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Dynamic mechanical allodynia: A homogeneous entity?
Scandinavian Journal of Pain 2 (2011) 83–84
Contents lists available at ScienceDirect
Scandinavian Journal of Pain journal homepage: www.ScandinavianJournalPain.com
Editorial comment
Dynamic mechanical allodynia: A homogeneous entity? Nanna Brix Finnerup ∗ Danish Pain Research Center, Aarhus University Hospital, Noerrebrogade 44, Building 1A, DK-8000 Aarhus, Denmark
One intriguing symptom of neuropathic pain is dynamic mechanical allodynia. It is established that dynamic mechanical allodynia in the periphery is mediated by large afferent fibers [1], but despite different theories the exact underlying mechanisms of dynamic mechanical allodynia are still unknown. Capsaicin, the active ingredient in hot chilli pepper, activates a subpopulation of the transient receptor potential vanilloid (TRPV1) receptors, which are located on small- and medium-sized nociceptors. This causes ongoing burning pain, a flare response, hypoesthesia to cold, and a secondary hyperalgesic area with heat and pinprick hyperalgesia and dynamic mechanical allodynia [2,3]. These symptoms are similar to what is seen following heat injury [4], and experimental injection or topical application of capsaicin may thus be a model of a burn injury. Due to the development of allodynia and hyperalgesia, the capsaicin model has also been used to study clinical expressions of neuropathic pain [2]. In order to study the usefulness of the capsaicin model in reflecting the dynamic mechanical allodynia seen in neuropathic pain patients, Samuelsson et al. in this issue of the Scandinavian Journal of Pain compared the psychophysical characteristics of dynamic mechanical allodynia in the area of neuropathic pain and in the secondary hyperalgesic area in capsaicin-treated skin [5]. Dynamic mechanical allodynia was examined in the area of neuropathic pain in nine patients with well-characterized pain due to a peripheral nerve or nerve root lesion, and subsequently in the area of the secondary hyperalgesia following intradermal capsaicin injection on the contralateral side. There were no obvious
differences between dynamic mechanical allodynia caused by a nerve lesion or capsaicin; patients used the same descriptors, the evoked pain was independent of the width of the stimulation brush, and an increased number of strokes increased the total pain experience (integrated intensity and time) on both sides. The total pain intensity and the duration of after sensations were, however, higher in the area of painful neuropathy compared with the capsaicin-induced secondary hyperalgesic area. This result is a very important step for future studies because it suggests that dynamic mechanical allodynia following capsaicin injection and nerve injury are perceptually similar phenomena. We cannot, however, conclude that the underlying mechanisms for dynamic mechanical allodynia in these and other conditions are similar (Fig. 1). The study also included an examination of dynamic mechanical allodynia in the secondary hyperalgesic area in nine healthy subjects. In contrast to the contralateral healthy side in patients, only few healthy subjects developed secondary hyperalgesia. Whether this is due to predisposed genetic factors, psychological factors, the fact that patients had the examination done in the neuropathic pain area first, or a spread of central hyperexcitability to the contralateral side is unknown, but it is an interesting finding that deserves to be studied further. We do not know the exact underlying mechanisms of dynamic mechanical allodynia, which may be a devastating symptom in some neuropathic pain patients, but the study by Samuelsson et al. [5] brings us a small step further to the understanding of this peculiar symptom.
DOI of refers to article:10.1016/j.sjpain.2011.01.003. ∗ Tel.: +45 8949 3455; fax: +45 8949 3269. E-mail address: fi[email protected] 1877-8860/$ – see front matter © 2011 Scandinavian Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sjpain.2011.02.004
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N.B. Finnerup / Scandinavian Journal of Pain 2 (2011) 83–84
Fig. 1. Dynamic mechanical allodynia in different conditions. Various conditions can, via the same or different mechanisms, cause dynamic mechanical allodynia (DMA), which may be a single entity or different entities with various presentations.
References [1] Landerholm AH, Hansson PT. Mechanisms of dynamic mechanical allodynia and dysesthesia in patients with peripheral and central neuropathic pain. Eur J Pain 2010 [Epub November 19]. [2] Klein T, Magerl W, Rolke R, Treede RD. Human surrogate models of neuropathic pain. Pain 2003;115:227–33.
[3] Callsen MG, Moller AT, Sorensen K, Jensen TS, Finnerup NB. Cold hyposensitivity after topical application of capsaicin in humans. Exp Brain Res 2008;191:447–52. [4] Yucel A, Miyazawa A, Andersen OK, Arendt-Nielsen L. Comparison of hyperalgesia induced by capsaicin injection and controlled heat injury: effect on temporal summation. Somatosens Mot Res 2004;21:15–24. [5] Samuelsson M, Leffler A-S, Hansson P. Dynamic mechanical allodynia in the secondary hyperalgesic area in the capsaicin model – perceptually similar phenomena as in painful neuropathy? Scand J Pain 2011;2:85–92.
Contents lists available at ScienceDirect
Scandinavian Journal of Pain journal homepage: www.ScandinavianJournalPain.com
Editorial comment
Dynamic mechanical allodynia: A homogeneous entity? Nanna Brix Finnerup ∗ Danish Pain Research Center, Aarhus University Hospital, Noerrebrogade 44, Building 1A, DK-8000 Aarhus, Denmark
One intriguing symptom of neuropathic pain is dynamic mechanical allodynia. It is established that dynamic mechanical allodynia in the periphery is mediated by large afferent fibers [1], but despite different theories the exact underlying mechanisms of dynamic mechanical allodynia are still unknown. Capsaicin, the active ingredient in hot chilli pepper, activates a subpopulation of the transient receptor potential vanilloid (TRPV1) receptors, which are located on small- and medium-sized nociceptors. This causes ongoing burning pain, a flare response, hypoesthesia to cold, and a secondary hyperalgesic area with heat and pinprick hyperalgesia and dynamic mechanical allodynia [2,3]. These symptoms are similar to what is seen following heat injury [4], and experimental injection or topical application of capsaicin may thus be a model of a burn injury. Due to the development of allodynia and hyperalgesia, the capsaicin model has also been used to study clinical expressions of neuropathic pain [2]. In order to study the usefulness of the capsaicin model in reflecting the dynamic mechanical allodynia seen in neuropathic pain patients, Samuelsson et al. in this issue of the Scandinavian Journal of Pain compared the psychophysical characteristics of dynamic mechanical allodynia in the area of neuropathic pain and in the secondary hyperalgesic area in capsaicin-treated skin [5]. Dynamic mechanical allodynia was examined in the area of neuropathic pain in nine patients with well-characterized pain due to a peripheral nerve or nerve root lesion, and subsequently in the area of the secondary hyperalgesia following intradermal capsaicin injection on the contralateral side. There were no obvious
differences between dynamic mechanical allodynia caused by a nerve lesion or capsaicin; patients used the same descriptors, the evoked pain was independent of the width of the stimulation brush, and an increased number of strokes increased the total pain experience (integrated intensity and time) on both sides. The total pain intensity and the duration of after sensations were, however, higher in the area of painful neuropathy compared with the capsaicin-induced secondary hyperalgesic area. This result is a very important step for future studies because it suggests that dynamic mechanical allodynia following capsaicin injection and nerve injury are perceptually similar phenomena. We cannot, however, conclude that the underlying mechanisms for dynamic mechanical allodynia in these and other conditions are similar (Fig. 1). The study also included an examination of dynamic mechanical allodynia in the secondary hyperalgesic area in nine healthy subjects. In contrast to the contralateral healthy side in patients, only few healthy subjects developed secondary hyperalgesia. Whether this is due to predisposed genetic factors, psychological factors, the fact that patients had the examination done in the neuropathic pain area first, or a spread of central hyperexcitability to the contralateral side is unknown, but it is an interesting finding that deserves to be studied further. We do not know the exact underlying mechanisms of dynamic mechanical allodynia, which may be a devastating symptom in some neuropathic pain patients, but the study by Samuelsson et al. [5] brings us a small step further to the understanding of this peculiar symptom.
DOI of refers to article:10.1016/j.sjpain.2011.01.003. ∗ Tel.: +45 8949 3455; fax: +45 8949 3269. E-mail address: fi[email protected] 1877-8860/$ – see front matter © 2011 Scandinavian Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sjpain.2011.02.004
84
N.B. Finnerup / Scandinavian Journal of Pain 2 (2011) 83–84
Fig. 1. Dynamic mechanical allodynia in different conditions. Various conditions can, via the same or different mechanisms, cause dynamic mechanical allodynia (DMA), which may be a single entity or different entities with various presentations.
References [1] Landerholm AH, Hansson PT. Mechanisms of dynamic mechanical allodynia and dysesthesia in patients with peripheral and central neuropathic pain. Eur J Pain 2010 [Epub November 19]. [2] Klein T, Magerl W, Rolke R, Treede RD. Human surrogate models of neuropathic pain. Pain 2003;115:227–33.
[3] Callsen MG, Moller AT, Sorensen K, Jensen TS, Finnerup NB. Cold hyposensitivity after topical application of capsaicin in humans. Exp Brain Res 2008;191:447–52. [4] Yucel A, Miyazawa A, Andersen OK, Arendt-Nielsen L. Comparison of hyperalgesia induced by capsaicin injection and controlled heat injury: effect on temporal summation. Somatosens Mot Res 2004;21:15–24. [5] Samuelsson M, Leffler A-S, Hansson P. Dynamic mechanical allodynia in the secondary hyperalgesic area in the capsaicin model – perceptually similar phenomena as in painful neuropathy? Scand J Pain 2011;2:85–92.