THE VARIABLE RESPONSE OF PLAQUE PSORIASIS AFTER A SINGLE TREATMENT WITH TOPICAL 5-AMINOLEVULINIC ACID PHOTODYNAMIC THERAPY

We have investigated the clinical response of 22 patients with plaque psoriasis to photodynamic therapy using topical application of 5-amino laevulinic acid followed by a single exposure to broadband visible rad iation. Light doses in the range 2-16 J/cm(2) delivered at dose rates of 10-40 mW/cm(2) resulted in a variable clinical response. Seven (35% ) patients showed clearing of psoriasis at some treated sites. The int ensity of protoporphyrin IX fluorescence was recorded before, during a nd after treatment. Pre-illumination fluorescence intensity varied con siderably between sites on the same patient and between patients. Prot oporphyrin IX fluorescence recovered and persisted after treatment for up to 14 days and became higher than preillumination levels at 25% of sites. The rate of protoporphyrin IX photo-oxidation during treatment was proportional to both initial fluorescence intensity and incident light dose rate and was almost complete after 16 J/cm(2). We have defi ned the photodynamic dose as the product of time-dependent protoporphy rin IX concentration and light dose and demonstrated that only in thos e patients who showed clearance of psoriasis was there a relationship between photodynamic dose and clinical response. Discomfort ranged fro m stinging through to burning, was significant in some patients and te nded to be more severe with increasing photodynamic dose but was not p redictable. Efficacy may improve by achieving consistent protoporphyri n IX levels or by using multiple treatments.