Psoriasis may be treated with ultraviolet B from lamps which have a broad emission spectrum or, more effectively, with lamps that have a narrow emission spectrum at 311±2 nm. There are conflicting reports of either greater or lesser burning episodes with narrow band compared to broadband ultraviolet B. even when treatments are based on predetermined minimal erythema dose measurements. This suggests that either the characteristics of the dose-response curve for erythema or the time-course for erythema may be different for the two lamps.
We examined the erythemal response to narrowband and broadband ultraviolet B in 12 patients with psoriasis. A geometric series of 10 doses from each lamp type were used on non-lesional skin on the back. Dose-response curves were constructed from reflectance measurements of erythema at 24 h and 72 h after irradiation.
No significant difference was found in steepness of the erythema dose-response curve for the two lamps at 24 or 72 h, Persistence of erythema was assessed as the percentage of erythema remaining at 72 h. The mean persistence was 63% for narrow~band and 64% for broadband lamps (p=0.94). Therefore, in terms of erythemal response, no evidence has been found for a difference in burning potential for the two lamps.
Das S, Lloyd JJ, Farr PM. A comparison of Erythema induced by Broad-band and narrow-band ultraviolet fluorescent lamps Journal of Investigative Dermatology, 2001.
Dr. Jim Lloyd, RVI Unit, Newcastle upon Tyne. Tel: +44 (0)191-233-6161.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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