Psychometric validation of the Japanese version of the lymphedema functioning, disability, and health questionnaire...

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.