and prilocaine (1g contains 25 mg of lidocaine and 25 mg of prilocaine)