Photodynamic therapy leads to significant improvement of actinic keratosis area and severity index (AKASI).

Abstract Background Actinic keratosis area and severity index (AKASI) is a new quantitative tool for assessing AK severity on the head and can be used to monitor outcomes of different therapies. The aim of this study was to determine treatment outcomes of AK applying AKASI three months after conventional photodynamic therapy (PDT). Methods We performed a retrospective analysis of patients who have undergone PDT on the head and had a documented AKASI evaluation prior to PDT and at follow-up visits. Results Of the 33 patients included, 32 (97.0%) patients showed an AKASI reduction and 1 (3.0%) patient an increase of AKASI at follow-up visits compared to baseline. The median (range) follow-up period was 96 days (70–161). The median difference of AKASI values between both visits was 73.7% (−34.8 to 100.0%). The Wilcoxon test showed highly significant differences (P  The Mann–Whitney U test showed in a subgroup analysis of patients with a positive history of at least more than one intervention and treatment naive patients significant differences in these two groups (P = 0.0302). Conclusions AKASI represents a feasible and comparable tool for objectively assessing field-directed treatment modalities such as PDT in daily routine. The establishment of AKASI 50, 75, 100 serves as an objective measure to compare treatment outcomes to baseline severity of AK.