External validation and update of minimal important change in the 6-minute walk test in hospitalized patients with subacute stroke.

Objective: To investigate the external validation of the previously reported minimal important change (MIC) in the 6-minute walk test (6MWT) and update it for patients with subacute stroke hospitalized in rehabilitation unit.

Design: Longitudinal study SETTING: : Rehabilitation unit of a neurosurgical hospital.

Participants: One hundred and seven patients with subacute stroke.

Intervention: Not applicable.

Main outcome measure(s): The 6MWT, modified Rankin Scale (mRS), Functional Ambulation Categories (FAC), and Functional Independence Measure (FIM) were assessed at 30 (baseline) and 60 (follow-up) days after stroke onset. Patients were divided into two groups according to improvements of mRS by ≥1, FAC by ≥1, or FIM by ≥22. The change in the 6MWT between baseline and follow-up was calculated and patients were divided into two groups according to improvements of 6MWT by ≥71 m. External validation was performed using likelihood ratio (LR) between change of 6MWT by ≥71 m and improvement of mRS. An LR+>2.0 and LR-<0.5 was considered valid. The new MIC of the 6MWT was calculated for the mRS, FAC, and FIM using the receiver operating characteristic curve (MIC_ROC) and adjusted predictive modeling method (MIC_adjusted).

Results: No external validation was achieved (LR+ of 1.41, LR- of 0.77). The MIC_ROC values for mRS, FAC, and FIM were 22.0 m, 69.0 m, and 22.0 m, respectively. The MIC_adjusted values for the mRS, FAC, and FIM were 68.7 m, 63.1 m, and 83.1 m, respectively. Only the MIC of the 6MWT for FAC was validated.

Conclusions: The previously reported MIC of the 6MWT was not suitable for patients with subacute stroke hospitalized in rehabilitation units; however, the newly determined MIC was useful.