The symbol digit modalities test and the paced auditory serial addition test involve more than processing speed.

BACKGROUND: Slowed processing speed is the most frequently reported cognitive deficit for people with multiple sclerosis (MS). However, measures used to assess processing speed may also recruit other cognitive abilities. The present objective was to determine the contributions of different cognitive functions to performance on two commonly used processing speed measures: the Symbol Digit Modalities Test (SDMT) and the Paced Auditory Serial Addition Test (PASAT). METHODS: Adults with relapsing-remitting MS (n = 70) and controls (n = 72) completed the SDMT, PASAT, and multiple measures assessing processing speed, working memory, and learning. Hierarchical regression analyses were used to examine the contributions of MS, processing speed, working memory, learning, and all possible interactions among factors to SDMT and PASAT scores. RESULTS: Processing speed and working memory generally contributed to performance on the SDMT and PASAT, with learning additionally contributing to SDMT performance. However, significant interactions revealed processing speed did not influence PASAT performance for individuals with high working memory ability whereas processing speed became increasingly more important as working memory declined to average and low levels. Further, processing speed was associated with SDMT performance for patients with MS but not controls. CONCLUSIONS: These findings support a multifactorial interpretation of the SDMT and PASAT, which facilitates their usefulness as screening measures for cognitive decline but prevents them from identifying which specific cognitive functions are affected.

Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS): Canadian contribution to the international validation project.

BACKGROUND: Given the high prevalence of cognitive dysfunction in people with multiple sclerosis (PWMS) and the lack of availability of specialized neuropsychological services in most MS Clinics, there is a need for a brief cognitive monitoring tool that can be easily administered by MS clinic staff. OBJECTIVE: We aimed to establish the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) as a feasible cognitive monitoring tool and provide Canadian data toward the international validation effort. Secondary considerations were to determine if BICAMS correlates with self-reported cognition and predicted vocational status. METHODS: 57 PWMS were matched to 51 healthy controls (age, sex, education). Participants completed the BICAMS battery which includes the Symbol Digit Modalities Test, and the learning trials from the California Verbal Learning Test-II and the Brief Visuospatial Memory Test-Revised. Depression, self-reported cognition, and fatigue were assessed. Participants were re-tested 15.6 (SD 2.0) days later. RESULTS: With impairment defined as "one or more abnormal tests," 57.9% of MS sample was cognitively impaired. Participants were more likely to be impaired on the BVMT-R (43.9%). On the SDMT and CVLT-II, 28.1% and 26.3% of MS participants were impaired. Sensitivity and specificity were highest for the SDMT. The BICAMS was reliable over time (r value range from 0.69 for BVMT-R to 0.87 for SDMT) with the SDMT being most robust. There was no relationship between BICAMS and subjective cognition. The BVMT-R reliably predicted employment. CONCLUSIONS: The BICAMS detected cognitive impairment to a comparable degree to more comprehensive neuropsychological batteries and is a valid measure of cognition in MS. Reliability of components varies, suggesting care be taken when interpreting serial testing results. The BICAMS is a feasible cognitive assessment tool in Canadians and yields comparable results to other cultures.

Reliability of regression-based normative data for the oral symbol digit modalities test: an evaluation of demographic influences, construct validity, and impairment classification rates in multiple sclerosis samples.

The oral Symbol Digit Modalities Test (SDMT) has been recommended to assess cognition for multiple sclerosis (MS) patients. However, the lack of adequate normative data has limited its clinical utility. Recently published regression-based norms may resolve this limitation but, because these norms were derived from a relatively small sample, their stability is unclear. We aimed to evaluate the stability of regression-based SDMT norms by comparing existing norms to a cross-validation dataset. First, regression-based normative data were created from a similarly-sized, independent, control sample (n = 94). Next the original and cross-validation norms were compared for equivalency, management of demographic influences, construct validity, and impairment classification rates in a mildly affected MS sample (n = 70). Lastly, similar comparisons were made for a large, representative MS clinic sample (n = 354). We found construct validity and management of demographic influences were equivalent for the two sets of regression-based norms but lower T-scores were obtained using the original dataset, resulting in discrepancies in impairment classification. In conclusion, regression-based norms for the oral SDMT attenuate demographic influences and possess adequate construct validity. However, norms generated using small samples may yield unreliable classification of cognitive impairment. Larger, representative databases will be necessary to improve the clinical utility of regression-based norms.

Cognition in early relapsing-remitting multiple sclerosis: consequences may be relative to working memory.

The Relative Consequence Model proposes multiple sclerosis (MS) patients have a fundamental deficit in processing speed that compromises other cognitive functions. The present study examined the mediating role of processing speed,as well as working memory, in the MS-related effects on other cognitive functions for early relapsing-remitting patients. Seventy relapsing-remitting MS patients with disease duration not greater than 10 years and 72 controls completed tasks assessing processing speed, working memory, learning, and executive functioning. The possible mediating roles of speed and working memory in the MS-related effects on other cognitive functions were evaluated using structural equation modeling. Processing speed was not significantly related to group membership and could not have a mediating role. Working memory was related to group membership and functioned as a mediating/intervening factor. The results do not support the Relative Consequence Model in this sample and they challenge the notion that working memory impairment only emerges at later disease stages. The results do support a mediating/intervening role of working memory. These results were obtained for early relapsing-remitting MS patients and should not be generalized to the broader MS population. Instead, future research should examine the relations that exist at other disease stages.

Tests of information processing speed: what do people with multiple sclerosis think about them?

Reduction in information processing speed (IPS) is a key deficit in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT), Symbol Digit Modalities Test (SDMT), and Computerized Test of Information Processing (CTIP) are used to measure IPS. Both the PASAT and SDMT are sensitive to deficits in IPS. The CTIP, a newer task, also shows promise. The PASAT has several limitations, and it is often perceived negatively by patients. Yet little supporting quantitative evidence of such perceptions has been presented. Therefore, in this study, subjective ratings of likeability, difficulty, and appropriateness of the PASAT, CTIP, and SDMT were obtained. Ratings were compared between MS patients and healthy controls. It was hypothesized that ratings of the PASAT would differ significantly from those of the SDMT and CTIP. The relationship between subjective ratings and objective performance was evaluated. Sixty-nine MS patients and 68 matched controls rated the three tests in terms of likeability, difficulty, and appropriateness for capturing cognitive deficits often associated with MS using a Likert scale. Both groups rated the PASAT as most difficult and least likeable. The MS group rated the PASAT and SDMT as more appropriate for measuring MS-related deficits than the CTIP. Subjects who performed better on the PASAT were more likely to rate it as easier. Ratings of the SDMT and CTIP did not vary consistently with performance. The findings lend quantitative support to the common belief that the PASAT is perceived as unpleasant. Other tests are available that are similarly sensitive to deficits in IPS and more palatable to the patient.