Estimation of minimal clinically important difference for 6-minute walking distance in patients with acute stroke using anchor-based methods and credibility instruments

Background and Purpose: Stroke impairs a patient's ability to walk. In patients with acute stroke, a 6-min walking distance (6MWD) is recommended to assess walking function. Minimal clinically important difference (MCID) is used to determine the effectiveness of rehabilitation; however, the MCID for 6MWD has not been adequately validated. This study aimed to estimate the MCID of 6MWD, a measure of walking endurance, in patients with acute stroke using anchor-based methods. Methods: Based on the change in 6MWD from baseline to the follow-up measurement 2 weeks later, the MCID was estimated using anchor-based methods (receiver operator operating characteristic curves, predictive and adjustment models) with a patient- and therapist-rated global rating of change scale (p-GRC, t-GRC) as external anchors. The accuracy of "meaningful change" was estimated from the area under the curve. Using MCID's credibility instruments, the credibility of each anchor was evaluated. Using the credibility instrument, high credibility was defined as satisfying 3/5 of the Core criteria and 6/9 of all criteria. Results: The analysis included 58 patients. The MCID for each anchor was 78.7-100.0 m for p-GRC, and 95.2-99.5 m for t-GRC. The p-GRC demonstrated excellent accuracy (area under the curve >0.8). With p-GRC as anchors, over 50% of patients showed improvement. The p-GRC satisfied the core criterion of 3/5 and all criteria of 6/9 on the reliability instrument. The t-GRC demonstrated low reliability and satisfied the core criterion of 2/5 and all criteria of 3/9. Discussion: Since the percentage of improved groups exceeded 50%, the adjusted model was useful in the anchor-based method. Therapists may not accurately capture patient fatigue and subjective symptoms, potentially affecting the correlation between the 6MWD change score and the t-GRC and, consequently, the reliability instrument. The p-GRC showed high accuracy and reliability; therefore, the MCID was estimated to be 78.7 m.