Benefits of controlled ultraviolet radiation in the treatment of dermatological diseases.

Phototherapy is a second-line treatment modality for the most common dermatoses that is safe and effective. Most phototherapy regimens denote the use of ultraviolet (UV) radiation of different wavelengths in the management of several dermatoses. Currently, irradiations with broadband UVB (290-320 nm), narrowband UVB (311-313 nm), 308 nm excimer laser, UVA 1 (340-400 nm), UVA with psoralen (PUVA), and extracorporeal photochemotherapy (photopheresis) are being used. Beneficial effects of UV radiation are far from being completely understood. Dermatoses that may benefit from such approach are numerous, with psoriasis, parapsoriasis, atopic dermatitis, cutaneous T-cell lymphomas, morphea, and vitiligo vulgaris as main indications. UVB radiation primarily acts on cells at the epidermis and the epidermodermal junction, while UVA radiation affects epidermal and dermal components, especially blood vessels. UVradiation has im- mediate and delayed effects. Immediate effects are the formation of DNA photoproducts and DNA damage leading to apoptosis of heratinocytes, Langerhans cells, activated T-lymphocytes, neutrophils, macrophages, NK cells, fibroblasts, endothelial cells, and mast-cells, cell membrane damage by lipid peroxidation, and isomerization of chromophores such as urocanic acid. Delayed effects include synthesis of prostaglandins and cytokines that play important roles in immune suppression. Systemic and local immune suppression, alteration in cytokine expression (induction of interleukin-1 (IL-1) receptor antagonist, decrease in IL-2, increase in IL-IO, IL-15), and cell cycle arrest may all contribute to the suppression of disease activity. PUVA is a form of controlled and repeated induction of phototoxic reactions which uses UVA light to activate chemicals known as psoralens. The conjunction of psoralens with epidermal DNA inhibits DNA synthesis and causes cell apoptosis. PUVA also causes an alteration in the expression of cytokines and cytokine receptors. Psoralens interact with RNA, proteins and other cellular components and indirectly modify proteins and lipids via singlet oxygen-mediated reactions or by generating of free radicals. Psoralens and UV radiation also stimulate melanogenesis with variable effects in patients with vitiligo vulgaris. Extracorporealphotopheresis is treatment modality used in management of erythrodermic cutaneous T-cell lymphomas. It is very potent in induction of lymphocyte apoptosis. Despite the introduction of numerous potent bioengineered systemic medications in the field of dermatology, phototherapy remains established, and often preferred, option for the most common dermatoses.