瘙痒评估

瘙痒被定义为一种令人不快、引起搔抓欲望的感觉。英文中 pruritus 和 itch 为可互相换用的同义词。瘙痒为皮肤科最常见的主观症状，可伴或不伴有可见皮损。瘙痒可为局部或全身性。

鉴别急性瘙痒和慢性瘙痒非常重要。 瘙痒持续时间超过6周即为慢性瘙痒。[1]Ständer S, Weisshaar E, Mettang T, et al. Clinical classification of itch: a position paper of the International Forum for the Study of Itch. Acta Derm Venereol. 2007;87:291-294. http://www.ncbi.nlm.nih.gov/pubmed/17598029?tool=bestpractice.com 根据病因，慢性瘙痒可分为皮肤病性的、全身性的、神经原性的、心因性/身心性、混合原因导致的及病因不明的。 慢性瘙痒可令人非常苦恼，并对治疗抵抗。 慢性瘙痒程度常与生活质量受损程度、耻辱感、抑郁严重程度及情绪压力相关。

依据目前普遍接受的临床分类，患者的瘙痒被描述为：主要见于病变、发炎皮肤的瘙痒；主要见于未发炎正常皮肤的瘙痒；以及皮肤瘙痒伴有慢性继发性搔抓性皮损。[1]Ständer S, Weisshaar E, Mettang T, et al. Clinical classification of itch: a position paper of the International Forum for the Study of Itch. Acta Derm Venereol. 2007;87:291-294. http://www.ncbi.nlm.nih.gov/pubmed/17598029?tool=bestpractice.com

流行病学

瘙痒是一种常见的小病。德国一项纳入 11,730 名个体的大规模流行病学研究报告称，慢性瘙痒（资料收集前至少 6 周）的时点患病率为 16.8%；患病率随年龄增长而升高，16-30 岁为 12.3%，61-70 岁为 20.3%。[2]Ständer S, Schäfer I, Phan NQ, et al. Prevalence of chronic pruritus in Germany: results of a cross-sectional study in a sample working population of 11,730. Dermatology. 2010;221:229-235. http://www.ncbi.nlm.nih.gov/pubmed/20924157?tool=bestpractice.com 在挪威进行的一项自行报告病率研究中，瘙痒是最常提到的皮肤症状（7%）；东亚男性、中东/北非男性的瘙痒报告率显著更高，前者为 18%，后者为 13%。[3]Dalgard F, Holm JO, Svensson A, et al. Self reported skin morbidity and ethnicity: a population-based study in a Western community. BMC Dermatol. 2007;7:4. http://bmcdermatol.biomedcentral.com/articles/10.1186/1471-5945-7-4 http://www.ncbi.nlm.nih.gov/pubmed/17603893?tool=bestpractice.com 报告瘙痒的患者较为年轻，主要为女性，且更为苦恼；这些患者收入较低、更缺乏社会支持、负面生活事件经历较多。[4]Dalgard F, Lien L, Dalen I. Itch in the community: associations with psychosocial factors among adults. J Eur Acad Dermatol Venereol. 2007;21:1215-1219. http://www.ncbi.nlm.nih.gov/pubmed/17894708?tool=bestpractice.com

瘙痒为许多皮肤疾病的常见症状。 比如，瘙痒是特应性湿疹的主要症状，所有患者在其疾病过程中都曾有不同程度瘙痒。[5]Ständer S, Streit M, Darsow U, et al. Diagnostic and therapeutic procedures in chronic pruritus [in German]. J Dtsch Dermatol Ges. 2006;4:350-370. http://www.ncbi.nlm.nih.gov/pubmed/16638066?tool=bestpractice.com 与此类似，大约70%到90%银屑病患者有瘙痒症状。[6]Gupta MA, Gupta AK, Kirkby S, et al. Pruritus in psoriasis. A prospective study of some psychiatric and dermatologic correlates. Arch Dermatol. 1988;124:1052-1057. http://www.ncbi.nlm.nih.gov/pubmed/3389849?tool=bestpractice.com [7]Yosipovitch G, Goon A, Wee J, et al. The prevalence and clinical characteristics of pruritus among patients with extensive psoriasis. Br J Dermatol. 2000;143:969-973. http://www.ncbi.nlm.nih.gov/pubmed/11069504?tool=bestpractice.com [8]Szepietowski JC, Reich A, Wisnicka B. Itching in patients suffering from psoriasis. Acta Dermatovenerol Croat. 2002;10:221-226. http://www.ncbi.nlm.nih.gov/pubmed/12588672?tool=bestpractice.com [9]Szepietowski JC, Reich A. Pruritus in psoriasis: an update. Eur J Pain. 2016;20:41-46. http://www.ncbi.nlm.nih.gov/pubmed/26415584?tool=bestpractice.com 瘙痒也可能并发于其他全身性疾病，例如慢性肾衰竭、血液系统恶性肿瘤或肝脏疾病。[10]Manenti L, Tansinda P, Vaglio A. Uraemic pruritus: clinical characteristics, pathophysiology and treatment. Drugs. 2009;69:251-263. http://www.ncbi.nlm.nih.gov/pubmed/19275270?tool=bestpractice.com 例如，据估计，血液透析患者的慢性瘙痒发生率为 25%-55%。[11]Weiss M, Mettang T, Tschulena U, et al. Prevalence of chronic itch and associated factors in haemodialysis patients: a representative cross-sectional study. Acta Derm Venereol. 2015;95:816-821. http://www.medicaljournals.se/acta/content/?doi=10.2340/00015555-2087&html=1 http://www.ncbi.nlm.nih.gov/pubmed/25740325?tool=bestpractice.com [12]Szepietowski JC, Sikora M, Kusztal M, et al. Uremic pruritus: a clinical study of maintenance hemodialysis patients. J Dermatol. 2002;29:621-627. http://www.ncbi.nlm.nih.gov/pubmed/12432992?tool=bestpractice.com [13]Hu X, Sang Y, Yang M, et al. Prevalence of chronic kidney disease-associated pruritus among adult dialysis patients: A meta-analysis of cross-sectional studies. Medicine (Baltimore). 2018 May;97(21):e10633. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6392722 http://www.ncbi.nlm.nih.gov/pubmed/29794739?tool=bestpractice.com

病理生理学

病理生理机制取决于基础疾病。许多不同的介质可诱发或调节瘙痒，包括组胺、乙酰胆碱、儿茶酚胺、血液激肽、趋化因子、细胞因子（白介素 2、白介素 31）、神经肽、内皮素、内辣椒素、内源性大麻素、下丘脑-垂体轴激素、激肽释放酶、蛋白酶、前列腺素、白三烯 B4、神经营养肽及阿片类物质。[14]Paus R, Schmelz M, Biro T, et al. Frontiers in pruritus research: scratching the brain for more effective itch therapy. J Clin Invest. 2006;116:1174-1186. http://www.jci.org/articles/view/28553 http://www.ncbi.nlm.nih.gov/pubmed/16670758?tool=bestpractice.com

瘙痒的特定神经元通路已明确。 瘙痒刺激主要由机械不敏感的无髓鞘C传入神经纤维传导，该纤维传导速度特别慢、神经支配面积大、经皮电阈值高。

在脊髓，瘙痒刺激由脊髓背角的特定瘙痒接受神经元传导至丘脑腹内侧核后部，后者投射至背侧岛叶皮质。已经明确脊髓内表达胃泌素释放肽受体的瘙痒通路神经元。[15]Sun YG, Zhao ZQ, Meng XL, et al. Cellular basis of itch sensation. Science. 2009;325:1531-1534. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2786498 http://www.ncbi.nlm.nih.gov/pubmed/19661382?tool=bestpractice.com [16]Akiyama T, Tominaga M, Takamori K, et al. Roles of glutamate, substance P, and gastrin-releasing peptide as spinal neurotransmitters of histaminergic and nonhistaminergic itch. Pain. 2014;155:80-92. http://www.ncbi.nlm.nih.gov/pubmed/24041961?tool=bestpractice.com [17]Papoiu AD, Coghill RC, Kraft RA, et al. A tale of two itches. Common features and notable differences in brain activation evoked by cowhage and histamine induced itch. Neuroimage. 2012;59:3611-3623. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3288667 http://www.ncbi.nlm.nih.gov/pubmed/22100770?tool=bestpractice.com 诱发的瘙痒刺激同时激活前扣带皮层、辅助运动区及主要位于左半球的下顶叶。

随着瘙痒感的产生，大脑内多个活化的区域对单一瘙痒中心作出应对，反应出瘙痒的多维性。[18]Steinhoff M, Bienenstock J, Schmelz M, et al. Neurophysiological, neuroimmunological, and neuroendocrine basis of pruritus. J Invest Dermatol. 2006;126:1705-1718. http://www.jidonline.org/article/S0022-202X(15)33013-X/fulltext http://www.ncbi.nlm.nih.gov/pubmed/16845410?tool=bestpractice.com 重要的是，已证实在慢性瘙痒患者中瘙痒刺激引起的脑活动与健康对照受试者所观察到的显著不同。[19]Ishiuji Y, Coghill RC, Patel TS, et al. Distinct patterns of brain activity evoked by histamine-induced itch reveal an association with itch intensity and disease severity in atopic dermatitis. Br J Dermatol. 2009;161:1072-1080. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2784001 http://www.ncbi.nlm.nih.gov/pubmed/19663870?tool=bestpractice.com