Psychometric validation of the Japanese version of the lymphedema functioning, disability, and health questionnaire for upper limb lymphedema: A multicenter cross-sectional study

Upper limb lymphedema that develops after breast cancer treatment affects not only patients' physical function and daily activities but also their psychosocial well-being, thereby reducing their health-related quality of life (HRQOL). The Lymphedema Functioning, Disability, and Health Questionnaire for Upper Limb Lymphedema (Lymph-ICF-UL) is a scale that comprehensively evaluates these effects. However, a Japanese version is not yet available. This study aimed to translate and develop a Japanese version of the Lymph-ICF-UL and to verify its psychometric properties in patients with breast cancer-related upper limb lymphedema. The scale was translated in accordance with international guidelines. A total of 208 women from 3 facilities in Japan completed the questionnaire. For test-retest reliability, 142 participants were randomly selected, among whom 131 completed the retest. Content validity was evaluated by 21 experts, and internal consistency and test-retest reliability were verified. For construct validity, exploratory and confirmatory factor analyses were conducted, and convergent and discriminant validities were evaluated using subscales of the 36-Item Short-Form Health Survey Questionnaire. The Japanese version of the Lymph-ICF-UL demonstrated acceptable content validity, high internal consistency, and good test-retest reliability. Exploratory and confirmatory factor analyses provided partial support for the original five-factor structure; however, some model fit indices did not meet conventional thresholds. The forced five-factor model with low-loading items removed showed the lowest Bayesian information criterion. Convergent validity was supported for all predefined hypotheses, whereas discriminant validity was supported for 4 of 9 hypotheses, resulting in confirmation of 64% of all hypotheses. The Japanese version of the Lymph-ICF-UL has been demonstrated to have sufficient reliability and validity. This scale is a practical assessment tool for evaluating the HRQOL in patients with upper limb lymphedema.