Validation of 'ItchApp©' in Poland and in the USA: multicentre validation study of an electronical diary for the assessment of pruritus.

BACKGROUND: Although chronic pruritus affects a large part of the population, its reliable assessment remains difficult. Electronical diaries (eDiaries) are often used in multicentre clinical trials. The ItchApp© for Android was developed to assess itch intensity and course and was validated for the German language in 2017. OBJECTIVE: To validate ItchApp© for the use in the Polish and US English languages. METHODS: Fifty-three subjects in Poland and thirty subjects in the USA with chronic pruritus completed the paper-based and app-based questionnaires. These questionnaires contained items for measuring the itch intensity, including a numerical rating scale (NRS) and verbal rating scale (VRS), and for detecting the change of pruritus since the beginning of treatment. RESULTS: The ItchApp© showed a high level of test-retest reliability [Intraclass correlation, Kappa and Kendall-Tau B coefficients: 0.915-1.000 (Poland) and 0.863-1.000 (USA)]. The convergent validity showed strong correlation between the itch intensity scales on the ItchApp© (Items II-IV = VRS mean, NRS mean and NRS worst) and the paper-based itch intensity scales (mean and worst: VRS, NRS, VAS) [Spearman-Rho and Pearson correlation coefficients: 0.710-0.987 (Poland) and 0.646-0.954 (USA)]. The ItchApp© items moderately correlated with the ItchyQol scores [Spearman-Rho and Pearson correlation coefficients: 0.303-0.554 (Poland) and 0.275-0.447 (USA)]. After completing the ItchApp© questionnaire, a feasibility questionnaire was completed and showed that subjects feel the app is well suited for assessing pruritus. CONCLUSION: We provide evidence for the ItchApp© as a validated eDiary for the assessment of pruritus in Polish and US English languages, enabling its use in multicentre international clinical trials.