Chapter 16 Topical photodynamic therapy for psoriasis

Abstract Photochemotherapy using oral psoralen and ultraviolet A radiation (PUVA) is a highly effective treatment for severe psoriasis but has carcinogenic potential. Photodynamic therapy (PDT) combining application of a photosensitizing porphyrin derivative and subsequent irradiation with red light may represent an alternative photochemotherapeutic modality with potentially a lower carcinogenic risk. In an attempt to limit potential side effects the concept of topical PDT has been persued for treating this inflammatory disease. In this context, the parameters determining susceptibility and selectivity of the targeted cell types as well as the biological effects induced in these cells could be defined. Following this pioneering work several photosensitizers were shown to exhibit good clinical efficacy in the topical PDT of psoriasis. Since the general feasibility of this approach is now well documented future studies will have to investigate the effectiveness of this modality in comparison to established regimen. Furthermore, the concept of PDT as antimicrobial regimen will have to be evaluated in the light of psoriasis being a disease triggered by bacterial superantigens.