Rasch validation and refinement of the Lymphedema Life Impact Scale version 2 in an Italian cohort with secondary lymphedema

Abstract

Purpose To produce and validate an Italian version of the Lymphedema Life Impact Scale version 2 (LLISv2-It), a tool measuring the impact of lymphedema on health-related quality of life, and investigate its main psychometric characteristics. Methods After translation and cross-cultural adaptation of the LLISv2, we administered it to 156 subjects with secondary lymphedema (upper or lower limb), together with (depending on the limb involved) either the Disabilities of the Arm, Shoulder and Hand questionnaire (DASH) or the Lower Extremity Functional Scale (LEFS). We analyzed the performance of LLISv2-It using Classical Test Theory and Rasch methods. Results Cronbach alpha was 0.89. Item fit statistics indicated that item #12 was underfitting (Infit MnSQ = 1.56; Outfit MnSq = 1.75). Test-retest reliability of the 17-item version (without item #18, not scored, according to the original authors) and of a 16-item version (without #12 and #18—a unidimensional item set) were both excellent (ICC2.1 = 0.93; 95%). The minimum detectable change was 8.9 points. The correlation of LLISv2-It with DASH and LEFS was r = 0.81 and −0.57, respectively. Conclusions The Italian version of the LLISv2 is reliable and valid. To make the tool more psychometrically sound, we recommend to not calculate items #12 and #18 in the total score. IMPLICATIONS FOR REHABILITATION The Lymphedema Life Impact Scale (LLISv2) is particularly useful as a validated condition-specific health-related quality of life measure for patients with chronic edema/lymphedema. We have validated its Italian version (LLISv2-It). We also examined the psychometric properties of the LLISv2 in individuals with secondary lymphedema of either upper or lower limb, using both classical test theory and Rasch techniques, to provide insights for further refinement of the questionnaire. Based on our results, we recommend not to count item #12 in the total score (besides #18, as already suggested by the original authors). Moreover, we determined that the minimum detectable change of the LLISv2 was 9 points. This information is helpful in clinical practice to understand if the change in score is not due to chance (measurement error). Although further research is warranted, the present validation study of the LLISv2 increases the confidence in the metric quality and clinical utility of the scale to assess lymphedema-specific health-related quality of life in individuals with secondary lymphedema of either upper or lower limb.