Temporal External Validation of the TWIST Prediction Tool for Time to Independent Walking after Stroke

Background. The TWIST tool uses clinical measures at 1 week post-stroke to predict whether patients will achieve independent walking by 4, 6, 9, 16 or 26 weeks post-stroke. TWIST was developed with 93 participants from 2 hospitals and was at least 83% accurate at all timepoints. Validation of TWIST is necessary before implementation into clinical practice. Objective. The study aimed to perform temporal external validation of the TWIST prediction tool in a single hospital site. Methods. Adults with stroke were recruited if they had new lower limb weakness and were unable to walk independently. A TWIST score out of 4 was calculated for each participant using age, knee extension strength and Berg Balance Test score at 1 week post-stroke. Discrimination and calibration of TWIST were calculated for each timepoint and the model was refined as required. Results. There were 89 participants in this validation cohort (43% women, median age 69 years, 56% moderate-severe stroke). Predictions were valid for most TWIST scores at most timepoints. The TWIST tool was too optimistic for participants with TWIST scores of 0 and 2 at 16 and 26 weeks, and a TWIST score of 3 at all timepoints. The TWIST tool and clinical interpretations were refined. Discrimination of the TWIST tool is good (C-statistic > 0.8) for all timepoints. Conclusions. TWIST is a temporally externally validated prediction tool that combines routine tests at 1-week post-stroke to predict the probability of an individual patient achieving independent walking by 4, 6, 9, 16 or 26 weeks post-stroke.