Profiling cognitive–motor interference in a large sample of persons with progressive multiple sclerosis and impaired processing speed: results from the CogEx study

Background: Performing cognitive–motor dual tasks (DTs) may result in reduced walking speed and cognitive performance. The effect in persons with progressive multiple sclerosis (pwPMS) having cognitive dysfunction is unknown. Objective: To profile DT-performance during walking in cognitively impaired pwPMS and examine DT-performance by disability level. Methods: Secondary analyses were conducted on baseline data from the CogEx-study. Participants, enrolled with Symbol Digit Modalities Test 1.282 standard deviations below normative value, performed a cognitive single task ([ST], alternating alphabet), motor ST (walking) and DT (both). Outcomes were number of correct answers on the alternating alphabet task, walking speed, and DT-cost (DTC: decline in performance relative to the ST). Outcomes were compared between EDSS subgroups (≤ 4, 4.5–5.5, ≥ 6). Spearman correlations were conducted between the DTC_motor with clinical measures. Adjusted significance level was 0.01. Results: Overall, participants (n = 307) walked slower and had fewer correct answers on the DT versus ST (both p < 0.001), with a DTC_motor of 15.8% and DTC_cognitive of 2.7%. All three subgroups walked slower during the DT versus ST, with DTC_motor different from zero (p’s < 0.001). Only the EDSS ≥ 6 group had fewer correct answers on the DT versus ST (p < 0.001), but the DTC_cognitive did not differ from zero for any of the groups (p ≥ 0.039). Conclusion: Dual tasking substantially affects walking performance in cognitively impaired pwPMS, to a similar degree for EDSS subgroups.