Legat Franz J
Department of Dermatology and Venerology, Medical University of Graz, Graz, Austria.
Front Med (Lausanne). 2018 Nov 30;5:333. doi: 10.3389/fmed.2018.00333. eCollection 2018.
Phototherapy is widely used to treat inflammatory skin diseases such as psoriasis and atopic dermatitis. Repeated suberythemogenic doses of UV-light reduce inflammation in these diseases and ultimately may lead to a complete disappearance of cutaneous symptoms for weeks or months. Chronic pruritus is an important and highly distressing symptom of many of these inflammatory skin diseases. Interestingly, pruritus is also reduced or completely abolished by UV-treatment of psoriasis and atopic dermatitis, and sometimes reduction of pruritus is the first indication for skin improvement by phototherapy. The cutaneous nervous system is an integral part of skin anatomy, and free nerve endings of sensory cutaneous nerve fibers reach up into the epidermis getting in close contact with epidermal cells and mediators from epidermal cells released into the intercellular space. Stimulation of "pruriceptors" within this group of sensory nerve fibers generates a neuronal signal eventually transmitted via the dorsal root and the spinal cord to the brain, where it is recognized as "itch". UV-light may directly affect cutaneous sensory nerve fibers or, via the release of mediators from cells within the skin, indirectly modulate their function as well as the transmission of itch to the central nervous system inducing the clinically recognized antipruritic effect of phototherapy.
光疗被广泛用于治疗炎症性皮肤病，如银屑病和特应性皮炎。重复给予亚红斑量的紫外线可减轻这些疾病的炎症，最终可能导致皮肤症状在数周或数月内完全消失。慢性瘙痒是许多这类炎症性皮肤病的一个重要且极其困扰患者的症状。有趣的是，银屑病和特应性皮炎经紫外线治疗后，瘙痒也会减轻或完全消除，有时瘙痒减轻是光疗使皮肤改善的首个迹象。皮肤神经系统是皮肤解剖结构的一个组成部分，感觉性皮肤神经纤维的游离神经末梢向上延伸至表皮，与表皮细胞以及释放到细胞间空间的表皮细胞介质密切接触。刺激这组感觉神经纤维内的“瘙痒感受器”会产生一个神经元信号，最终通过背根和脊髓传递到大脑，在大脑中被识别为“瘙痒”。紫外线可能直接影响皮肤感觉神经纤维，或者通过皮肤内细胞释放介质，间接调节其功能以及瘙痒向中枢神经系统的传递，从而产生临床上公认的光疗止痒效果。
