Itch and scratching as predictors of time to clearance of psoriasis with narrow-band ultraviolet B therapy

Background Narrow-band ultraviolet (UV) B phototherapy is an effective treatment for psoriasis. However, there is considerable variability in the number of treatment sessions needed to achieve psoriasis clearance. While several clinical and treatment-related factors predict time to clearance, the effect of itching and scratching on the number of irradiation sessions is insufficiently understood. Objective Predictors of the time to clearance were assessed in patients with psoriasis who were referred for UVB treatment in a randomized double-blind comparison of irradiation regimens for UVB phototherapy. Methods After randomization to either UVB irradiation with a suberythematogenic or an erythematogenic regimen, patients were irradiated with 20% and 40% incremental doses, respectively, three times weekly. The Psoriasis Area and Severity Index (PASI) score was measured at baseline and every 4 weeks, and itching and habitual scratching were measured at baseline. Results Among the 77 patients who achieved psoriasis clearance (90% reduction of PASI), itching and scratching were correlated with the number of irradiation sessions needed to achieve clearance, with higher levels of itch and scratching predicting more sessions. These effects remained significant after controlling for the initial PASI score, irradiation schemes, minimal erythema dose (MED), skin type, cumulative dose, protocol adjustments and lifestyle factors (smoking habits and alcohol consumption). Conclusions Patients with higher levels of itch and scratching need more irradiation sessions to achieve clearance of psoriasis with UVB phototherapy. Systematic assessment of the severity of itch and scratching, followed by short-term itch-coping programmes for patients at risk, might be a cost-effective, adjunct to UVB therapy.