Occurrence of neuronal dysfunction during the first 5 years of multiple sclerosis is associated with cognitive deterioration

Symptom Interconnectivity in Multiple Sclerosis: A Narrative Review of Potential Underlying Biological Disease Processes

Introduction

Fatigue, cognitive impairment, depression, and pain are highly prevalent symptoms in multiple sclerosis (MS). These often co-occur and may be explained by a common etiology. By reviewing existing literature, we aimed to identify potential underlying biological processes implicated in the interconnectivity between these symptoms.

Methods

A literature search was conducted to identify articles reporting research into the biological mechanisms responsible for the manifestation of fatigue, cognitive impairment, depression, and pain in MS. PubMed was used to search for articles published from July 2011 to July 2021. We reviewed and assessed findings from the literature to identify biological processes common to the symptoms of interest.

Results

Of 693 articles identified from the search, 252 were selected following screening of titles and abstracts and assessing reference lists of review articles. Four biological processes linked with two or more of the symptoms of interest were frequently identified from the literature: (1) direct neuroanatomical changes to brain regions linked with symptoms of interest (e.g., thalamic injury associated with cognitive impairment, fatigue, and depression), (2) pro-inflammatory cytokines associated with so-called ‘sickness behavior,’ including manifestation of fatigue, transient cognitive impairment, depression, and pain, (3) dysregulation of monoaminergic pathways leading to depressive symptoms and fatigue, and (4) hyperactivity of the hypothalamic–pituitary-adrenal (HPA) axis as a result of pro-inflammatory cytokines promoting the release of brain noradrenaline, serotonin, and tryptophan, which is associated with symptoms of depression and cognitive impairment.

Conclusion

The co-occurrence of fatigue, cognitive impairment, depression, and pain in MS appears to be associated with a common set of etiological factors, namely neuroanatomical changes, pro-inflammatory cytokines, dysregulation of monoaminergic pathways, and a hyperactive HPA axis. This association of symptoms and biological processes has important implications for disease management strategies and, eventually, could help find a common therapeutic pathway that will impact both inflammation and neuroprotection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-022-00368-2.

Identifying Early Neuropsychological Indicators of Cognitive Involvement in Multiple Sclerosis

Multiple sclerosis (MS) is a debilitating disease of the central nervous system that is most commonly seen in early to middle adulthood, although it can be diagnosed during childhood or later in life. While cognitive impairment can become more prevalent and severe as the disease progresses, signs of cognitive involvement can be apparent in the early stages of the disease. In this review, we discuss the prevalence and types of cognitive impairment seen in early MS, including the specific measures used to identify them, as well as the challenges in characterizing their frequency and progression. In addition to examining the progression of early cognitive involvement over time, we explore the clinical factors associated with early cognitive involvement, including demographics, level of physical disability, disease modifying therapy use, vocational status, and psychological and physical symptoms. Given the prevalence and functional impact these impairments can have for persons with MS, considerations for clinicians are provided, such as the role of early cognitive screenings and the importance of comprehensive neuropsychological assessments.

Impact of Pharmacotherapy on Cognitive Dysfunction in Patients with Multiple Sclerosis

Cognitive impairment is a common symptom of multiple sclerosis (MS), adversely impacting many spheres of daily functioning. Yet the effectiveness of pharmacological interventions for cognitive impairment in MS is unclear. Clinicians and patients alike would benefit from formal guidelines regarding effective management of cognitive symptoms. We reviewed the background on the measurement, pathophysiology and risk factors for cognitive dysfunction in MS, and then examined the published clinical trials of pharmacotherapy, including both disease-modifying treatments (DMTs) and symptom-management therapies (SMTs). Our review of DMTs revealed only a single well-designed, randomized, controlled trial where intramuscular interferon (IFN)-β1a, administered once weekly, was compared with placebo. The results showed significant benefits in terms of cognitive processing speed and memory. Less convincing but promising data have shown the potential benefits of IFN-β1b and natalizumab. The literature on SMTs is replete with placebo-controlled, single-centre studies, with a failure to replicate initially promising results. The results for SMTs such as acetylcholinesterase inhibitors and psychostimulants are mixed. Some encouraging data show promise but not to a threshold of indication for standard clinical use. Numerous methodological factors hamper research in this area. Acknowledging the lack of firm conclusions, we argue that all DMTs are likely to benefit cognition and that, if otherwise safe, SMTs with some empirical support may be attempted at the discretion of the treating clinician. We offer some guidance on the assessment and monitoring of cognitive function to inform off-license treatment of cognitive impairment in MS patients.

Stable neuropsychiatric status in multiple sclerosis: a 3-year study

Personality changes and neuropsychiatric symptoms are found in multiple sclerosis (MS), but no study has evaluated decline compared to healthy controls. This study assessed personality traits and neuropsychiatric symptoms over 3 years using the NEO Five Factor Inventory and the Neuropsychiatric Inventory. Additional metrics evaluated ambulation, manual dexterity and cognitive function. Contrary to hypothesis, patients showed no significant change in personality or neuropsychiatric status relative to controls. Patients were impaired in motor and cognitive function at baseline and follow-up, but showed only slowing in ambulation over time. The findings indicate that neuropsychiatric status is stable in MS over 3 years.

Symptomatic treatment and management of multiple sclerosis

The range of symptoms which occur in multiple sclerosis (MS) can have disabling functional consequences for patients and lead to significant reductions in their quality of life. MS symptoms can also interact with each other, making their management challenging. Clinical trials aimed at identifying symptomatic therapies have generally been poorly designed and have tended to be underpowered. Therefore, the evidence base for the management of MS symptoms with pharmacologic therapies is not strong and tends to rely upon open-label studies, case reports, and clinical trials with small numbers of patients and poorly validated clinical outcome measures. Recently, there has been a growing interest in the management of MS symptoms with pharmacologic treatments, and better-designed, randomized, double-blind, controlled trials have been reported. This chapter will describe the evidence base predominantly behind the various pharmacologic approaches to the management of MS symptoms, which in most, if not all, cases, requires multidisciplinary input. Drugs routinely recommended for individual symptoms and new therapies, which are currently in the development pipeline, will be reviewed. More interventional therapies related to symptoms that are refractory to pharmacotherapy will also be discussed, where relevant.

Serial proton MR spectroscopy of gray and white matter in relapsing-remitting MS

OBJECTIVE

To characterize and follow the diffuse gray and white matter (GM/WM) metabolic abnormalities in early relapsing-remitting multiple sclerosis using proton magnetic resonance spectroscopic imaging ((1)H-MRSI).

METHODS

Eighteen recently diagnosed, mildly disabled patients (mean baseline time from diagnosis 32 months, mean Expanded Disability Status Scale [EDSS] score 1.3), all on immunomodulatory medication, were scanned semiannually for 3 years with T1-weighted and T2-weighted MRI and 3D (1)H-MRSI at 3 T. Ten sex- and age-matched controls were followed annually. Global absolute concentrations of N-acetylaspartate (NAA), choline (Cho), creatine (Cr), and myo-inositol (mI) were obtained for all GM and WM in the 360 cm(3) (1)H-MRSI volume of interest.

RESULTS

Patients' average WM Cr, Cho, and mI concentrations (over all time points), 5.3 ± 0.4, 1.6 ± 0.1, and 5.1 ± 0.7 mM, were 8%, 12%, and 11% higher than controls' (p ≤ 0.01), while their WM NAA, 7.4 ± 0.7 mM, was 6% lower (p = 0.07). There were increases with time of patients' WM Cr: 0.1 mM/year, Cho: 0.02 mM/year, and NAA: 0.1 mM/year (all p < 0.05). None of the patients' metabolic concentrations correlated with their EDSS score, relapse rate, GM/WM/CSF fractions, or lesion volume.

CONCLUSIONS

Diffuse WM glial abnormalities were larger in magnitude than the axonal abnormalities and increased over time independently of conventional clinical or imaging metrics and despite immunomodulatory treatment. In contrast, the axonal abnormalities showed partial recovery, suggesting that patients' lower WM NAA levels represented a dysfunction, which may abate with treatment. Absence of detectable diffuse changes in GM suggests that injury there is minimal, focal, or heterogeneous between cortex and deep GM nuclei.

An overview of the association between gray matter damage and cognitive impairment in multiple sclerosis

SUMMARY In multiple sclerosis (MS), cognitive impairment can be present in up to 70% of patients. Although pathological processes underlying cognitive impairment are complex, there is growing evidence that gray matter (GM) damage plays a crucial role in determining cognitive dysfunction. All forms of GM damage, namely GM volume loss, damage in the normal-appearing GM and cortical lesions have been found to be related to cognitive decline in patients with MS. GM can also be involved in cognitive impairment in the context of cortical reorganization, which is probably an adaptive phenomenon, the failure of which has been reported to be associated with cognitive impairment. In this review, the evidence for the involvement of GM damage in cognitive impairment in MS and the future directions of research are discussed.

Metabolic profile of PML lesions in patients with and without IRIS: an observational study

OBJECTIVE

To characterize progressive multifocal leukoencephalopathy (PML) lesions by contrast-enhanced MRI and evaluate their metabolism using proton magnetic resonance spectroscopy ((1)H- MRS) in the setting of immune reconstitution inflammatory syndrome (IRIS).

METHODS

A total of 42 patients with PML underwent a clinical evaluation as well as brain MRI and (1)H-MRS at baseline and 3, 6, and 12 months later. The presence of IRIS was determined based on clinical and laboratory criteria. Ratios of N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), and lipid/lactate (Lip1 and Lip2) to creatine (Cr) were measured and correlated with the presence of contrast enhancement (CE) in PML lesions.

RESULTS

IRIS occurred in 16 of 28 (57.1%) PML survivors (PML-S) and 1 of 14 (7.1%) PML progressors (PML-P). Lesions of patients with PML-IRIS showed significantly higher Cho/Cr (p = 0.0001), mI/Cr (p = 0.02), Lip1/Cr (p < 0.0001), and Lip2/Cr (p = 0.002) ratios and lower NAA/Cr (p = 0.02) ratios than patients with PML who did not have IRIS. An elevated Cho/Cr ratio was associated with CE within the (1)H-MRS voxel, whereas lipid/Cr ratios were elevated in PML-IRIS lesions independently of CE. Follow-up until 33 months from PML onset showed persistent elevation of the mI/Cr ratio in lesions of patients with PML-IRIS. A Lip1/Cr ratio greater than 1.5 combined with the presence of CE yielded a 79% probability of IRIS compared with 13% in the absence of these criteria.

CONCLUSION

(1)H-MRS is a valuable tool to recognize and track IRIS in PML and may prove useful in the clinical management of these patients.

Voxelwise analysis of conventional magnetic resonance imaging to predict future disability in early relapsing–remitting multiple sclerosis

Background:

The ability of conventional magnetic resonance imaging (MRI) to predict subsequent physical disability and cognitive deterioration after a clinically isolated syndrome (CIS) is weak.

Objectives:

We aimed to investigate whether conventional MRI changes over 1 year could predict cognitive and physical disability 5 years later in CIS. We performed analyses using a global approach (T2 lesion load, number of T2 lesions), but also a topographic approach.

Methods:

This study included 38 patients with a CIS. At inclusion, 10 out of 38 patients fulfilled the 2010 revised McDonald’s criteria for the diagnosis of multiple sclerosis. Expanded Disability Status Scale (EDSS) evaluation was performed at baseline, year 1 and year 5, and cognitive evaluation at baseline and year 5. T2-weighted MRI was performed at baseline and year 1. We used voxelwise analysis to analyse the predictive value of lesions location for subsequent disability.

Results:

Using the global approach, no correlation was found between MRI and clinical data. The occurrence or growth of new lesions in the brainstem was correlated with EDSS changes over the 5 years of follow-up. The occurrence or growth of new lesions in cerebellum, thalami, corpus callosum and frontal lobes over 1 year was correlated with cognitive impairment at 5 years.

Conclusion:

The assessment of lesion location at the first stage of multiple sclerosis may be of value to predict future clinical disability.

IFN-gamma signaling in the central nervous system controls the course of experimental autoimmune encephalomyelitis independently of the localization and composition of inflammatory foci

Background

Murine experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, presents typically as ascending paralysis. However, in mice in which interferon-gamma (IFNγ) signaling is disrupted by genetic deletion, limb paralysis is accompanied by atypical deficits, including head tilt, postural imbalance, and circling, consistent with cerebellar/vestibular dysfunction. This was previously attributed to intense cerebellar and brainstem infiltration by peripheral immune cells and formation of neutrophil-rich foci within the CNS. However, the exact mechanism by which IFNγ signaling prohibits the development of vestibular deficits, and whether the distribution and composition of inflammatory foci within the CNS affects the course of atypical EAE remains elusive.

Methods

We induced EAE in IFNγ-/- mice and bone marrow chimeric mice in which IFNγR is not expressed in the CNS but is intact in the periphery (IFNγR^CNSKO) and vice versa (IFNγR^periKO). Blood-brain barrier permeability was determined by Evans blue intravenous administration at disease onset. Populations of immune cell subsets in the periphery and the CNS were quantified by flow cytometry. CNS tissues isolated at various time points after EAE induction, were analyzed by immunohistochemistry for composition of inflammatory foci and patterns of axonal degeneration.

Results

Incidence and severity of atypical EAE were more pronounced in IFNγR^CNSKO as compared to IFNγR^periKO mice. Contrary to what we anticipated, cerebella/brainstems of IFNγR^CNSKO mice were only minimally infiltrated, while the same areas of IFNγR^periKO mice were extensively populated by peripheral immune cells. Furthermore, the CNS of IFNγR^periKO mice was characterized by persistent neutrophil-rich foci as compared to IFNγR^CNSKO. Immunohistochemical analysis of the CNS of IFNγ-/- and IFNγR chimeric mice revealed that IFNγ protective actions are exerted through microglial STAT1.

Conclusions

Alterations in distribution and composition of CNS inflammatory foci are not sufficient for the onset of atypical EAE. IFNγ dictates the course of neuroinflammatory disorders mainly through actions exerted within the CNS. This study provides strong evidence that link microglial STAT1 inactivation to vestibular dysfunction.