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＞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
[2]Millington GWM, Collins A, Lovell CR, et al. British Association of Dermatologists' guidelines for the investigation and management of generalized pruritus in adults without an underlying dermatosis, 2018. Br J Dermatol. 2018 Jan;178(1):34-60.
https://academic.oup.com/bjd/article/178/1/34/6668398?login=false
http://www.ncbi.nlm.nih.gov/pubmed/29357600?tool=bestpractice.com
[3]Ständer S, Zeidler C, Augustin M, et al. S2k guideline: diagnosis and treatment of chronic pruritus. J Dtsch Dermatol Ges. 2022 Oct;20(10):1387-402.
https://onlinelibrary.wiley.com/doi/10.1111/ddg.14830
http://www.ncbi.nlm.nih.gov/pubmed/36252071?tool=bestpractice.com
根据病因，慢性瘙痒可分为皮肤病性、全身性、神经原性、心因性/身心性、混合原因所致以及病因不明的瘙痒。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
瘙痒是一种常见疾病。欧洲人群研究报告称，瘙痒患病率（急性和/或慢性 [持续＞6 周]）为 7%-17%。[4]Dalgard F, Svensson A, Holm JØ, et al. Self-reported skin morbidity in Oslo. Associations with sociodemographic factors among adults in a cross-sectional study. Br J Dermatol. 2004 Aug;151(2):452-7.
http://www.ncbi.nlm.nih.gov/pubmed/15327554?tool=bestpractice.com
[5]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(3):229-35.
http://www.ncbi.nlm.nih.gov/pubmed/20924157?tool=bestpractice.com
[6]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 Jun 29;7:4.
http://bmcdermatol.biomedcentral.com/articles/10.1186/1471-5945-7-4
http://www.ncbi.nlm.nih.gov/pubmed/17603893?tool=bestpractice.com
患病率随年龄增长而增加。一项系统评价和荟萃分析报告称，老年人（≥60 岁）的瘙痒总体患病率为 21%。[7]Chen S, Zhou F, Xiong Y. Prevalence and risk factors of senile pruritus: a systematic review and meta-analysis. BMJ Open. 2022 Feb 24;12(2):e051694.
https://bmjopen.bmj.com/content/12/2/e051694.long
http://www.ncbi.nlm.nih.gov/pubmed/35210338?tool=bestpractice.com
在德国进行的一项大型流行病学研究发现，年轻人（16-30 岁）的发病率为 12.3%，而在 61-70 岁人群中上升至 20.3%。[5]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(3):229-35.
http://www.ncbi.nlm.nih.gov/pubmed/20924157?tool=bestpractice.com
在挪威进行的一项自报发病率研究中，瘙痒是最常被提及的皮肤症状（7%）。[4]Dalgard F, Svensson A, Holm JØ, et al. Self-reported skin morbidity in Oslo. Associations with sociodemographic factors among adults in a cross-sectional study. Br J Dermatol. 2004 Aug;151(2):452-7.
http://www.ncbi.nlm.nih.gov/pubmed/15327554?tool=bestpractice.com
[6]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 Jun 29;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。[8]Dalgard F, Lien L, Dalen I. Itch in the community: associations with psychosocial factors among adults. J Eur Acad Dermatol Venereol. 2007 Oct;21(9):1215-9.
http://www.ncbi.nlm.nih.gov/pubmed/17894708?tool=bestpractice.com
东亚男性、中东/北非男性的瘙痒报告率显著更高，分别为 18% 和 13%。[6]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 Jun 29;7:4.
http://bmcdermatol.biomedcentral.com/articles/10.1186/1471-5945-7-4
http://www.ncbi.nlm.nih.gov/pubmed/17603893?tool=bestpractice.com
瘙痒为许多皮肤疾病的常见症状。[2]Millington GWM, Collins A, Lovell CR, et al. British Association of Dermatologists' guidelines for the investigation and management of generalized pruritus in adults without an underlying dermatosis, 2018. Br J Dermatol. 2018 Jan;178(1):34-60.
https://academic.oup.com/bjd/article/178/1/34/6668398?login=false
http://www.ncbi.nlm.nih.gov/pubmed/29357600?tool=bestpractice.com
[9]Satoh T, Yokozeki H, Murota H, et al. 2020 guidelines for the diagnosis and treatment of cutaneous pruritus. J Dermatol. 2021 Sep;48(9):e399-413.
https://onlinelibrary.wiley.com/doi/10.1111/1346-8138.16066
http://www.ncbi.nlm.nih.gov/pubmed/34288036?tool=bestpractice.com
例如，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。[10]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%-90% 的银屑病患者有瘙痒症状。[11]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
[12]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
[13]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
[14]Jaworecka K, Kwiatkowska D, Marek-Józefowicz L, et al. Characteristics of pruritus in various clinical variants of psoriasis: final report of the binational, multicentre, cross-sectional study. J Eur Acad Dermatol Venereol. 2023 Apr;37(4):787-95.
http://www.ncbi.nlm.nih.gov/pubmed/36606568?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。[15]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%。[16]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
[17]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
[18]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。[19]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。[20]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
[21]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
[22]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，反映出瘙痒的多维性。[23]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。[24]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
