Assessing the reliability and validity of the Italian EQ-5D-5 L in multiple sclerosis: a cross-sectional study

BACKGROUND: Multiple Sclerosis (MS) significantly affects physical, cognitive, and psychosocial functioning, leading to impaired Health-Related Quality of Life (HRQoL). The EQ-5D-5 L is a widely used generic patient-reported outcome measure (PROM) to assess HRQoL across health conditions. However, its psychometric properties have not been fully established in Italian people with MS (PwMS). This study aimed to evaluate the reliability and validity of the Italian EQ-5D-5 L in PwMS, supporting its applicability in clinical and research contexts. METHODOLOGY: A cross-sectional psychometric validation study was conducted in accordance with COSMIN guidelines. Participants were recruited from an Italian tertiary MS center based on the following inclusion criteria: age ≥ 18 years, confirmed MS diagnosis according to the 2017 McDonald criteria, fluency in Italian, and ability to provide informed consent and independently complete the questionnaire. Eligible participants completed the Italian EQ-5D-5 L and the MSQOL-54 in person. Test-retest reliability was assessed via Intraclass Correlation Coefficients (ICC) after a 48-hour interval in clinically stable participants, construct validity through Pearson's correlations with MSQOL-54 domains, and known-groups validity by ANOVA and t-tests across disability levels (EDSS), employment status, and physiotherapy engagement. RESULTS: Sixty-nine PwMS (55% female; mean age 49 ± 13 years) were included. The EQ-5D-5 L showed high test-retest reliability (ICC range = 0.81-0.95). Strong correlations supported construct validity, particularly between the EQ-Index and the Physical Health Composite Score (r = 0.76, p < 0.001) and between the EQ-VAS and the Overall Quality of Life item (r = 0.71, p < 0.001). Known-groups validity was confirmed, with higher HRQoL scores among participants with mild disability (EDSS 0-3.5) and those employed (both p < 0.001). CONCLUSIONS: The Italian EQ-5D-5 L showed satisfactory reliability and construct validity in PwMS, supporting its use as a generic measure of HRQoL in clinical and research settings. The relatively small sample size, particularly in the test-retest subgroup, should be considered when interpreting these findings. Additional measurement properties, including content validity, were not specifically evaluated in the present study. Complementary use with MS-specific instruments remains advisable to capture domains such as fatigue and cognitive function.