The effects of keratolytic pretreatment prior to fluorescence diagnosis and photodynamic therapy with aminolevulinic acid-induced porphyrins in psoriasis

Background: Psoriasis lesions accumulate protoporphyrin IX (PpIX) with a variable distribution within plaques due to variations in hyperkeratosis causing differences in penetration of cream or light. Objectives: To study the effects of different keratolytic pretreatments in PpIX-induced fluorescence diagnosis (FDAP) and during photodynamic therapy (PDT). Methods: Two psoriasis plaques of 10 patients were treated with either topical retinoic acid or with a hydrocolloid dressing. The hydrocolloid dressing gave the best results. Subsequently, two different contralateral plaques of eight patients were pretreated with a hydrocolloid dressing or the standard pretreatment, salicylic acid in petrolatum, during the 6 weeks of PDT. Biopsies were investigated with respect to stratum corneum thickness, proliferation, differentiation and inflammation. Results: Irritation and point bleedings were noticed after retinoic acid. A hydrocolloid dressing induced the best clinical improvement. Therefore, it was used as alternative pretreatment for psoriasis prior to PDT. We observed significant clinical and immunohistochemical improvement of psoriasis in the salicylic acid as well as the hydrocolloid dressing pretreated plaques. Conclusions: Salicylic acid in petrolatum and a hydrocolloid dressing prior to FDAP and PDT induce improvement of hyperkeratosis. Thus, a hydrocolloid dressing is a good alternative to the current keratolytic pretreatment regime.