Photodynamic therapy induces less pain in patients treated with methyl aminolevulinate compared to aminolevulinic acid

Photodynamic therapy (PDT) with topical application of either aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) is increasingly used for the treatment of actinic keratoses (AKs). Although PDT is a well-tolerated treatment, pain is the most severe side effect. Sixty-nine patients (mean age 69 years, 61 male, 8 female) suffering from multiple AKs on the scalp (field cancerization) were included in the study. PDT treatment was performed, using red light (Waldmann PDT 1200) with a light dose of 100 J/cm2 delivered at a dose rate of 160 mW/cm2. Either ALA or MAL were used as photosensitizer. Patients were asked to rate their pain on a scale from 0 to 10 (0 = no pain, 10 = unbearable pain). Upon reaching a score of 10 treatment was discontinued. Comparison of ALA and MAL in patients with AK revealed that MAL induced less pain than ALA. While 14% of the patients treated with MAL discontinued treatment before reaching the required light dose of 100 J/cm2, the number of patients treated with ALA who discontinued treatment reached 54%. PDT using MAL appears to be a better tolerated treatment for multiple AKs on the scalp compared to ALA-PDT. Differences in selectivity for tumor cells and transport of ALA in peripheral neurons may play a role.