Phototherapy at a Glance
- Phototherapeutic devices have varying properties with respect to depth of UV penetration into the skin, effects on cells and molecules, potency, side effects and diseases in which they are most effective.
- In use today are narrowband and broadband UVB, UVA as part of psoralen photochemotherapy (PUVA), UVA1 and targeted phototherapy (excimer lasers and nonlaser monochromatic excimer light sources).
- Narrowband UVB is currently preferred to treat psoriasis, other inflammatory skin diseases, and vitiligo.
- Psoralen-UVA photochemotherapy (PUVA) combines oral or topical psoralen compounds with UVA light sources. Its main uses are treatment of cutaneous T-cell lymphoma, vitiligo, and psoriasis that is resistant to narrowband UVB.
- UVA1 phototherapy is particularly effective for sclerotic skin diseases such as localized scleroderma, acute flares of atopic dermatitis and urticaria pigmentosa.
- Targeted phototherapy allowing relatively high UV doses to be delivered to diseased skin while sparing normal skin.
Diseases amenable to phototherapy include psoriasis, atopic dermatitis, cutaneous T-cell lymphoma, vitiligo, localized and systemic scleroderma, pruritus, photodermatoses, lichen planus, pityriasis lichenoides, urticaria pigmentosa and granuloma annulare.
Phototherapy is the use of ultraviolet radiation or visible light for therapeutic purposes. Its beneficial effects in vitiligo were first recognized thousands of years ago in India and Egypt, and its activity is now well established for a variety of other dermatologic conditions. The enduring appeal of phototherapy is based on its relative safety coupled with an ongoing interest in its molecular and biological effects. The manufacture of light sources that emit selective wavelengths of radiant energy, identification of photosensitizers with unique photochemical properties, and the development of novel methods for the delivery of light to cutaneous and noncutaneous surfaces have all contributed to its expanded use for dermatologic and nondermatologic conditions. Aside from lasers, high output incoherent light sources, and visible light sources employed for photodynamic therapy, the main phototherapic devices that are in use today are broadband UVB (BB-UVB), narrowband UVB (NB-UVB), UVA1, and UVA for psoralen photochemotherapy (PUVA). Ideally, devices used for therapeutic ultraviolet radiation (UVR) should do so in a safe, efficient and cost-effective manner. Understanding the basic principles of these devices is important for dermatologists and other providers utilizing phototherapy for the management of dermatologic diseases.1–2
The different wavelengths of ultraviolet radiation used for phototherapy each have distinct photochemical and photobiologic properties, which include differences in depth of penetration and the range of molecules in the skin with which they interact. As a consequence, each form of phototherapy has unique properties with respect to potency, side effects, and diseases in which they are effective.
Most UVB radiation (290–320 nm) is absorbed by the epidermis and superficial dermis.3 This form of radiant energy produces many different types of DNA damage4; however, pyrimidine dimers and 6,4 pyrimidine-pyrimidone photoproducts are thought to be particularly important for both its efficacy and its toxicity. UVB also causes photochemical changes in trans-urocanic acid, converting ...