Laboratory for Experimental Cutaneous Pain Research, SMI®, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
Department of Dermatology and Allergy, Herlev and Gentofte Hospital, Copenhagen University Hospital, Copenhagen, Denmark.
Br J Dermatol. 2017 Jul;177(1):107-116. doi: 10.1111/bjd.15335. Epub 2017 Jun 9.
Chronic itch is difficult to treat. Low-concentration topical capsaicin (0·006-0·05%) has previously been applied in itch therapy but evidence on its efficacy is contradictory.
This vehicle-controlled, double-blinded study investigated the effect of topical capsaicin 8% after 1- and 24-h application on evoked itch, neurogenic inflammation and itch-associated dysaesthesia.
Sixteen healthy volunteers (aged 22 ± 0·5 years, nine female) were treated with capsaicin for 1 h and 24 h, and vehicle for 24 h on each volar forearm. Subsequently, histamine (1%, administered prick test lancets) and cowhage (40-45 spicules) were applied to the pretreated areas. Evoked itch and pain intensities were recorded for 10 min using a visual analogue scale (0-10 cm), while sensitivity to touch-evoked itch was evaluated using von Frey filaments before and after itch provocations. Neurogenic inflammation was assessed using perfusion imaging.
In the vehicle areas peak itch responses to histamine and cowhage were 4·67 ± 0·58 and 5·15 ± 0·71, respectively. Capsaicin pretreatment reduced peak itch responses to histamine and cowhage after 24-h pretreatment to 1·41 ± 0·58 (P = 0·003) and 0·81 ± 0·18, (P < 0·001), respectively. Capsaicin pretreatment for 1 h reduced only cowhage-induced itch (P = 0·023). Furthermore, 24-h capsaicin pretreatment abolished punctuate hyperknesis and lowered histamine-induced neurogenic inflammation but did not affect weal reactions.
Topical capsaicin 8% pretreatment for 24 h reduced histaminergic and nonhistaminergic itch by about 75%, while a significant reduction (≈60%) was achieved for only nonhistaminergic itch in a standard 1-h treatment. Further investigations are needed to elucidate the clinical potential of high-concentration capsaicin as an antipruritic.
慢性瘙痒难以治疗。低浓度的局部辣椒素（0.006-0.05%）曾用于瘙痒治疗，但疗效证据存在矛盾。
本项对照、双盲研究旨在探讨 1 小时和 24 小时应用 8%局部辣椒素对诱发性瘙痒、神经源性炎症和瘙痒相关感觉异常的影响。
16 名健康志愿者（年龄 22 ± 0.5 岁，9 名女性）在每只前臂的掌侧接受辣椒素治疗 1 小时和 24 小时，以及载体治疗 24 小时。随后，用盐酸（1%，用针刺试验 lancets 给药）和毛毡苔（40-45 个刺）在预处理区域给药。用视觉模拟量表（0-10cm）记录 10 分钟的诱发性瘙痒和疼痛强度，而在瘙痒诱发前后，用 von Frey 细丝评估触发性瘙痒的敏感性。使用灌注成像评估神经源性炎症。
在载体区域，组胺和毛毡苔引起的瘙痒峰值反应分别为 4.67 ± 0.58 和 5.15 ± 0.71。辣椒素预处理可使 24 小时预处理后组胺和毛毡苔引起的瘙痒峰值反应分别降低至 1.41 ± 0.58（P = 0.003）和 0.81 ± 0.18（P < 0.001）。辣椒素预处理 1 小时仅降低毛毡苔引起的瘙痒（P = 0.023）。此外，24 小时辣椒素预处理可消除点状 hyperknesis，并降低组胺引起的神经源性炎症，但不影响风团反应。
24 小时外用 8%辣椒素预处理可使组胺能和非组胺能瘙痒减少约 75%，而标准的 1 小时治疗仅可使非组胺能瘙痒显著减少（约 60%）。需要进一步研究以阐明高浓度辣椒素作为止痒剂的临床潜力。
