Background Itching is a subjective and multidimensional experience which is difficult to quantify. Most methodologies to assess itching suffer from being unidimensional, for example only measuring intensity without impact on quality of life, or only measuring scratching activity. None has actually been demonstrated to be able to detect change over time, which is essential to using them as an outcome measure of response to an intervention. The 5-D itch scale was developed as a brief but multidimensional questionnaire designed to be useful as an outcome measure in clinical trials. The five dimensions are degree, duration, direction, disability and distribution. Objectives To study the 5-D with respect to validity, reliability and response to change. Methods The 5-D was administered to 234 individuals with chronic pruritus due to liver disease (n = 63), kidney disease (n = 36), dermatological disorders (n = 56), HIV/AIDS (n = 28) and burn injuries (n = 51). The 5-D was administered at baseline and after a 6-week follow-up period. A subset of 50 untreated patients was retested after 3 days to assess test-retest reliability. Results The 5-D score correlated strongly with a visual analogue score: r = 0·727 at baseline (P < 0·0001), r = 0·868 at the 3-day repeat (P < 0·0001), and r = 0·892 at the 6-week follow-up (P < 0·0001). There was no change in mean 5-D score between day 1 and day 3 in untreated individuals (intraclass correlation coefficient = 0·96, P < 0·0001). The 5-D did, however, detect significant changes in pruritus over the 6-week follow-up period (P < 0·0001). Subanalysis of the different patient groups revealed similar response patterns and scores, with the exception of lower total scores for the burn victims due to lower scores on the distribution domain because they itched only at the site of their burn. Conclusions The 5-D, therefore, is a reliable, multidimensional measure of itching that has been validated in patients with chronic pruritus to able to detect changes over time. The 5-D should be useful as an outcome measure in clinical trials.
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