Prurigo Activity Score (PAS): validity and reliability of a new instrument to monitor chronic prurigo

Currently available tools to monitor patients with chronic prurigo over time focus on pruritus and quality of life parameters, while no instrument objectively assessing the pruriginous lesions is yet available.

The objective of this study was to develop a physician-assessed Prurigo Activity Score (PAS), a new tool to monitor the distribution and activity of chronic prurigo lesions and to evaluate its reliability and validity.

The 7-item PAS questionnaire as well as validated pruritus intensity scales (VAS, NRS) and a skin-related quality of life score (DLQI) were completed for 264 patients (172 females, age 61 years) at least twice over a period of 2 years. In addition, a 60-min test-retest reliability test was performed by four experts for a random sample of 12 patients.

The PAS showed good test-retest reliability (Cohens κ > 0.61; Cronbach-alpha > 0.76), ordinal or metric items showed high inter-rater reliability (Kendalls > 0.61) and items recording the number of lesions correlated significantly to each other (P < 0.001). The highest correlation to external constructs was achieved with DLQI. The feasibility test conducted by four raters indicated the suitability of PAS for tracking chronic prurigo in the clinical setting.

The PAS is a useful tool to objectively monitor pruriginous lesions in chronic prurigo patients over time. The sensitivity of change in the PAS score should be analysed in future studies.