Psychometrics and normative data for the Multiple Sclerosis Functional Composite: replacing the PASAT with the Symbol Digit Modalities Test

Abstract

The MS Functional Composite (MSFC) is a continuous scale of neurological disability for patients with multiple sclerosis (MS). Cognition is represented by the Paced Auditory Serial Addition Test (PASAT), although the Symbol Digit Modalities Test (SDMT) has been proposed as a promising alternative. MSFC scores were calculated using either the PASAT or the SDMT with the following reference populations: National Multiple Sclerosis Society (NMSS) Task Force, 400 MS patients, and 100 normal controls. A subgroup of 115 patients was followed longitudinally, with a test-retest interval of 2.3 +/- 1.2 years. Pearson correlations were calculated and analyses of variance (ANOVAs) were used to assess relationships among the MSFC components and composite scores, and differences in performance between patients and controls. Longitudinal changes were also assessed. Logistic regression was performed to determine which MSFC scores are most predictive of diagnosis, course, and work disability. All MSFCs had similar test-retest reliability and correlations with other measures including neurological disability, depression, and fatigue. The SDMT showed slightly better validity with respect to predicting diagnosis, course, and work disability, although the amount of variance accounted for was similar for each version of the MSFC. Our data, derived from a large sample of MS patients and normal controls, supports the validity of both PASAT and SDMT versions of the MSFC. Because the SDMT has slightly better predictive validity and has a relatively easier administration procedure, some clinicians and researchers may wish to replace the PASAT with the SDMT in future calculations of the MSFC using the calculation methods provided in this manuscript.

Factors Associated with Employment Status in Individuals with Multiple Sclerosis

“…Recent studies have suggested replacing the Paced Auditory Serial Addition Test in the MSFC with the Symbol Digit Modalities Test, and the results of the present study are consistent with this suggestion. 42,43 A potential limitation of this study is the small sample size (N = 53), a factor that may limit the ability to detect small effect sizes. In addition, this study sample was predominantly women (85%), and, thus, its findings may not generalize to men.…”

The contribution of MRI in assessing cognitive impairment in multiple sclerosis

“…A study in a large group of patients with MS and controls demonstrated the validity of both the PASAT and SDMT version of the MSFC, with slightly better ability of the SDMT version in predicting diagnosis, disease course, and work disability. 9 The SDMT is also among the more reliable and sensitive 10 tests in the MS literature and is a robust correlate of several brain imaging findings.…”

Paced auditory serial addition test (PASAT): a very difficult test even for individuals with high intellectual capability

“…Patients have an aversive feeling towards PASAT 12 , unaware that bad scores may not reflect neurological impairment 11 . Recent studies have even suggested that PASAT should be replaced by another test for MSFC assessment 13 .…”