Greaves Malcolm W, Khalifa Nedha
St. Johns Institute of Dermatology, St. Thomas' Hospital, London, UK.
Int Arch Allergy Immunol. 2004 Oct;135(2):166-72. doi: 10.1159/000080898. Epub 2004 Sep 16.
Recent research in neurophysiology of itch has indicated the existence of itch-dedicated nociceptor neurones. The perception of itch is regulated by tonically inhibitory descending neuronal pathways and nociceptor spinal neuronal circuits. There is at present no convincing evidence of an 'itch centre' in the brain. A classification of itch has been proposed, based on neurophysiological considerations, which stresses the importance of neurogenic and neuropathic itch, and assists in differential diagnosis and selection of treatment. However, more than one class of itch can occur concurrently in the same patient. The importance of cross- talk between dermal mast cells and nociceptor nerve terminals, involving cleavage of proteinase-activated receptor 2 by mast cell tryptase, is highlighted. The pruritus of cholestasis is mediated at least in part by opioid peptides synthesized by the liver, and elevated levels of these mediators are found in the plasma and skin of patients with itch due to cholestasis. The combined use of both mu-receptor antagonists and kappa-receptor agonists (anti-pruritic) is worth exploring.
近期关于瘙痒神经生理学的研究表明存在专门负责瘙痒的伤害性感受器神经元。瘙痒的感知由持续抑制性下行神经通路和伤害性感受器脊髓神经回路调节。目前尚无确凿证据表明大脑中存在“瘙痒中枢”。基于神经生理学考虑，已提出一种瘙痒分类方法，该方法强调神经源性和神经性瘙痒的重要性，并有助于鉴别诊断和治疗选择。然而，同一患者可能同时出现不止一类瘙痒。强调了真皮肥大细胞与伤害性感受器神经末梢之间相互作用的重要性，其中涉及肥大细胞类胰蛋白酶对蛋白酶激活受体2的裂解。胆汁淤积性瘙痒至少部分由肝脏合成的阿片肽介导，在胆汁淤积性瘙痒患者的血浆和皮肤中发现这些介质水平升高。μ受体拮抗剂和κ受体激动剂联合使用（止痒）值得探索。
