Cognitive processing speed deficits in multiple sclerosis: Dissociating sensorial and motor processing changes from cognitive processing speed

The complex relation between visual complaints and decline in visual, visuoperceptual and cognitive functions in people with multiple sclerosis

People with multiple sclerosis (pwMS) report many different visual complaints, but not all of them are well understood. Decline in visual, visuoperceptual and cognitive functions do occur in pwMS, but it is unclear to what extend those help us understand visual complaints. The purpose of this cross-sectional study was to explore the relation between visual complaints and decline in visual, visuoperceptual and cognitive functions, to optimize care for pwMS. Visual, visuoperceptual and cognitive functions of 68 pwMS with visual complaints and 37 pwMS with no or minimal visual complaints were assessed. The frequency of functional decline was compared between the two groups and correlations were calculated between visual complaints and the assessed functions. Decline in several functions occurred more frequently in pwMS with visual complaints. Visual complaints may be an indication of declined visual or cognitive functioning. However, as most correlations were not significant or weak, we cannot infer that visual complaints are directly related to functions. The relationship may be indirect and more complex. Future research could focus on the overarching cognitive capacity that may contribute to visual complaints. Further research into these and other explanations for visual complaints could help us to provide appropriate care for pwMS.

Visuo-Cognitive Phenotypes in Early Multiple Sclerosis: A Multisystem Model of Visual Processing

BACKGROUND

Cognitive impairment can emerge in the earliest stages of multiple sclerosis (MS), with heterogeneity in cognitive deficits often hindering symptom identification and management. Sensory-motor dysfunction, such as visual processing impairment, is also common in early disease and can impact neuropsychological task performance in MS. However, cognitive phenotype research in MS does not currently consider the relationship between early cognitive changes and visual processing impairment.

OBJECTIVES

This study explored the relationship between cognition and visual processing in early MS by adopting a three-system model of afferent sensory, central cognitive and efferent ocular motor visual processing to identify distinct visuo-cognitive phenotypes.

METHODS

Patients with clinically isolated syndrome and relapsing-remitting MS underwent neuro-ophthalmic, ocular motor and neuropsychological evaluation to assess each visual processing system. The factor structure of ocular motor variables was examined using exploratory factor analysis, and phenotypes were identified using latent profile analysis.

RESULTS

Analyses revealed three ocular-motor constructs (cognitive control, cognitive processing speed and basic visual processing) and four visuo-cognitive phenotypes (early visual changes, efferent-cognitive, cognitive control and afferent-processing speed). While the efferent-cognitive phenotype was present in significantly older patients than was the early visual changes phenotype, there were no other demographic differences between phenotypes. The efferent-cognitive and cognitive control phenotypes had poorer performance on the Symbol Digit Modalities Test compared to that of other phenotypes; however, no other differences in performance were detected.

CONCLUSION

Our findings suggest that distinct visual processing deficits in early MS may differentially impact cognition, which is not captured using standard neuropsychological evaluation. Further research may facilitate improved symptom identification and intervention in early disease.

Working Memory Phenotypes in Early Multiple Sclerosis: Appraisal of Phenotype Frequency, Progression and Test Sensitivity

Working memory (WM) impairments are common and debilitating symptoms of multiple sclerosis (MS), often emerging early in the disease. Predominantly, WM impairments are considered in a binary manner, with patients considered either impaired or not based on a single test. However, WM is comprised of different activated subcomponents depending upon the type of information (auditory, visual) and integration requirements. As such, unique WM impairment phenotypes occur. We aimed to determine the most frequent WM phenotypes in early MS, how they progress and which WM test(s) provide the best measure of WM impairment. A total of 88 participants (63 early relapsing–remitting MS: RRMS, 25 healthy controls) completed five WM tests (visual–spatial, auditory, episodic, executive) as well as the symbol digit modalities test as a measure of processing speed. RRMS patients were followed-up for two years. Factors affecting WM (age/gender/intelligence/mood) and MS factors (disease duration/disability) were also evaluated. Some 61.9% of RRMS patients were impaired on at least one WM subcomponent. The most subcomponents impaired were visual,–spatial and auditory WM. The most common WM phenotypes were; (1) visual–spatial sketchpad + episodic buffer + phonological loop + central executive, (2) visual–spatial sketchpad + central executive. The test of visual–spatial WM provided the best diagnostic accuracy for detecting WM impairment and progression. The SDMT did not achieve diagnostic accuracy greater than chance. Although this may be unsurprising, given that the SDMT is a measure of cognitive processing speed in MS, this does highlight the limitation of the SDMT as a general screening tool for cognitive impairment in early MS.

Cognitive Processing Speed Impairment Does Not Influence the Construct Validity of Six-Spot Step Test Performance in People With Multiple Sclerosis

OBJECTIVE

There is evidence supporting the construct validity of Six-Spot Step Test (SSST) performance as a functional mobility measure in people with multiple sclerosis (MS); however, it is unknown if cognitive processing speed impairment confounds the construct validity of SSST performance in MS, as this test seemingly requires intact cognitive processing. The objective of this study was to examine the influence of cognitive processing speed impairment on the construct validity and precision of SSST performance as a functional mobility measure in MS.

METHODS

Participants (N = 213) completed the SSST, timed 25-foot walk, 6-Minute Walk Test, Timed "Up and Go" Test, Multiple Sclerosis Walking Scale-12, device-measured steps per day, and Late-Life Function and Disability Inventory, Patient-Determined Disease Steps, and the Symbol-Digit Modalities Test as a cognitive processing speed measure. The overall sample was divided into subsamples with (n = 75) and without (n = 138) cognitive processing speed impairment based on normative Symbol-Digit Modalities Test data. Correlations between SSST performance with other mobility outcomes in the overall sample and cognitive processing speed impairment subsamples were examined and compared. SSST performance was compared relative to other mobility measures for differentiating MS walking function levels in people with and without cognitive processing speed impairment.

RESULTS

SSST performance was significantly and strongly correlated with most mobility outcomes in the overall sample and cognitive processing speed impairment subsamples. The magnitudes of correlations between SSST performance with most mobility outcomes were not statistically different among subsamples. Cognitive processing speed impairment did not diminish the relative precision of SSST performance for differentiating walking function levels.

CONCLUSION

The presence of cognitive processing speed impairment is not a source of invalidity or imprecision when interpreting SSST performance as a functional mobility measure among people with MS.

IMPACT

The SSST is a high-quality endpoint for inclusion in interventions targeting mobility in MS, regardless of cognitive processing speed status. This information is critical for rehabilitation research and clinical practice given that mobility and cognitive impairment are highly prevalent, co-occurring, and disabling in MS.