The main wavelengths used for phototherapy include broadband ultraviolet B (BB-UVB), narrowband UVB (NB-UVB), ultraviolet A (UVA) 1, and UVA for psoralen photochemotherapy (PUVA); these have different depths of penetration and interact with a specific range of molecules rendering unique photobiologic properties with respect to potency, side effects, and diseases in which they are effective.
Targeted therapy devices can deliver distinct wavelengths of ultraviolet radiation to only lesional skin. Such devices that can deliver wavelengths of UVR at or close to those that are most effective at clearing localized atopic dermatitis, psoriasis, vitiligo, and cutaneous T-cell lymphoma have been evaluated, and are being used clinically.
Sunburn-like reactions are the most common short term adverse effect of phototherapy. UVB phototoxicity usually peaks at 12 to 24 hours and PUVA reaction manifests at 24 to 48 or even 72 hours. Importantly, except for PUVA therapy for which formal long term follow up studies established an increased risk of lentigines, squamous cell carcinoma, and possibly melanoma, other forms of phototherapy appear to be remarkably safe.
MECHANISMS OF PHOTOTHERAPY
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 biologic effects. The expanded use of phototherapy for dermatologic and nondermatologic conditions can be attributed to the following factors: identification of photosensitizers with unique photochemical properties; development of novel methods for the delivery of light to cutaneous and noncutaneous surfaces; and manufacture of light sources that emit selective wavelengths of radiant energy. The main phototherapeutic devices that are in use today (aside from lasers, high-output incoherent light sources, and visible light sources employed for photodynamic therapy) include broadband ultraviolet B (BB-UVB), narrowband UVB (NB-UVB), ultraviolet A (UVA) 1, and UVA for psoralen photochemotherapy (PUVA). Ideally, these devices used for therapeutic ultraviolet radiation (UVR) should be safe, efficient, and cost-effective. Therefore, understanding the basic principles of these devices is important for dermatologists and other providers using phototherapy for the management of dermatologic diseases.1,2
The distinct wavelengths of UVR used for phototherapy have different depths of penetration and interact with a specific range of molecules. As a consequence, each form of phototherapy has unique photochemical and photobiologic properties with respect to potency, side effects, and diseases in which they are effective (Fig. 198-1).
Summary of effects from ultraviolet A (UVA), psoralen and ultraviolet A (PUVA), or ultraviolet B (UVB) treatment. Detailed discussion in text. Boxes in purple indicate effects of either UVA and/or PUVA only, boxes in green indicate effects of both UVB and UVA and/or PUVA. The bottom two rows of boxes indicate clinical relevance of ...