Photochemotherapy and Photodynamic Therapy at a Glance
- Photochemotherapy [psoralen and ultraviolet A light (PUVA)] has been successfully used for more than 30 years. Its effectiveness has profoundly influenced dermatologic therapy in general, providing treatment for a number of diverse disorders besides psoriasis and vitiligo.
- PUVA can be combined with topical treatments and with some systemic agents (retinoids, methotrexate, and, perhaps, biologics) to enhance efficacy and to reduce the number of exposures.
- The most important adverse effects of oral PUVA consist of an increased risk of squamous cell carcinoma and a possible risk of melanoma. No such increased risk was found so far with bath-PUVA.
- Extracorporeal photochemotherapy (ECP) was introduced in the 1980s for the palliative treatment of erythrodermic cutaneous T-cell lymphoma.
- ECP appears to have a major impact in the treatment of graft-versus-host disease after allogeneic bone marrow transplantation where it allows progressive reduction or even discontinuation of the concomitant immunosuppressive therapy without an increase in graft-versus-host disease activity. Several other indications are under investigation.
- No serious side effects have been reported with ECP.
- Photodynamic therapy (PDT) for skin tumors started with the introduction of topical photosensitization by a porphyrin precursor (5-aminolevulinic acid) that would avoid generalized light sensitivity over many weeks.
- Current experience with PDT of epithelial cancers and precancerous conditions suggests that actinic keratoses, Bowen disease, superficial and nodular basal cell carcinomas, and early squamous cell carcinomas can be treated curatively.
- The only significant side effect of topical PDT is a stinging pain during and shortly after irradiation. PDT has neither mutagenic nor carcinogenic potential.
Photochemotherapy with psoralens combines the use of oral or topical psoralens (P) and ultraviolet A radiation (UVA), termed PUVA. Psoralens are phototoxic compounds that enter cells and then absorb photons to produce photochemical reactions that alter the function of cellular constituents.1 This interaction results in a beneficial therapeutic effect after repeated controlled phototoxic reactions. Psoralens can be administered orally or applied topically to the skin in the form of solutions, creams, or baths. This therapy is currently used in the treatment of several common and uncommon skin diseases.
In the 1970s, it was shown that orally administered 8-methoxypsoralen (8-MOP) and subsequent irradiation with artificial UVA was a highly effective treatment for psoriasis.2,3 Psoralen baths (soaking in a dilute psoralen solution) and subsequent UVA exposure (bath-PUVA), which originated in Scandinavia,4 is also being used in many European institutions. The effectiveness of all variants of PUVA has been widely confirmed and has profoundly influenced dermatologic therapy, in general, providing treatment for numerous disorders in addition to psoriasis (Table 238-1). A major advance in phototherapy was the development of fluorescent bulbs that emitted narrowband UVB radiation at 311–313 nm in the mid-1980s. This narrow spectrum is slightly inferior in clearing psoriasis or mycosis fungoides. However, due to the fact that it is easier to perform and possibly ...