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

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.