Ipsilateral and contralateral sensory changes in healthy subjects after experimentally induced concomitant sensitization and hypoesthesia.
BACKGROUND
In unilateral neuropathic pain. e.g. after peripheral nerve injury, both positive and negative sensory signs occur often, accompanied by minor but equally directed contralateral sensory changes. To mimic this feature, we experimentally aimed to induce concomitant c-fibre sensitization and block in healthy subjects and analyzed the bilateral sensory changes by quantitative sensory testing (QST) using the protocol of the German Research Network on Neuropathic Pain.


METHODS
Twenty eight healthy subjects were firstly randomized in 2 groups to receive either topical capsaicin (0.6%, 12 cm2, application duration: 15 min.) or a lidocaine/prilocaine patch (25/25 mg, 10 cm2, application duration: 60 min.) on the right volar forearm. Secondly, 7-14 days later in the same area either at first capsaicin (for 15 min.) and immediately afterwards local anesthetics (for 60 min.) was applied (Cap/LA), or in inversed order with the same application duration (LA/Cap). Before, after each application and 7-14 days later a QST was performed bilaterally.


METHODS
Wilcoxon-test, ANOVA, p < 0.05.


RESULTS
Single application of 0,6% capsaicin induced thermal hypoesthesia, cold hypoalgesia, heat hyperalgesia and tactile allodynia. Lidocaine/prilocaine alone induced thermal and tactile hypoesthesia as well as mechanical and cold hypoalgesia, and a heat hyperalgesia (to a smaller extent). Ipsilaterally both co-applications induced a combination of the above mentioned changes. Significant contralateral sensory changes occurred only after the co-application with concomitant sensitization and hypoesthesia and comprised increased cold (Cap/LA, LA/Cap) and mechanical detection as well as cold pain threshold (LA/Cap).


CONCLUSIONS
The present experimental model using combined application of capsaicin and LA imitates partly the complex sensory changes observed in patients with unilateral neuropathic pain and might be used as an additional surrogate model. Only the concomitant use both agents in the same area induces both positive and negative sensory signs ipsilaterally as well as parallel contralateral sensory changes (to a lesser extent).


BACKGROUND
ClinicalTrials.gov Identifier NCT01540877 , registered on 23 February 2012.
Department of Neurology, BG University Hospital Bergmannsheil GmbH, Ruhr University Bochum, Bürkle-de-la-Camp-Platz 1, D-44789, Bochum, Germany. elena.krumova@rub.de.
Elena K
EK
Enax-Krumova
Department of Pain Medicine, BG University Hospital Bergmannsheil GmbH Bochum, Ruhr University Bochum, Bochum, Germany.
Stephanie
S
Pohl
Department of Pain Medicine, BG University Hospital Bergmannsheil GmbH Bochum, Ruhr University Bochum, Bochum, Germany.
Andrea
A
Westermann
Department of Pain Medicine, BG University Hospital Bergmannsheil GmbH Bochum, Ruhr University Bochum, Bochum, Germany.
Christoph
C
Maier
D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology*; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006987:Hypesthesia / Q000139:chemically induced / Q000503:physiopathology; D008012:Lidocaine / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009437:Neuralgia / Q000503:physiopathology*; D011318:Prilocaine / Q000008:administration & dosage / Q000494:pharmacology*; D018689:Sensory System Agents / Q000008:administration & dosage / Q000494:pharmacology*; D020886:Somatosensory Disorders / Q000139:chemically induced / Q000503:physiopathology*; D055815:Young Adult
D000779:Anesthetics, Local; D018689:Sensory System Agents; D011318:Prilocaine; D008012:Lidocaine; D002211:Capsaicin
Capsaicin; Contralateral sensory changes; Experimental pain model; Local anesthetics; Neuropathic pain; Pain mechanisms; Quantitative sensory testing; Sensory profiles; Translational pain research