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Rheumatology Advance Access originally published online on July 16, 2008
Rheumatology 2008 47(9):1417-1421; doi:10.1093/rheumatology/ken251
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© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Contralateral hyperalgesia and allodynia following intradermal capsaicin injection in man

N. G. Shenker1, R. C. Haigh2, P. I. Mapp3, N. Harris4 and D. R. Blake4,5

1Department of Rheumatology, Addenbrooke's Hospital, Cambridge University Hospitals, Cambridge, 2Department of Rheumatology, Royal Devon and Exeter Hospital, Exeter, 3Academic Department of Rheumatology, University of Nottingham, City Hospital, Nottingham, 4Department of Rheumatology, Royal National Hospital for Rheumatic Diseases and 5School for Health, University of Bath, Bath, UK.

Correspondence to: N. G. Shenker, Box 204, Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge CB2 0QQ, UK. E-mail: nicholas.shenker{at}addenbrookes.nhs.uk


  Abstract

Objectives. Contralateral responses to unilateral stimuli have been well described in animal models. These range from central sensitization to peripheral inflammatory responses. Our aim was to test for contralateral responses following unilateral intradermal capsaicin injection in man.

Methods. Three groups were investigated. A healthy volunteer group (1) was injected with capsaicin into the volar aspect of one forearm. A group of patients with RA (2) was also injected with capsaicin. A control group of healthy volunteers (3) was not injected with capsaicin. All groups were tested for hyperalgesia and allodynia every 10 min for 1 h following the injection using quantitative sensory testing.

Results. A total of 9/14 healthy volunteers (Group 1) and 10/14 patients with RA (Group 2) demonstrated contralateral sensitization that subsided within 1 h following intradermal capsaicin injection. A total of 2/23 control subjects (Group 3) demonstrated positive responses with the monofilaments. The frequency of the contralateral responses in the experimental groups compared with the control group is significant (P < 0.05). The peak hyperalgesia was relatively delayed contralaterally compared with the ipsilateral side (35 min vs 15 min). The area of sensitization, where present, was reduced compared with the ipsilateral side (5–50%).

Conclusions. This is the first demonstration of a contralateral response following a unilateral stimulus in man. Bilateral neural pathways mediating contralateral responses may have a role in the pathophysiology of chronically painful or inflammatory diseases and a confounding influence on using the contralateral limb as a control experimentally. We did not find that a systemic inflammatory disease sensitized for this phenomenon.

KEY WORDS: Human, Capsaicin, Contralateral response, Hyperalgesia, Allodynia, Rheumatoid arthritis, Neurogenic inflammation

Submitted 13 November 2007; revised version accepted 10 June 2008.
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