Anne Haney Cross

Central nervous system injury causes motor deficits through derangement of excitatory, inhibitory, and/or neuromodulatory inputs to motoneurons, the three fundamental components of motor commands. Typically, study of pathologic neural control in humans is restricted to only one of the three. Chardon et al. (2024) presented a fundamentally new approach to comprehensively study all components by reverse engineering motor unit firing patterns. We apply their framework to motor unit firing patterns from 89 people with multiple sclerosis (MS) and 34 controls to study excitatory, inhibitory, and neuromodulatory contributions to pathologic motor output. Disruptions to all components are plausible in MS, a disease hallmarked by heterogeneity in nearly all aspects. Accordingly, we found abnormalities in MS for all three components. Notably, neuromodulation included both high and low extremes. Our results suggest that pathophysiology of motor commands in MS varies among patients, a finding fundamentally different from other studied populations showing relative consistency.

Oral cladribine tablet (CladT) therapy is efficacious for relapsing multiple sclerosis (MS). However, the mechanisms by which cladribine exerts benefit in MS remain unclear, particularly regarding its effects on compartmentalized inflammation within the CSF. Transcriptional profiles along with T and B lymphocyte receptor repertoires from CSF and blood were obtained by single-cell sequencing methods from a single site participating in a phase IV clinical trial investigating the impact of cladribine treatment for MS. Blood and CSF samples from patients were obtained immediately before starting CladT therapy, and they were randomized to also provide additional samples at either 5 weeks, 10 weeks, 1 year, or 2 years after CladT therapy. Thirty-four samples from 13 individuals with relapsing MS before and after treatment were available to test the hypothesis that CladT alters the composition and phenotype of lymphocytes in the CSF, including paired baseline and post-CladT CSF samples obtained from 4 unique participants. We found that treatment with CladT profoundly altered cellular composition, but not the transcriptional phenotype, of immune cells in the CSF. In particular, we identified a reduction in switched memory B cells but recovery of naive B cells in the CSF, similar to our findings in blood. In addition, populations of CD4 Treg cells emerged early after CladT therapy and remained elevated 1 year later in the CSF, but not in the blood. Antigen receptor sequencing revealed a moderate decrease in numbers of large clonally expanded CD8 T cell clones (>10 cells/clone) primarily in the CSF, but also in the blood after CladT treatment. Our results identified unique cellular dynamics and changes in T cell and B cell clonality in both tissues, which can potentially explain long-term beneficial effects of CladT therapy in MS, including preservation of immune function and a relatively low number of side effects. Altogether, this study demonstrates that CladT treatment had a substantial impact not only on blood but also on the CSF compartment, highlighting the importance of cross-tissue analysis for better understanding of effect and the mechanism of action of disease-modifying therapies.

Objective: The growing demand for personalized treatment in multiple sclerosis (MS) highlights the need for more precise biomarkers that can outperform magnetic resonance imaging and clinical assessment in patient stratification. Advances in multiplex proteomic technologies suggest that cerebrospinal fluid (CSF) analysis at MS onset may not only improve diagnostic accuracy, but also offer prognostic and staging information, as well as insight into molecular therapeutic targets. Methods: This multicenter study retrospectively analyzed cryopreserved CSF samples from 160 individuals undergoing diagnostic evaluation for possible neuroimmunological disorder, and among these, followed a cohort of 96 people with confirmed MS for at least 3 years. The goal was to externally validate previously published CSF‐based diagnostic and prognostic classifiers. Results: Upon unblinding, the CSF‐based molecular diagnostic test distinguished 96 people with confirmed MS from 30 individuals with other inflammatory neurological diseases, and 34 individuals with non‐inflammatory neurological diseases, achieving an area under the receiver operating characteristic curve of 0.94 ( p = 4.7 × 10 ⁻²¹ ). The test also differentiated 65 individuals with relapsing–remitting MS from 31 individuals with progressive MS, with an area under the receiver operating characteristic curve of 0.76 ( p = 1.4 × 10 ⁻⁵ ). The prognostic classifier predicted prospectively measured Expanded Disability Status Scale scores at follow up (rho = 0.43, p = 2.54 × 10 ⁻⁵ ). Interpretation: This multicenter external validation study demonstrates that CSF‐based molecular tests can robustly distinguish MS from other neurological conditions, stratify MS subtypes, and predict future disability progression in real‐world settings. These results lay the groundwork for development of next‐generation molecular tools to personalize care in MS. ANN NEUROL 2026;99:328–340

Multiple sclerosis (MS) is a progressive inflammatory neurodegenerative disease that degrades neural transmission between the brain and spinal α-motoneurons. These voluntary motor commands contain excitatory, inhibitory, and neuromodulatory components that must be appropriately balanced for skilled motor control. Unlike other clinical populations, in MS we have no knowledge about how voluntary motor commands are disrupted. MS is a clinically heterogeneous population, with sensorimotor impairments that vary widely and unpredictably across patients. Our overall scientific hypothesis is that the voluntary motor command in the MS population varies accordingly, with multiple “phenotypes” evident. Here, we explore this idea by identifying pathological aspects of the voluntary motor command in 59 participants with MS with a range of sensorimotor symptoms and disability, compared with 38 age-/sex-matched controls. We recorded motor unit discharge from the tibialis anterior and soleus muscles during isometric dorsiflexion/plantarflexion contractions. We then calculated geometric and temporal features in their firing patterns to characterize their excitatory, inhibitory, and neuromodulatory inputs according to a recently developed “reverse engineering” paradigm. MS values for many of our parameters were highly variable, with some participants with abnormally values and others with abnormally low values. In addition to this variability, MS group means for most parameters reflecting the balance of neuromodulation and inhibition were significantly lower than those of controls. These initial findings support the idea that there may be different phenotypes of voluntary motor command pathology among patients with MS, indicating the potential need to personalize the selection of mechanistically targeted rehabilitation therapies.

Objective: The claustrum is a small, thin structure of predominantly gray matter with broad connectivity and enigmatic function. Little is known regarding the impact of claustrum pathology in multiple sclerosis (MS).Methods: This study assessed whether claustrum volume was reduced in MS and whether reductions were associated with specific disability domains. We compared the impact of claustrum volume reductions on neurological disability versus the well‐studied thalamus. Data from the 15,793 participants in the MS PATHS study were used for primary analyses. A second cohort of 71 people with MS and healthy controls from our center was used for validation.Results: Claustrum and thalamic volumes were reduced to a similar degree across MS types. Claustrum volume, like thalamic volume, was associated with disability measures of walking speed, upper extremity dexterity, and cognition. Partial correlation analyses supported that both claustrum and thalamic volumes independently contribute to disability. Interestingly, claustrum volume outperformed thalamic volume as a predictor of future disability progression.Interpretation: This study suggests that damage and resulting atrophy to the claustrum may be an important component of MS‐related disability.

Single-cell transcriptomics applied to cerebrospinal fluid (CSF) for elucidating the pathophysiology of neurologic diseases has produced only a preliminary characterization of CSF immune cells. CSF derives from and borders central nervous system (CNS) tissue, allowing for comprehensive accounting of cell types along with their relative abundance and immunologic profiles relevant to CNS diseases. Using integration techniques applied to publicly available datasets in combination with our own studies, we generated a compendium with 139 subjects encompassing 135 CSF and 58 blood samples. Healthy subjects and individuals across a wide range of diseases, such as multiple sclerosis (MS), Alzheimer’s disease, Parkinson’s disease, COVID-19, and autoimmune encephalitis, were included. We found differences in lymphocyte and myeloid subset frequencies across different diseases as well as in their distribution between blood and CSF. We identified what we believe to be a new subset of AREG ⁺ dendritic cells exclusive to the CSF that was more abundant in subjects with MS compared with healthy controls. Finally, transcriptional cell states in CSF microglia-like cells and lymphoid subsets were elucidated. Altogether, we have created a reference compendium for single-cell transcriptional profiling encompassing CSF immune cells useful to the scientific community for future studies on neurologic diseases.

Objective: Despite treatments which reduce relapses in multiple sclerosis (MS), many patients continue to experience progressive disability accumulation. MS is associated with metabolic disruptions and cerebral metabolic stress predisposes to tissue injury and possibly impaired remyelination. Additionally, myelin homeostasis is metabolically expensive and reliant on glycolysis. We investigated cerebral metabolic changes in MS and when in the disease course they occurred, and assessed their relationship with microstructural changes.Methods: This study used combined fluorodeoxyglucose (FDG) positron emission tomography (PET) and magnetic resonance imaging (MRI) to measure cerebral metabolic rate of glucose and oxygen, thereby quantifying glycolysis. Twelve healthy controls, 20 patients with relapsing MS, and 13 patients with non‐relapsing MS were studied. Relapsing patients with MS were treatment naïve and scanned pre‐ and post‐initiation of high efficacy disease modifying therapy.Results: In normal appearing white matter, we observed increased glucose utilization and reduced oxygen utilization in newly diagnosed MS, consistent with increased glycolysis. Increased glycolysis was greater in patients with a longer disease duration course and higher disability. Among newly diagnosed patients, different treatments had differential impacts on glucose utilization. Last, whereas hypermetabolism within lesions was clearly associated with inflammation, no such relationship was found within normal appearing white matter.Interpretation: Increased white matter glycolysis is a prominent feature of cerebral metabolism in MS. It begins early in the disease course, increases with disease duration and is independent of microstructural evidence of inflammation in normal appearing white matter. Optimization of the metabolic environment may be an important component of therapies designed to reduce progressive disability. ANN NEUROL 2025;97:766–778

Background: Calorie restriction (CR) ameliorates preclinical models of multiple sclerosis (MS) via multiple mechanisms. These include decreased leptin, a proinflammatory adipokine, but mechanistic studies in humans are lacking. Tests of daily and intermittent CR (iCR) in people with MS (pwMS) showed improvements in fatigue and well-being measures. This trial studied the effects of 12-week iCR on metabolic, immunological, and clinical outcomes in pwMS.Method: Relapsing-remitting MS participants were randomised to iCR or a control group. Study visits were conducted at baseline, 6 and 12 weeks. The primary outcome was reduction in serum leptin levels at 12 weeks. Feasibility and safety were assessed by diet adherence and adverse events (AEs). Secondary outcomes included changes in anthropometric and body composition measures, metabolic and immunologic profiling, and clinical measures. Mixed effects linear regression models were used to evaluate outcome differences between and within groups over time.Results: Forty-two pwMS were randomised, 34 completed the study (17/group). Leptin serum levels at 12 weeks were significantly lower in the iCR versus the control group (mean decrease −6.98 µg/dL, 95% CI: −28.02 to 14.06; p=0.03). Adherence to iCR was 99.5% and 97.2% at 6 and 12 weeks, respectively, and no serious AEs were reported. An increase in blood CD45RO⁺regulatory T-cell numbers was seen after 6 weeks of iCR. Exploratory cognitive testing demonstrated a significant improvement in the Symbol Digit Modality Test Score in the iCR group at 12 weeks.Conclusions: iCR has the potential to benefit metabolic and immunologic profiles and is safe and feasible in pwMS.Trial registration number: NCT03539094.