Could colorimetric method replace the individual minimal erythemal dose (MED) measurements in determining the initial dose of narrow‐band UVB treatment for psoriasis patients with skin phototype III–V?

Background  Assessment of minimal erythemal dose (MED) for individual patients has been used to guide the narrowband Ultraviolet B (NB‐UVB) phototherapy, which sometimes causes discomfort and additional time. The L* value (the lightness of color in Commission Internationlale de l’Eclairge L*a*b* color scale) measured by colorimeter was shown to be useful for predicting sensitivity to NB‐UVB irradiation. Objective  To compare the efficacy and safety of NB‐UVB phototherapy between 50% of MED and colorimetric L* value starting dose regimens for skin phototype III–V Korean patients with psoriasis. Method  Twenty seven patients determined starting doses based on colorimetric L* value, and 27 patients based on 50% of MED. Since correlation analysis showed that L* value had the most significant association with MED compared with skin phototypes, a*, and b* values, we designated starting doses of L* value regimen as follows: 300 mJ/cm 2 ( L* >66), 400 mJ/cm 2 (62 <  L* ≤66), and 500 mJ/cm 2 ( L* ≤62). Results  There was no significant difference between two groups in clinical efficacy including response rate, mean number of sessions, duration of treatment, maximum dose and cumulative dose until achieving the state of near clearance. The proportion of adverse effects was not also significantly different. Conclusions  NB‐UVB starting dose determination based on colorimetric L* value was comparable with conventional MED based regimen in efficacy and safety for skin phototype III–V patients. Since it provides much convenience and ease for both patients and physicians, colorimetric L* value could partly substitute the MED checking methods in NB‐UVB phototherapy.