Frequency of phototherapy for treating psoriasis: a systematic review.

Narrow band ultraviolet B (NB-UVB) and psoralen-ultraviolet A (PUVA) remain inexpensive and effective anti-psoriatic therapies adopted worldwide with different frequency protocols. We aimed to systematically assess the evidence on the effects of different frequency protocols of phototherapy in treating psoriasis. We used the following terms, namely "photochemotherapy," "phototherapy," "psoriasis," "UVB," "UVA" and "ultraviolet therapy," to search the Cochrane Controlled Register of Trials, MEDLINE and Embase databases on August 1, 2019. We organized results using a PRISMA diagram and analyzed bias risks with RoB-2 tool. We included five randomized controlled trials (RCTs) on oral PUVA and three RCTs on NB-UVB. The five studies on PUVA included a total of 1452 patients with plaque psoriasis and did not find any significant difference in efficacy comparing two- vs. three- vs. four times weekly protocols. The three studies on NB-UVB included a total of 248 patients with plaque psoriasis. No differences in efficacy were reported in comparing different frequencies in delivering NB-UVB, namely twice vs. thrice weekly, twice vs. four times weekly, and thrice- vs. five times weekly protocols. Although protocols with higher treatments frequency per week achieved clearance faster than lower frequency ones, but they did not differ in terms of efficacy. PUVA and NB-UVB remain effective anti-psoriatic treatments; however further studies are needed to elucidate which protocol may be more effective in different skin phototypes.