Recent Advances in Diagnostic, Prognostic, and Disease-Monitoring Biomarkers in Multiple Sclerosis

Multiple sclerosis (MS) is a highly heterogeneous disease. Currently, a combination of clinical features, MRI, and cerebrospinal fluid markers are used in clinical practice for diagnosis and treatment decisions. In recent years, there has been considerable effort to develop novel biomarkers that better reflect the pathologic substrates of the disease to aid in diagnosis and early prognosis, evaluation of ongoing inflammatory activity, detection and monitoring of disease progression, prediction of treatment response, and monitoring of disease-modifying treatment safety. In this review, the authors provide an overview of promising recent developments in diagnostic, prognostic, and disease-monitoring/treatment-response biomarkers in MS.

Paradigm shifts in multiple sclerosis management: Implications for daily clinical practice

Multiple sclerosis (MS) is the most common chronic inflammatory neurological disease. The emergence of disease-modifying therapies (DMTs) has greatly improved disease activity control and progression of disability in MS patients. DMTs differ in their mode of action, route of administration, efficacy, and safety profiles, offering multiple options for clinicians. Personalized medicine aims at tailoring the therapeutic strategy to patients' characteristics and disease activity but also patients' needs and preferences. New therapeutic options have already changed treatment paradigms for patients with active relapsing MS (RMS). The traditional approach consists in initiating treatment with moderate-efficacy DMTs and subsequently, escalating to higher-efficacy DMTs when there is evidence of clinical and/or radiological breakthrough activity. Recent real-world studies suggest that initiation of high-efficacy DMTs from disease onset can improve long-term outcomes for RMS patients. In this article, we review different treatment strategies and discuss challenges associated with personalized therapy.

Contribution of Intravital Neuroimaging to Study Animal Models of Multiple Sclerosis

Multiple sclerosis (MS) is a complex and long-lasting neurodegenerative disease of the central nervous system (CNS), characterized by the loss of myelin within the white matter and cortical fibers, axonopathy, and inflammatory responses leading to consequent sensory-motor and cognitive deficits of patients. While complete resolution of the disease is not yet a reality, partial tissue repair has been observed in patients which offers hope for therapeutic strategies. To address the molecular and cellular events of the pathomechanisms, a variety of animal models have been developed to investigate distinct aspects of MS disease. Recent advances of multiscale intravital imaging facilitated the direct in vivo analysis of MS in the animal models with perspective of clinical transfer to patients. This review gives an overview of MS animal models, focusing on the current imaging modalities at the microscopic and macroscopic levels and emphasizing the importance of multimodal approaches to improve our understanding of the disease and minimize the use of animals.

Multiple sclerosis progression: time for a new mechanism-driven framework

Traditionally, multiple sclerosis has been categorised by distinct clinical descriptors-relapsing-remitting, secondary progressive, and primary progressive-for patient care, research, and regulatory approval of medications. Accumulating evidence suggests that the clinical course of multiple sclerosis is better considered as a continuum, with contributions from concurrent pathophysiological processes that vary across individuals and over time. The apparent evolution to a progressive course reflects a partial shift from predominantly localised acute injury to widespread inflammation and neurodegeneration, coupled with failure of compensatory mechanisms, such as neuroplasticity and remyelination. Ageing increases neural susceptibility to injury and decreases resilience. These observations encourage a new consideration of the course of multiple sclerosis as a spectrum defined by the relative contributions of overlapping pathological and reparative or compensatory processes. New understanding of key mechanisms underlying progression and measures to quantify progressive pathology will potentially have important and beneficial implications for clinical care, treatment targets, and regulatory decision-making.

Innate Immune Cell–Related Pathology in the Thalamus Signals a Risk for Disability Progression in Multiple Sclerosis

Background and Objectives

Our aim was to investigate whether 18-kDa translocator protein (TSPO) radioligand binding in gray matter (GM) predicts later disability progression in multiple sclerosis (MS).

Methods

In this prospective imaging study, innate immune cells were investigated in the MS patient brain using PET imaging. The distribution volume ratio (DVR) of the TSPO-binding radioligand [¹¹C]PK11195 was determined in 5 GM regions: thalamus, caudate, putamen, pallidum, and cortical GM. Volumetric brain MRI parameters were obtained for comparison. The Expanded Disability Status Scale (EDSS) score was assessed at baseline and after follow-up of 3.0 ± 0.3 (mean ± SD) years. Disability progression was defined as an EDSS score increase of 1.0 point or 0.5 point if the baseline EDSS score was ≥6.0. A forward-type stepwise logistic regression model was constructed to compare multiple imaging and clinical variables in their ability to predict later disability progression.

Results

The cohort consisted of 66 patients with MS and 18 healthy controls. Patients with later disability progression (n = 17) had more advanced atrophy in the thalamus, caudate, and putamen at baseline compared with patients with no subsequent worsening. TSPO binding was significantly higher in the thalamus among the patients with later worsening. The thalamic DVR was the only measured imaging variable that remained a significant predictor of disability progression in the regression model. The final model predicted disability progression with 52.9% sensitivity and 93.9% specificity with an area under the curve value of 0.82 (receiver operating characteristic curve).

Discussion

Increased TSPO radioligand binding in the thalamus has potential in predicting short-term disability progression in MS and seems to be more sensitive for this than GM atrophy measures.

Neuroinflammation in Parkinson's disease: a meta-analysis of PET imaging studies

Increasingly, evidence implicates an important role of neuroinflammation in neurodegeneration progression. Yet, brain imaging has not reached a consistent conclusion that neuroinflammation is involved in the pathogenesis of Parkinson's disease (PD). We aimed to review the evidence to quantitatively assess the existence and spatial distribution of neuroinflammation in the brain of PD patients. We systematically searched literature databases for case-control studies which used positron emission tomography to detect neuroinflammation represented by translocator protein (TSPO) levels in PD patients compared with healthy controls (HC). Standardized mean differences (SMD) were selected as effect sizes and random-effects models were used to combine effect sizes. Subgroup analyses for separate brain regions were conducted. Fifteen studies comprising 455 (HC = 198, PD = 238) participants and 19 brain regions were included. Compared to HC, PD patients had elevated TSPO levels in midbrain, putamen, anterior cingulate, posterior cingulate, thalamus, striatum, frontal, temporal, parietal, occipital, cortex, hippocampus, substantia nigra, pons, cerebellum, and caudate when using 1st-generation ligands. TSPO levels were elevated in the midbrain of PD patients when 2nd-generation ligands were used. We discussed the possible explanations of contrasting difference between these outcomes.

Hydroxychloroquine for Primary Progressive Multiple Sclerosis

OBJECTIVE

Primary progressive multiple sclerosis (PPMS) does not respond well to immunomodulatory or immunosuppressive treatment. Chronic activation of microglia has been implicated in the pathophysiology of PPMS. The antimalarial drug hydroxychloroquine (HCQ) reduces the activity of human microglia and has neuroprotective effects in vitro.

METHODS

We conducted a single-arm, phase II futility trial of 200 mg oral HCQ twice daily for 18 months. In an effort to investigate disability worsening in the absence of overt focal inflammation, we excluded participants with contrast enhancing lesions on a screening magnetic resonance imaging (MRI). The primary end point was ≥20% worsening on the timed 25-foot walk measured between 6 and 18 months of follow-up.

RESULTS

Based on original trial data, 40% of the cohort were expected to worsen. We used a Simon 2-stage design to compare a null hypothesis of 40% of the cohort worsening against the one-sided alternative of 20%. Using a 5% type 1 error rate and 80% power, HCQ treatment would be deemed successful if fewer than 10 of 35 participants experienced clinically significant worsening. The study met its primary end point, as only 8 of 35 participants worsened between 6 and 18 months. HCQ was overall well-tolerated, with adverse events in 82% and serious adverse events in 12% of participants. All serious adverse events were unlikely related to HCQ use.

INTERPRETATION

HCQ treatment was associated with reduced disability worsening in people with PPMS. HCQ is a promising treatment candidate in PPMS and should be investigated further in randomized controlled clinical trials. ANN NEUROL 2021;90:940-948.

Organic solvent-based tissue clearing techniques and their applications

Revealing the true structure of tissues and organs with tissue slicing technology is difficult since images reconstructed in three dimensions are easily distorted. To address the limitations in tissue slicing technology, tissue clearing has been invented and has recently achieved significant progress in three-dimensional imaging. Currently, this technology can mainly be divided into two types: aqueous clearing methods and solvent-based clearing methods. As one of the important parts of this technology, organic solvent-based tissue clearing techniques have been widely applied because of their efficient clearing speed and high clearing intensity. This review introduces the primary organic solvent-based tissue clearing techniques and their applications.

Diagnosis of Progressive Multiple Sclerosis From the Imaging Perspective: A Review

Importance

Although magnetic resonance imaging (MRI) is useful for monitoring disease dissemination in space and over time and excluding multiple sclerosis (MS) mimics, there has been less application of MRI to progressive MS, including diagnosing primary progressive (PP) MS and identifying patients with relapsing-remitting (RR) MS who are at risk of developing secondary progressive (SP) MS. This review addresses clinical application of MRI for both diagnosis and prognosis of progressive MS.

Observations

Although nonspecific, some spinal cord imaging features (diffuse abnormalities and lesions involving gray matter [GM] and ≥2 white matter columns) are typical of PPMS. In patients with PPMS and those with relapse-onset MS, location of lesions in critical central nervous system regions (spinal cord, infratentorial regions, and GM) and MRI-detected high inflammatory activity in the first years after diagnosis are risk factors for long-term disability and future progressive disease course. These measures are evaluable in clinical practice. In patients with established MS, GM involvement and neurodegeneration are associated with accelerated clinical worsening. Subpial demyelination and slowly expanding lesions are novel indicators of progressive MS.

Conclusions and Relevance

Diagnosis of PPMS is more challenging than diagnosis of RRMS. No qualitative clinical, immunological, histopathological, or neuroimaging features differentiate PPMS and SPMS; both are characterized by imaging findings reflecting neurodegeneration and are also impacted by aging and comorbidities. Unmet diagnostic needs include identification of MRI markers capable of distinguishing PPMS from RRMS and predicting the evolution of RRMS to SPMS. Integration of multiple parameters will likely be essential to achieve these aims.

Brain TSPO-PET predicts later disease progression independent of relapses in multiple sclerosis

Overactivation of microglia is associated with most neurodegenerative diseases. In this study we examined whether PET-measurable innate immune cell activation predicts multiple sclerosis disease progression. Activation of microglia/macrophages was measured using the 18-kDa translocator protein (TSPO)-binding radioligand ¹¹C-PK11195 and PET imaging in 69 patients with multiple sclerosis and 18 age- and sex-matched healthy controls. Radioligand binding was evaluated as the distribution volume ratio from dynamic PET images. Conventional MRI and disability measurements using the Expanded Disability Status Scale were performed for patients at baseline and 4.1 ± 1.9 (mean ± standard deviation) years later. Fifty-one (74%) of the patients were free of relapses during the follow-up period. Patients had increased activation of innate immune cells in the normal-appearing white matter and in the thalamus compared to the healthy control group (P = 0.033 and P = 0.003, respectively, Wilcoxon). Forward-type stepwise logistic regression was used to assess the best variables predicting disease progression. Baseline innate immune cell activation in the normal-appearing white matter was a significant predictor of later progression when the entire multiple sclerosis cohort was assessed [odds ratio (OR) = 4.26; P = 0.048]. In the patient subgroup free of relapses there was an association between macrophage/microglia activation in the perilesional normal-appearing white matter and disease progression (OR = 4.57; P = 0.013). None of the conventional MRI parameters measured at baseline associated with later progression. Our results strongly suggest that innate immune cell activation contributes to the diffuse neural damage leading to multiple sclerosis disease progression independent of relapses.

Imaging Butyrylcholinesterase in Multiple Sclerosis

PURPOSE

Molecular imaging agents targeting butyrylcholinesterase (BChE) have shown promise in other neurodegenerative disorders and may have utility in detecting changes to normal appearing white matter in multiple sclerosis (MS). BChE activity is present in white matter and localizes to activated microglia associated with MS lesions. The purpose of this study was to further characterize changes in the cholinergic system in MS pathology, and to explore the utility of BChE radioligands as potential diagnostic and treatment monitoring agents in MS.

PROCEDURE

Cortical and white matter lesions were identified using myelin staining, and lesions were classified based on microglial activation patterns. Adjacent brain sections were used for cholinesterase histochemistry and in vitro autoradiography using phenyl 4-[¹²³I]-iodophenylcarbamate (¹²³I-PIP), a previously described small-molecule cholinesterase-binding radioligand.

RESULTS

BChE activity is positively correlated with microglial activation in white matter MS lesions. There is no alteration in cholinesterase activity in cortical MS lesions. ¹²³I-PIP autoradiography revealed uptake of radioactivity in normal white matter, absence of radioactivity within demyelinated MS lesions, and variable uptake of radioactivity in adjacent normal-appearing white matter.

CONCLUSIONS

BChE imaging agents have the potential to detect MS lesions and subtle pathology in normal-appearing white matter in postmortem MS brain tissue. The possibility of BChE imaging agents serving to supplement current diagnostic and treatment monitoring strategies should be evaluated.

Changes of central noradrenaline transporter availability in immunotherapy-naïve multiple sclerosis patients

The neurotransmitter noradrenaline (NA) mediates arousal, attention and mood, and exerts anti-inflammatory and neuroprotective effects. Alterations of monoamine signalling were reported in multiple sclerosis (MS) and psychiatric illness and may account for the high prevalence of comorbid depression and fatigue in MS patients. We assessed central noradrenaline transporter (NAT) availability using positron emission tomography (PET) and the NAT selective radiotracer S,S-[¹¹C]O-methylreboxetine in immunotherapy-naïve patients with relapsing–remitting MS (RRMS; n = 11) compared to healthy controls (HC; n = 12), and its association to lesion load, time since manifestation, the expanded disability status scale (EDSS), the fatigue scale Würzburger Erschöpfungsinventar bei MS (WEIMuS) and Beck Depression Inventory (BDI). We found NAT availability to be increased in the thalamus, amygdala, putamen and pons/midbrain of MS patients. No relation to clinical or psychometric variables was found. These first data indicate higher NAT availability in subcortical brain regions of immunotherapy-naïve RRMS patients. If these changes of noradrenergic neurotransmission predispose to psychiatric symptoms or associate with disease activity needs to be investigated in longitudinal studies or a larger sample which allows subgroup analyses.

Identifying Progression in Multiple Sclerosis: New Perspectives

The identification of progression in multiple sclerosis is typically retrospective. Given the profound burden of progressive multiple sclerosis, and the recent development of effective treatments for these patients, there is a need to establish measures capable of identifying progressive multiple sclerosis early in the disease course. Starting from recent pathological findings, this review assesses the state of the art of potential measures able to predict progressive multiple sclerosis. Future promising biomarkers that might shed light on mechanisms of progression are also discussed. Finally, expansion of the concept of progressive multiple sclerosis, by including an assessment of cognition, patient-reported outcomes, and comorbidities, is considered. ANN NEUROL 2020;88:438-452.

MRI biomarkers of disease progression and conversion to secondary-progressive multiple sclerosis

INTRODUCTION

Conventional imaging measures remain a key clinical tool for the diagnosis multiple sclerosis (MS) and monitoring of patients. However, most measures used in the clinic show unsatisfactory performance in predicting disease progression and conversion to secondary progressive MS.

AREAS COVERED

Sophisticated imaging techniques have facilitated the identification of imaging biomarkers associated with disease progression, such as global and regional brain volume measures, and with conversion to secondary progressive MS, such as leptomeningeal contrast enhancement and chronic inflammation. The relevance of emerging imaging approaches partially overcoming intrinsic limitations of traditional techniques is also discussed.

EXPERT OPINION

Imaging biomarkers capable of detecting tissue damage early on in the disease, with the potential to be applied in multicenter trials and at an individual level in clinical settings, are strongly needed. Several measures have been proposed, which exploit advanced imaging acquisitions and/or incorporate sophisticated post-processing, can quantify irreversible tissue damage. The progressively wider use of high-strength field MRI and the development of more advanced imaging techniques will help capture the missing pieces of the MS puzzle. The ability to more reliably identify those at risk for disability progression will allow for earlier intervention with the aim to favorably alter the disease course.

The P2X7 receptor tracer [11C]SMW139 as an in vivo marker of neuroinflammation in multiple sclerosis: a first-in man study

Purpose

The novel PET tracer [¹¹C]SMW139 binds with high affinity to the P2X₇ receptor, which is expressed on pro-inflammatory microglia. The purposes of this first in-man study were to characterise pharmacokinetics of [¹¹C]SMW139 in patients with active relapsing remitting multiple sclerosis (RRMS) and healthy controls (HC) and to evaluate its potential to identify in vivo neuroinflammation in RRMS.

Methods

Five RRMS patients and 5 age-matched HC underwent 90-min dynamic [¹¹C]SMW139 PET scans, with online continuous and manual arterial sampling to generate a metabolite-corrected arterial plasma input function. Tissue time activity curves were fitted to single- and two-tissue compartment models, and the model that provided the best fits was determined using the Akaike information criterion.

Results

The optimal model for describing [¹¹C]SMW139 kinetics in both RRMS and HC was a reversible two-tissue compartment model with blood volume parameter and with the dissociation rate k₄ fixed to the whole-brain value. Exploratory group level comparisons demonstrated an increased volume of distribution (V_T) and binding potential (BP_ND) in RRMS compared with HC in normal appearing brain regions. BP_ND in MS lesions was decreased compared with non-lesional white matter, and a further decrease was observed in gadolinium-enhancing lesions. In contrast, increased V_T was observed in enhancing lesions, possibly resulting from disruption of the blood-brain barrier in active MS lesions. In addition, there was a high correlation between parameters obtained from 60- to 90-min datasets, although analyses using 60-min data led to a slight underestimation in regional V_T and BP_ND values.

Conclusions

This first in-man study demonstrated that uptake of [¹¹C]SMW139 can be quantified with PET using BP_ND as a measure for specific binding in healthy controls and RRMS patients. Additional studies are warranted for further clinical evaluation of this novel neuroinflammation tracer.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04550-x) contains supplementary material, which is available to authorized users.

Vascular aspects of multiple sclerosis: emphasis on perfusion and cardiovascular comorbidities

INTRODUCTION

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. Over the last two decades, more favorable MS long-term outcomes have contributed toward increase in prevalence of the aged MS population. Emergence of age-associated pathology, such as cardiovascular diseases, may interact with the MS pathophysiology and further contribute to disease progression. Areas covered: This review summarizes the cardiovascular involvement in MS pathology, its disease activity, and progression. The cardiovascular health, the presence of various cardiovascular diseases, and their effect on MS cognitive performance are further explored. In similar fashion, the emerging evidence of a higher incidence of extracranial arterial pathology and its association with brain MS pathology are discussed. Finally, the authors outline the methodologies behind specific perfusion magnetic resonance imaging (MRI) and ultrasound Doppler techniques, which allow measurement of disease-specific and age-specific vascular changes in the aging population and MS patients. Expert opinion: Cardiovascular pathology significantly contributes to worse clinical and MRI-derived disease outcomes in MS. Global and regional cerebral hypoperfusion may be associated with poorer physical and cognitive performance. Prevention, improved detection, and treatment of the cardiovascular-based pathology may improve the overall long-term health of MS patients.

Interferon β-Mediated Protective Functions of Microglia in Central Nervous System Autoimmunity

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and axonal damage. It often affects young adults and can lead to neurological disability. Interferon β (IFNβ) preparations represent widely used treatment regimens for patients with relapsing-remitting MS (RRMS) with therapeutic efficacy in reducing disease progression and frequency of acute exacerbations. In mice, IFNβ therapy has been shown to ameliorate experimental autoimmune encephalomyelitis (EAE), an animal model of MS while genetic deletion of IFNβ or its receptor augments clinical severity of disease. However, the complex mechanism of action of IFNβ in CNS autoimmunity has not been fully elucidated. Here, we review our current understanding of the origin, phenotype, and function of microglia and CNS immigrating macrophages in the pathogenesis of MS and EAE. In addition, we highlight the emerging roles of microglia as IFNβ-producing cells and vice versa the impact of IFNβ on microglia in CNS autoimmunity. We finally discuss recent progress in unraveling the underlying molecular mechanisms of IFNβ-mediated effects in EAE.

Application of advanced MRI techniques to monitor pharmacologic and rehabilitative treatment in multiple sclerosis: current status and future perspectives

Introduction: Advances in magnetic resonance imaging (MRI) technology and analyses are improving our understanding of the pathophysiology of multiple sclerosis (MS). Due to their ability to grade the presence of irreversible tissue loss, microstructural tissue abnormalities, metabolic changes and functional plasticity, the application of these techniques is also expanding our knowledge on the efficacy and mechanisms of action of different pharmacological and rehabilitative treatments. Areas covered: This review discusses recent findings derived from the application of advanced MRI techniques to evaluate the structural and functional substrates underlying the effects of pharmacologic and rehabilitative treatments in patients with MS. Current applications as outcome in clinical trials and observational studies, their interpretation and possible pitfalls in their use are discussed. Finally, how these techniques could evolve in the future to improve monitoring of disease progression and treatment response is examined. Expert commentary: The number of treatments currently available for MS is increasing. The application of advanced MRI techniques is providing reliable and specific measures to better understand the targets of different treatments, including neuroprotection, tissue repair, and brain plasticity. This is a fundamental progress to move toward personalized medicine and individual treatment selection.