The dominant clinical tool used to track multiple sclerosis disability — a motor-focused number that tells clinicians how well a patient can walk — consistently fails to capture MS cognitive impairment prevalence, affecting an estimated 40 to 65 percent of people with MS, and a 223-study synthesis of 300,911 patients now provides the largest quantitative case for changing that. Published in Neuropsychology Review on October 19, 2026, the synthesis found moderate but statistically robust negative correlations between physical disability scores and performance on three established cognitive tests — correlations that strengthen as disease advances — establishing that physical and cognitive impairment in MS co-travel as expressions of a shared neurobiological process rather than running on separate tracks, as MS News Today reported.

The finding is not surprising to MS neurologists; it is large. No prior quantitative review of the physical-cognitive disability relationship in MS has brought together 223 studies and more than 300,000 patients under a unified analytical framework, according to meta-analysis authors at Neuropsychology Review. That scale gives the correlations a statistical authority that earlier, smaller, inconsistent studies could not provide — and it gives clinicians who have advocated for routine cognitive screening a firm evidential foundation.

300,911 Patients, Three Cognitive Tests, One Direction

Led by Omid Mirmosayyeb and colleagues — with Elham Moases Ghaffary of the University of Missouri-Kansas City as corresponding author — the team screened 16,340 records from a literature search covering studies up to August 2024, ultimately including 223 studies in the review. Of those, 93 contained data suitable for formal meta-analysis, in which correlation coefficients were pooled using random-effects models to account for the heterogeneity inherent in studies of this scope.

The patient population had a mean age of 46.4 years, was 72 percent female, and had lived with MS for a mean of 9.2 years. The mean Expanded Disability Status Scale (EDSS) score was 2.2 — indicating mild disability with no walking impairment — making this a sample weighted toward earlier disease stages.

Physical disability was assessed primarily through the EDSS. Cognitive performance was captured through three tests: the Symbol Digit Modalities Test (SDMT), which gauges information-processing speed; the Mini-Mental State Examination (MMSE); and the Montreal Cognitive Assessment (MoCA). Pooling data across studies, researchers found moderate, statistically significant correlations between EDSS scores and cognitive performance across all three instruments:

• EDSS-to-SDMT correlation coefficient: −0.42
• EDSS-to-MMSE: −0.46
• EDSS-to-MoCA: −0.43

In every case: higher physical disability, worse cognitive performance. Sensitivity analyses confirmed the robustness of these results, and formal tests for publication bias found it to be minimal.

The single largest component of the analysis — the EDSS-SDMT relationship — pooled data from 65 studies involving 7,823 patients, giving the correlation estimate considerable statistical weight.

The associations extended beyond physician-administered scores. Poorer SDMT performance was also significantly linked to worse performance on the 9-Hole Peg Test (9HPT), a measure of hand dexterity (r = −0.34); the Timed 25-Foot Walk Test (T25FW), a standard ambulation measure (r = −0.23); and the Patient-Determined Disease Steps (PDDS), a patient-reported disability scale (r = −0.28). Across every physical functional measure examined, the pattern held.

Cognitive Burden Intensifies at Higher Disability Levels — But Appears Earlier

The most clinically consequential finding is what happened when the team stratified by EDSS severity. Subgroup analyses showed the correlation between physical disability and cognitive impairment was substantially stronger in patients with higher EDSS scores — more advanced disease — than in those with milder physical impairment, per the pooled subgroup analysis.

But the relationship does not materialize only at advanced stages. The data also establish that cognitive difficulties can and do emerge in patients with relatively preserved mobility — in a pattern the EDSS would not capture or flag. Someone experiencing significant problems with memory, attention, or information-processing speed may still receive a low disability score if their walking is intact.

“Although it has a high prevalence and significant impact, cognitive function is poorly captured by conventional disability rating scales in PwMS,” the researchers wrote in Neuropsychology Review, noting that the EDSS’s motor-centric design “leads to an inaccurate representation of their overall disability burden.”

Three variables that might plausibly moderate the physical-cognitive relationship — age, disease duration, and MS subtype — were not significant moderators in the analysis. That null finding is itself informative: the interdependence of physical and cognitive disability appears to be a feature of MS as a whole, not specific to particular patient ages, years since diagnosis, or clinical forms such as relapsing-remitting versus progressive MS.

What the EDSS Was Designed to Measure — and What It Was Not

The EDSS was developed by neurologist John Kurtzke in 1983 and has anchored MS clinical trials and disability assessments ever since. Its longevity reflects genuine utility: it is reproducible, widely understood, and directly linked to the outcomes patients and clinicians care about most. But its architecture reflects the clinical thinking of its era. Built around motor and functional systems — walking speed and distance, balance, limb coordination — the EDSS assigns no formal cognitive score until extreme stages.

Inter-rater reliability for the EDSS is moderate, with reported kappa values ranging from 0.32 to 0.76 depending on the clinical context — a known limitation that adds noise to longitudinal disability tracking.

This design has always coexisted uneasily with the epidemiology of MS cognition. Cognitive impairment can emerge early in the disease — sometimes as one of its first visible manifestations. Information-processing speed, working memory, verbal learning, and executive function are the domains most commonly compromised, and they are the domains that determine whether someone can hold a job, manage medications, follow a conversation, or drive safely. By those measures, cognitive impairment can constitute the most disabling aspect of MS for many patients whose EDSS scores suggest mild disease.

MS neurology researcher Mark Gudesblatt, MD, presented data at ECTRIMS confirming that cognitive function “does not impact EDSS” — that the two systems are assessed independently — in 258 MS patients tested with NeuroTrax, where global cognitive scores overlapped only roughly 42.5 percent between the extremes of EDSS groups.

How Motor and Cognitive Disability Share the Same Neurobiological Roots

Why does physical disability track with cognitive impairment, without one causing the other? The answer lies in what MS is doing to the brain.

MS damages the central nervous system through two interlocking processes operating in parallel. The first is inflammatory lesions — focal white matter lesion damage, affecting myelin and axons acutely. These affect both motor pathways (the corticospinal tract, cerebellar connections) and cognitive networks (the corpus callosum, fronto-striatal projections, hippocampal and temporal lobe circuitry). The second process is progressive neurodegeneration: global axonal and neuronal loss — brain atrophy — that accumulates regardless of visible inflammatory activity and advances in parallel across motor and cognitive systems.

Accumulating evidence from neuroimaging research suggests that global brain atrophy is a stronger predictor of both motor and cognitive outcomes in MS than focal lesion counts alone — because atrophy reflects the total disease burden affecting all neural systems simultaneously. Motor pathways running through the corticospinal tract and cerebellum determine much of the EDSS score. Cognitive networks are more diffusely organized: information-processing speed depends on fronto-striatal and callosal connections; memory relies on hippocampal and temporal lobe circuitry; executive function draws on prefrontal and parietal areas.

This shared-substrate biology explains both the moderate correlation (same damaging process) and the imperfect correlation (distinct anatomical targets). As overall disease burden increases — higher EDSS — the atrophic process is more advanced, and cognitive damage is more extensive. Prior research from the EXPAND clinical trial database found that in secondary-progressive MS patients, the worst cognitive processing speed scores were associated with nearly double the likelihood of wheelchair dependence compared to the best cognitive performers — a finding that now sits within the larger quantitative context established by this meta-analysis.

Existing Tools for Cognitive Screening Exist — and Are Underused

The study’s findings are not a demand for new instrumentation. Validated cognitive screening tools already exist and are already used in many MS specialty centers; they are simply not universally deployed in routine clinical care.

The Symbol Digit Modalities Test (SDMT) — the cognitive measure with the most data in this meta-analysis — is a brief, validated test of information-processing speed that takes roughly 90 seconds to administer orally and is sensitive to MS cognitive change. The Brief International Cognitive Assessment for MS (BICAMS), a 15-minute battery validated across more than 35 countries and languages, has been recommended as a routine screening tool by MS clinical guidelines in multiple countries but remains inconsistently deployed in practice.

The Multiple Sclerosis Functional Composite (MSFC), which includes a cognitive component, has been validated as a trial endpoint but has not displaced the EDSS in routine clinical practice.

The authors recommend that cognitive assessment be included in regular evaluations, with particular attention to early disease stages — where cognitive impairment may precede or outpace motor signs — and call for “redefining MS disability in a multidimensional framework, integrating cognition, fatigue, and upper limb function with traditional mobility measures,” according to the Neuropsychology Review paper.

MS Drug Trials Risk Missing Cognitive Benefit — or Cognitive Harm

The implications of the study’s findings extend beyond the clinic into the MS pharmaceutical pipeline, and they cut both ways.

Clinical trials that use EDSS change as their primary disability endpoint — the current regulatory standard accepted by the FDA and European Medicines Agency — are not powered to detect cognitive improvement or cognitive decline as distinct outcomes. A trial testing a neuroprotective or remyelinating therapy whose mechanism of action preferentially spares cognitive networks could show no statistically significant EDSS benefit while producing meaningful cognitive benefit for patients — and that benefit would be invisible to the trial’s primary endpoint.

The same gap operates in reverse: a therapy that slows motor disability progression while producing cognitive side effects might pass a regulatory threshold based on EDSS improvement while impairing the cognitive function that many MS patients identify as their most disabling symptom.

This is not a theoretical concern. Prior meta-analysis research in the Annals of Clinical and Translational Neurology found that cognitive decline worsens progressively across the clinically isolated syndrome–RRMS–PPMS–SPMS axis, independent of physical disability staging — reinforcing that cognitive impairment is a core feature of MS disease biology, not a secondary consequence of motor limitations. The 2026 Mirmosayyeb synthesis now adds the population-scale quantitative backbone.

For MS clinical trialists, this data adds to growing pressure to include cognitive endpoints — particularly the SDMT — as co-primary outcomes in neuroprotective and remyelinating therapy trials.

Limitations of What a Correlation Analysis Can Establish

The researchers were careful to define what their pooled analysis can and cannot establish. The studies included varied widely in cognitive instruments, study design, and participant selection — sources of methodological heterogeneity the authors acknowledge throughout their paper.

More importantly, key confounders that independently affect both cognitive performance and physical disability — depression, fatigue, sleep disturbance, medication burden — were not consistently reported across included studies and could not be controlled for in the pooled analyses.

“Therefore, it must be acknowledged that the correlations found may not reflect a direct relationship between physical and cognitive disability,” the authors wrote. The association is real and robust; whether one drives the other, or whether both are downstream of shared neurobiological processes such as white matter lesion burden and brain atrophy, cannot be resolved by correlation-based synthesis alone.

The cross-sectional nature of most included studies also prevents inference about the temporal relationship: does motor disability lead to cognitive decline, does cognitive decline hasten motor disability progression, or do the two simply co-vary as expressions of the same underlying pathology? Longitudinal studies with parallel motor and cognitive tracking — ideally with neuroimaging endpoints — will be needed to answer that question.

What This Means for People Living With MS

For the 3.1 million people worldwide with MS, this meta-analysis confirms something many have reported but seen inadequately reflected in their clinical records: the cognitive experience of the disease — difficulty concentrating, word-finding lapses, slowed processing that makes a conversation or a workday feel exhausting — is not separate from its physical progression but interwoven with it, across the full spectrum of disability.

Cognitive impairment predicts employment loss and is among the strongest predictors of reduced function in MS. A patient with an EDSS score of 2 — mild disability, walking unimpaired — who is losing their ability to process information quickly enough to function in their job has a disability that their clinical record does not record.

For neurologists and MS nurses conducting routine follow-up visits, the results reinforce the case for incorporating validated brief cognitive screening — the SDMT or BICAMS — into standard disability assessments regardless of a patient’s EDSS score. For healthcare systems and payers, earlier cognitive screening supports earlier vocational intervention, workplace accommodation, and neuropsychological rehabilitation. The study cannot yet say how much earlier detection of cognitive decline would change outcomes. The first step is measuring it.

Frequently Asked Questions

Does having a low EDSS score mean my cognitive function is normal?

No. The EDSS measures walking ability and motor function; it was not designed to assess cognition. This meta-analysis found moderate negative correlations between EDSS scores and cognitive test performance across 300,911 patients — meaning that patients with low EDSS scores (mild physical disability) can still experience significant cognitive impairment. If you have MS and are concerned about memory, attention, word-finding, or processing speed, ask your neurologist for a cognitive screening test such as the SDMT or BICAMS regardless of your EDSS score. Details are in the Neuropsychology Review meta-analysis.

What specific cognitive tests can detect MS-related cognitive impairment that the EDSS misses?

The Symbol Digit Modalities Test (SDMT) is the most studied and most sensitive brief tool for MS cognitive impairment, taking roughly 90 seconds to administer orally. The BICAMS brief assessment battery is a 15-minute test validated in more than 35 countries. The Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE) are general-purpose screeners also examined in this meta-analysis. A validated SDMT reference guide explains its administration and scoring in the MS context. Any of these can be administered at routine MS appointments and provide cognitive data that an EDSS assessment does not capture.

What does this meta-analysis mean for MS drug trials and future treatments?

Most MS clinical trials use EDSS change as their primary disability endpoint — the standard accepted by the FDA and European Medicines Agency for drug approval. Because the EDSS does not measure cognition, a neuroprotective therapy that preserves or improves cognitive function without dramatically changing walking ability might show no EDSS benefit and fail regulatory review, even if it delivers meaningful gains for patients in their daily lives. This meta-analysis adds to the evidence base that cognitive endpoints — particularly the SDMT — should be included as co-primary outcomes in neuroprotective and remyelinating therapy trials. That regulatory shift, if it occurs, could change which treatments reach approval and how MS drug development is designed.

Why is cognitive impairment so common in MS, and why does it worsen alongside physical disability?

MS damages the central nervous system through inflammatory lesions and progressive brain atrophy — processes that affect both the motor pathways that determine EDSS scores and the cognitive networks that govern processing speed, memory, and executive function. Both types of damage stem from the same underlying MS disease biology: white matter lesion burden and whole-brain atrophy advance in parallel across motor and cognitive systems, which is why physical and cognitive disability track together even though they are anatomically distinct. This shared-substrate biology explains the moderate correlation (same disease, same process) and the imperfect correlation (different neural targets) found in the Neuropsychology Review meta-analysis.

The paper, “Cognitive Function and Disability in People with Multiple Sclerosis: A Systematic Review and Meta-Analysis,” by Omid Mirmosayyeb, Mohammad Yazdan Panah, Shahryar Rajai Firouzabadi, Ida Mohammadi, Mohammadreza Alinejadfard, Saeed Vaheb, Vahid Shaygannejad, Elham Moases Ghaffary, and co-authors, is published in Neuropsychology Review (doi: 10.1007/s11065-026-09706-9; published online October 19, 2026).