Dynamic mechanical allodynia: A homogeneous entity?

Abstract

One intriguing symptom of neuropathic pain is dynamic echanical allodynia. It is established that dynamic mechancal allodynia in the periphery is mediated by large afferent bers [1], but despite different theories the exact underlyng mechanisms of dynamic mechanical allodynia are still nknown. Capsaicin, the active ingredient in hot chilli pepper, actiates a subpopulation of the transient receptor potential vanilloid TRPV1) receptors, which are located on smalland medium-sized ociceptors. This causes ongoing burning pain, a flare response, ypoesthesia to cold, and a secondary hyperalgesic area with eat and pinprick hyperalgesia and dynamic mechanical allodyia [2,3]. These symptoms are similar to what is seen following eat injury [4], and experimental injection or topical application f capsaicin may thus be a model of a burn injury. Due to the evelopment of allodynia and hyperalgesia, the capsaicin model as also been used to study clinical expressions of neuropathic pain 2]. In order to study the usefulness of the capsaicin model in eflecting the dynamic mechanical allodynia seen in neuropathic ain patients, Samuelsson et al. in this issue of the Scandinavian ournal of Pain compared the psychophysical characteristics of ynamic mechanical allodynia in the area of neuropathic pain and n the secondary hyperalgesic area in capsaicin-treated skin [5]. ynamic mechanical allodynia was examined in the area of neuopathic pain in nine patients with well-characterized pain due o a peripheral nerve or nerve root lesion, and subsequently in he area of the secondary hyperalgesia following intradermal capaicin injection on the contralateral side. There were no obvious