Stante Marcello, Hanna Dani, Lotti Torello
Department of Dermatology, University of Florence, Italy.
Dermatol Ther. 2005 Jul-Aug;18(4):308-13. doi: 10.1111/j.1529-8019.2005.00037.x.
Itch is one of the alarm sensations that human beings have phylogenetically evolved for a defense purpose. Many theories and evidences regarding the biological, pathophysiological, and clinical aspects have been given, but an update on the neuroanatomy paths and consequent treatments is required. Some chemicals that are released after skin injury and facilitate the inflammatory process can induce itch or pain or basically lead to a sensitization of the nociceptor response. In clinical practice, the present authors note a continuum of sensations from touch to pain, among which many metaesthetic sensations can be described, even if the patients themselves cannot precisely define them. The specificity of itch neurons is therefore based on their spinal connections to the itch pathway rather than on unique peripheral receptors. The ambiguity of "itch unit" discharge to pruritics and algogens may be solved by the central inhibition of itch by pain: it is common knowledge that scratching relieves itching. Conversely, centrally acting pain-inhibiting opioids enhance itch by disinhibition. The relation between itch and pain is interesting in its clinical and physiopathological aspects in order to select appropriate treatment.
瘙痒是人类在系统发育过程中为防御目的而进化出的警报感觉之一。关于生物学、病理生理学和临床方面，已经提出了许多理论和证据，但仍需要对神经解剖路径及后续治疗方法进行更新。一些在皮肤损伤后释放并促进炎症过程的化学物质可诱发瘙痒或疼痛，或基本上导致伤害感受器反应的敏化。在临床实践中，本文作者注意到从触觉到疼痛的一系列感觉，其中即使患者自己无法精确界定，也可描述出许多后感觉。因此，瘙痒神经元的特异性基于它们与瘙痒通路的脊髓连接，而非独特的外周受体。“瘙痒单位”对致痒物和致痛物放电的模糊性可能通过疼痛对瘙痒的中枢抑制来解决：众所周知，搔抓可缓解瘙痒。相反，中枢作用的止痛阿片类药物通过去抑制作用增强瘙痒。瘙痒与疼痛之间的关系在临床和生理病理方面都很有趣，以便选择合适的治疗方法。
