Confirmed Worsening in the Symbol Digit Modalities Test and Timed 25-Foot Walk in Routine Multiple Sclerosis Care: A Retrospective Single-Center Longitudinal Study

Abstract

Objective

Performance-based monitoring in multiple sclerosis (MS) is widely used, yet objective deterioration in routine regional practice is not well quantified. We aimed to estimate 24-month trajectories of cognitive processing speed and ambulation and to quantify confirmed worsening in these performance measures.

Methods

We performed a retrospective, single-center longitudinal study of 59 patients with repeated Symbol Digit Modalities Test (SDMT) and/or Timed 25-Foot Walk (T25FW) assessments. Linear mixed-effects models with random intercepts estimated marginal means at 0, 6, 12, 18, and 24 months, adjusting for prespecified covariates. T25FW was modeled on the log scale; unmeasurable T25FW was summarized separately. Confirmed performance worsening was defined as at least a 4-point SDMT decline or at least a 20% T25FW increase from baseline, confirmed at a reassessment at least 6 months later. Inference was restricted to 0–24 months.

Results

Mean changes over 24 months were small, but observed paired changes varied widely. Confirmed performance worsening occurred in 7/59 patients (11.9%) for SDMT and 8/56 (14.3%) for T25FW (among those measurable at baseline). Unmeasurable T25FW was present in 3/59 (5.1%) at baseline and occurred during follow-up in 2/56 (3.6%) of baseline-measurable patients.

Conclusion

In routine regional MS care, approximately one in eight patients met criteria for confirmed worsening in SDMT or T25FW during the 24-month observation period despite modest mean trends. Longitudinal monitoring should also capture transitions to unmeasurable walking status.