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Updated: Aug 19, 2026
The Multiple Sclerosis Performance Test (MSPT): An iPad-Based Disability Assessment Tool
Published on: June 30, 2014
The measurement of ambulatory impairment in multiple sclerosis
S R Schwid1, A D Goodman, D H Mattson
1Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA.
Abstract:
The objective of this study was to examine the relationships between continuous measures of ambulatory impairment in MS patients and their ordinal counterparts. Much of the disability caused by MS is due to ambulatory impairment. The Expanded Disability Severity Scale (EDSS) and the Ambulation Index (AI) are ordinal measures of MS severity based largely on the maximal distance subjects can walk (Dmax) and the time to walk 8 m (T8), respectively. At EDSS levels 6.0 to 7.0 and AI levels 3 to 6, scores are defined more by the use of ambulatory aids, rather than by Dmax or T8. We determined Dmax (up to 500 m), T8, the EDSS score, and the AI in 237 ambulatory MS patients. The maximal distance subjects could walk and T8 were strongly related to their ordinal counterparts (Spearman r = 0.65 and 0.91, respectively), but the continuous measures showed considerable variability within EDSS and AI levels that the ordinal scales did not reflect. Most of the variability occurred at EDSS levels 6.0 to 7.0 and AI levels 3 to 6. Because the use of an aid did not clearly predict Dmax or T8, many patients in these ranges had better ambulatory function based on the continuous measures than those with less disability according to the ordinal scales. We found that Dmax and T8 provide more precise information about ambulatory impairment in MS than do the EDSS and AI, allowing better discrimination of differences between patients and potentially greater sensitivity to detect therapeutic effects in clinical trials.
Insights
Continuous measures of walking distance and time in multiple sclerosis (MS) patients provide more precise ambulatory impairment data than ordinal scales like the Expanded Disability Severity Scale (EDSS) and Ambulation Index (AI). This allows for better patient discrimination and detection of treatment effects.
Area of Science:
- Neurology
- Rehabilitation Medicine
- Biomedical Engineering
Background:
- Ambulatory impairment significantly contributes to disability in Multiple Sclerosis (MS).
- Ordinal scales such as the Expanded Disability Severity Scale (EDSS) and Ambulation Index (AI) are commonly used to assess MS severity.
- These ordinal scales rely heavily on walking distance (Dmax) and time (T8), but may not fully capture nuances in ambulatory function, especially when assistive devices are used.
Purpose of the Study:
- To investigate the relationship between continuous measures of ambulatory impairment (Dmax, T8) and their ordinal counterparts (EDSS, AI) in MS patients.
- To evaluate the precision and discriminatory power of continuous versus ordinal measures of ambulatory function in MS.
- To determine if continuous measures offer greater sensitivity for detecting therapeutic effects in clinical trials.
Main Methods:
- Collected data on Dmax (up to 500m), T8, EDSS scores, and AI from 237 ambulatory MS patients.
- Utilized Spearman correlation to assess the relationship between continuous and ordinal measures.
- Analyzed variability within specific EDSS and AI levels to identify discrepancies.
Main Results:
- Strong correlations were observed between Dmax and EDSS (Spearman r = 0.65) and T8 and AI (Spearman r = 0.91).
- Continuous measures revealed significant variability within EDSS levels 6.0-7.0 and AI levels 3-6, which were not reflected by the ordinal scales.
- The use of ambulatory aids did not consistently predict Dmax or T8, leading to instances where patients with lower ordinal scores exhibited better continuous functional measures.
Conclusions:
- Continuous measures of Dmax and T8 offer more precise quantification of ambulatory impairment in MS than EDSS and AI.
- These continuous metrics allow for finer discrimination between patients and potentially enhanced sensitivity in detecting treatment efficacy in MS clinical trials.
- Ordinal scales may oversimplify ambulatory function assessment, particularly in patients utilizing assistive devices.
