Optimizing the frequency of outpatient short-contact dithranol treatment used in combination with broadband ultraviolet B for psoriasis: A randomized, within-patient controlled trial

Abstract

Background: Recent concerns over the side-effects of psoralen plus ultraviolet (UV) A, immunosuppressive and cytotoxic treatments have led to increased interest in dithranol for treatment of psoriasis. Few studies have investigated how frequently dithranol should be applied. Dithranol-induced inflammation is maximal at 48-72 h, suggesting that daily application of dithranol may not be optimal. Objectives: To investigate the effectiveness of five times weekly application of short-contact dithranol (SCD) compared with three times weekly application in a dedicated hospital outpatient treatment unit. Methods: A randomized, within-patient, controlled study was performed. Patients had SCD applied five times weekly to one half of the body, and three times weekly to the other side. Whole-body UVB irradiation was given 5 days a week. Patients were assessed weekly for 8 weeks. Principal outcome measures were percentage reduction in modified Psoriasis Area and Severity Index (mPASI) at the end of study and time to 50% improvement in mPASI score. Results: Twenty-nine patients were recruited; four were excluded from analysis. Mean percentage reduction in mPASI score at the end of study for five times weekly application was 57.3% (95% confidence interval, CI 39.6-75.0%) and for three times weekly application was 55.4% (95% CI 378.73.1%; P = 0-34). Mean time to 50% improvement in mPASI for five times weekly treatment was 4.1 weeks and for three times weekly treatment was 4.0 weeks (P = 0.50). There was no difference in the frequency or severity of burning episodes for each side. Conclusions: This study suggests that three times weekly application of SCD may be as effective as five times weekly when used in conjunction with UVB administered five times weekly. Large studies of whole-body comparisons are warranted to assess further the optimal frequency of SCD and UVB therapy for psoriasis.