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UV-B phototherapy clears psoriasis through local effects
Robert S Dawe1, Heather Cameron, Susan Yule
1Photobiology Unit, Department of Dermatology, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland. r.s.dawe@dundee.ac.uk
Objective:
To determine if UV-B phototherapy clears psoriasis through systemic effects.
Design:
Randomized, within-subject comparison of change in psoriasis in 3 plaques in patients attending for whole-body UV-B therapy. Change in patients' psoriasis plaques covered during UV-B treatment was compared with plaques in an untreated control group.
Setting:
University hospital phototherapy unit.
Patients:
The study population comprised 17 patients with chronic plaque psoriasis treated with UV-B and 24 psoriasis control patients awaiting UV-B phototherapy.
Interventions:
Treatment with a standard 3-times weekly narrowband TL-01 UV-B regimen. Three similar plaques were randomly allocated to be covered every treatment, covered for 2 of 3 weekly treatments, and exposed to local UV-B every treatment. Similar plaques were selected in control patients (awaiting but not yet started UV-B therapy). Severity of psoriasis plaques was assessed using a scaling, erythema, and induration (SEI) scoring system.
Main Outcome Measures:
Change in SEI score of the selected plaques over the complete treatment course for UV-B-treated patients and change over 3 weeks in SEI score of plaques covered during UV-B treatment compared with that of plaques in controls.
Results:
There was a significant (P<.001) difference in how much the SEI score changed in the 3 plaques in UV-B-treated patients. It fell by a mean of 7.6 for uncovered plaques compared with 3.2 for plaques covered during each UV-B exposure (95% confidence interval for difference, 3.0 to 5.8). In patients awaiting UV-B, SEI score of plaques fell by a mean of 0.4 over 3 weeks, compared with a mean fall of 1.4 for covered plaques in UV-B-treated patients (95% confidence interval for difference in means, 0.1 to 2.0).
Conclusions:
If UV-B therapy has any systemic effect capable of improving psoriasis, this effect is small and unlikely to be of clinical importance. It is insufficient to alter interpretation of findings of within-subject comparative phototherapy studies. UV-B phototherapy works for chronic plaque psoriasis through local effects.