Relationship of grey and white matter abnormalities with distance from the surface of the brain in multiple sclerosis

OBJECTIVE: To assess the association between proximity to the inner (ventricular and aqueductal) and outer (pial) surfaces of the brain and the distribution of normal appearing white matter (NAWM) and grey matter (GM) abnormalities, and white matter (WM) lesions, in multiple sclerosis (MS). METHODS: 67 people with relapse-onset MS and 30 healthy controls were included in the study. Volumetric T1 images and high-resolution (1 mm(3)) magnetisation transfer ratio (MTR) images were acquired and segmented into 12 bands between the inner and outer surfaces of the brain. The first and last bands were discarded to limit partial volume effects with cerebrospinal fluid. MTR values were computed for all bands in supratentorial NAWM, cerebellar NAWM and brainstem NA tissue, and deep and cortical GM. Band WM lesion volumes were also measured. RESULTS: Proximity to the ventricular surfaces was associated with progressively lower MTR values in the MS group but not in controls in supratentorial and cerebellar NAWM, brainstem NA and in deep and cortical GM. The density of WM lesions was associated with proximity to the ventricles only in the supratentorial compartment, and no link was found with distance from the pial surfaces. CONCLUSIONS: In MS, MTR abnormalities in NAWM and GM are related to distance from the inner and outer surfaces of the brain, and this suggests that there is a common factor underlying their spatial distribution. A similar pattern was not found for WM lesions, raising the possibility that different factors promote their formation

Reduced neurite density in the brain and cervical spinal cord in relapsing–remitting multiple sclerosis: A NODDI study

Background: Multiple sclerosis (MS) affects both brain and spinal cord. However, studies of the neuraxis with advanced magnetic resonance imaging (MRI) are rare because of long acquisition times. We investigated neurodegeneration in MS brain and cervical spinal cord using neurite orientation dispersion and density imaging (NODDI). / Objective: The aim of this study was to investigate possible alterations, and their clinical relevance, in neurite morphology along the brain and cervical spinal cord of relapsing–remitting MS (RRMS) patients. / Methods: In total, 28 RRMS patients and 20 healthy controls (HCs) underwent brain and spinal cord NODDI at 3T. Physical and cognitive disability was assessed. Individual maps of orientation dispersion index (ODI) and neurite density index (NDI) in brain and spinal cord were obtained. We examined differences in NODDI measures between groups and the relationships between NODDI metrics and clinical scores using linear regression models adjusted for age, sex and brain tissue volumes or cord cross-sectional area (CSA). / Results: Patients showed lower NDI in the brain normal-appearing white matter (WM) and spinal cord WM than HCs. In patients, a lower NDI in the spinal cord WM was associated with higher disability. / Conclusion: Reduced neurite density occurs in the neuraxis but, especially when affecting the spinal cord, it may represent a mechanism of disability in MS

Single-subject structural cortical networks in clinically isolated syndrome

BACKGROUND: Structural cortical networks (SCNs) represent patterns of coordinated morphological modifications in cortical areas, and they present the advantage of being extracted from previously acquired clinical magnetic resonance imaging (MRI) scans. SCNs have shown pathophysiological changes in many brain disorders, including multiple sclerosis. OBJECTIVE: To investigate alterations of SCNs at the individual level in patients with clinically isolated syndrome (CIS), thereby assessing their clinical relevance. METHODS: We analyzed baseline data collected in a prospective multicenter (MAGNIMS) study. CIS patients (n = 60) and healthy controls (n = 38) underwent high-resolution 3T MRI. Measures of disability and cognitive processing were obtained for patients. Single-subject SCNs were extracted from brain 3D-T1 weighted sequences; global and local network parameters were computed. RESULTS: Compared to healthy controls, CIS patients showed altered small-world topology, an efficient network organization combining dense local clustering with relatively few long-distance connections. These disruptions were worse for patients with higher lesion load and worse cognitive processing speed. Alterations of centrality measures and clustering of connections were observed in specific cortical areas in CIS patients when compared with healthy controls. CONCLUSION: Our study indicates that SCNs can be used to demonstrate clinically relevant alterations of connectivity in CIS

Single-subject structural cortical networks in clinically isolated syndrome.

BACKGROUND: Structural cortical networks (SCNs) represent patterns of coordinated morphological modifications in cortical areas, and they present the advantage of being extracted from previously acquired clinical magnetic resonance imaging (MRI) scans. SCNs have shown pathophysiological changes in many brain disorders, including multiple sclerosis. OBJECTIVE: To investigate alterations of SCNs at the individual level in patients with clinically isolated syndrome (CIS), thereby assessing their clinical relevance. METHODS: We analyzed baseline data collected in a prospective multicenter (MAGNIMS) study. CIS patients (n = 60) and healthy controls (n = 38) underwent high-resolution 3T MRI. Measures of disability and cognitive processing were obtained for patients. Single-subject SCNs were extracted from brain 3D-T1 weighted sequences; global and local network parameters were computed. RESULTS: Compared to healthy controls, CIS patients showed altered small-world topology, an efficient network organization combining dense local clustering with relatively few long-distance connections. These disruptions were worse for patients with higher lesion load and worse cognitive processing speed. Alterations of centrality measures and clustering of connections were observed in specific cortical areas in CIS patients when compared with healthy controls. CONCLUSION: Our study indicates that SCNs can be used to demonstrate clinically relevant alterations of connectivity in CIS

Investigation of pathophysiological mechanisms in clinically isolated syndrome using advanced imaging techniques

This thesis concerns an observational study of patients recruited after their first episode of neurological symptoms suggestive of demyelination in the central nervous system and diagnosed either with clinically isolated syndrome or relapsing-remitting multiple sclerosis. In multiple sclerosis, brain tissues can exhibit extensive neuroaxonal microstructural and metabolic abnormalities, but little is known about their presence and significance at the time of the first demyelinating episode. I used a novel multi-parametric quantitative MRI approach, combining neurite orientation dispersion and density imaging (NODDI), which gives information about tissue microstructure, and 23Na MRI, which estimates total sodium concentration, a marker of metabolic dysfunction, in the brains of clinically isolated syndrome patients. I found microstructural and sodium homeostasis alterations in cortical areas of patients that showed clinical relevance. Within the diffuse axonal dispersion found in the normal-appearing white matter, the corpus callosum shared with lesions, signs of axonal damage and metabolic dysfunction, thus emerging as a possible target for early neuroprotective interventions. Structural cortical networks (SCNs) represent patterns of coordinated morphological modifications in cortical areas and they have shown pathophysiological changes in many brain disorders, including multiple sclerosis. I investigated alterations of SCNs at the individual level in this early cohort. Patients showed altered small-world topology, an efficient network organization combining dense local clustering with relatively few long-distance connections. These disruptions were worse for patients with higher lesion load and worse cognitive processing speed indicating that pathophysiological changes in the cortical morphology can influence clinical outcomes. Finally, I hypothesised that the patients in the cohort presenting with optic neuritis may have disturbances in neuropsychological functions related to visual processes. I found that cognitive visuospatial processing is affected after unilateral optic neuritis and improves over time with visual recovery, independently of the structural damage in the visual and central nervous system

Grey matter pathology in multiple sclerosis: in vivo and post mortem magnetic resonance imaging studies

The extent and clinical relevance of grey matter (GM) pathology in multiple sclerosis (MS) is increasingly recognised. Previous work has shown that GM pathology is more closely associated with some aspects of clinical disability than white matter (WM) injury, which has been suggested to arise independently. Magnetic resonance imaging (MRI) allows the study of GM lesions, atrophy, and non-lesional injury with techniques including double inversion recovery (DIR), volumetric scans, and magnetisation transfer ratio (MTR), respectively. This thesis includes three independent in vivo and post mortem MRI studies specifically addressing (1) the clinical impact and spatial distribution of DIR-detected GM lesions and atrophy, (2) the longitudinal development of MTR changes in thalamo-cortical systems, and (3) the histopathological substrates underlying MTR in the MS brain. This work shows that (1) DIR-detected GM lesions are mainly found throughout the cerebellar and cerebral cortex, whereas particularly subcortical GM structures show atrophy. Both GM lesions and atrophy contribute to disability, suggesting that the substrates of disability in MS are both pathologically and spatially heterogeneous. (2) WM injury to thalamo-cortical systems is most likely to precede (both thalamic and cortical) GM damage. In addition, lower regional cortical MTR is found not to be consistently associated with lower cortical volume, suggesting that significant cortical microstructural damage can occur in the absence of atrophy. Furthermore, observed hemispheric asymmetries and WM tract inhomogeneities emphasise the need for more refined statistical models to detect disease-specific changes. (3) MTR is associated with histologically quantified myelin (and to a lesser extent neuronal content) in normal appearing grey matter and normal appearing white matter, but not in cortical lesions and chronic inactive WM lesions. Finally, the cytological make-up differs significantly between normal appearing and lesional WM and GM, and provides extra evidence for microglia-mediated mitochondria damage in normal appearing MS tissue

Exploring Outcome Measures of disease progression in Secondary Progressive Multiple Sclerosis

Multiple sclerosis (MS) is a disabling and progressive neurological disease affecting more than 120,000 people in the UK and 2.5 million people worldwide. Most people diagnosed with relapsing-remitting MS (RRMS) experience a late phase of the disease characterised by gradual progression of impairment of neurological function, known as secondary progressive MS (SPMS). The underlying cause of disability accrual in SPMS is attributed to progressive neuro-axonal loss (neurodegeneration). Unlike RRMS, treatments for SPMS are lacking and research from clinical trials has provided only modest positive results. This thesis concerns my work on a multi-centre, multi-arm, placebo-controlled phase 2B clinical trial (MS-SMART, ClinicalTrials.gov NCT01910259) investigating neuroprotection in SPMS. Through this trial, I investigated: (1) cross-sectional relationships between clinical and radiological outcomes that characterise a well-defined UK SPMS population not on disease-modifying therapy; (2) whether amiloride, fluoxetine and riluzole – the three pre-identified putative neuroprotective drugs used in the MS-SMART trial – reduced the rate of MRI-derived brain atrophy compared to placebo; (3) whether spinal cord MRI measures - reflecting cord damage and atrophy - were predictors of long-term disease course in people with SPMS and could be reliably used as outcome measures in future phase 2 trials; and (4) whether optical coherence tomography (OCT) measures were predictors of long-term disease course in people with SPMS and had a role in the measurement of neuroaxonal loss in future phase 2 trials. I collected several measures of disability, which included the expanded disability status scale (EDSS), the symbol digit modalities test (SDMT), the multiple sclerosis functional composite (MSFC) and its sub-components (9-holep peg test, timed 25-foot walk, paced auditory serial addition test), and multiple sclerosis impact scale (MSIS-29v2). To characterise the trial cohort at baseline and identify the variables that could better explain the sample variance, I used some sophisticated statistical analyses (principal component analysis, LASSO regression analysis) which helped to deal with the multiplicity of the variables. I also looked at some of the MS symptoms onset and comorbidities and their relationships with disease severity using multivariate analyses. To investigate neuroprotection in the whole trial cohort, I measured MRI-derived percentage brain volume change, which is thought to reflect neuroaxonal integrity and disability. The percentage brain volume change was analysed with the SIENA method. As MS-related disability is also referable to spinal cord damage, which is seen in up to 90% of patients with MS, I investigated spinal cord MRI abnormalities in the UCL cohort. I measured the cervical cord lesion number and volume, and calculated cord cross-sectional area using the active surface model. Additionally, I measured the cross-sectional area using two different pipelines to improve reduceing variability and get more reliable results. Although MRI techniques are reliable and sensitive surrogate biomarkers of axonal pathology in MS, they are expensive, time consuming and not easily accessible. OCT is an emerging imaging technique that enables the measurement of the neural retina, whose layer thinning reflect axonal loss. In order to do so, I used a Heidelberg Spectralis OCT machine and measured the peripapillary retinal nerve fibre layer and the ganglion cell plus the inner plexiform layer thicknesses. Both participants from UCL and Edinburgh trial sites were included. From December 2014 to June 2016, I actively recruited 176 subjects at UCL. In total, 445 subjects were enrolled in the MS-SMART trial across the UK. The baseline analysis of the whole cohort showed that none of the clinical measures could explain the sample variance in isolation and that the SDMT – a measure of processing speed – emerged as the strongest explanatory component, although it could not explain more than 30% of the sample variance. The SDMT and the body mass index were the strongest predictor of whole brain volume. I also found that a history of optic neuritis at MS onset did not predict a better SPMS prognosis, while a history of hypertension was related to higher disease severity. The primary trial analysis findings were negative, meaning that there was no difference in terms of percentage brain volume change between any of the three active arms and the placebo. This suggested that amiloride, fluoxetine and riluzole had no neuroprotective effects. The annualised percentage brain volume change was -0.87%. In the fluoxetine arm, there was a significant pseudoatrophy at 24 weeks suggesting perhaps possible neuromodulation with some anti-inflammatory effects. Spinal cord atrophy occurred at a rate of -0.66% per year on average. Both spinal cord area and brain volume measures at baseline were significantly associated with EDSS at baseline and at 96 weeks. However, only spinal cord area at baseline, and not brain volume, seemed to predict confirmed disability progression at 96 weeks (OR= 0.94; 95% CI= 0.89 to 0.98, p= 0.01). The results from the two different spinal cord MRI analysis pipelines showed that head position into the scanner and lack of registration between baseline and follow-up would lead to substantial variability. However, when the sample size was larger, the two pipelines seemed to offer similar results. OCT measures showed significant mean annual thinning independent of age. Additionally, baseline OCT measures could significantly predict clinical changes as measured by the two most common clinical metrics (EDSS and MSFC) and with the MRI-derived percentage brain volume change at 96 weeks. There was no correlation between annualised atrophy rates of OCT measures and MRI percentage brain volume change or EDSS change. In summary, the cross-sectional analysis of the baseline characteristics of the trial cohort showed that the SDMT is an important clinical variable which correlates significantly with other clinical and MRI parameters. My study suggests that SDMT should be collected in all cross-sectional studies in SPMS. I found that multi-arm trials are feasible in a UK population of people with SPMS. None of the three drugs – amiloride, fluoxetine, and riluzole - had neuroprotective effects, suggesting that future trials in SPMS should focus on different agents with different mechanisms of action. The role of fluoxetine as an anti-inflammatory was questionable and might deserve more investigations in the future. I also found that the annual rates of brain volume and spinal cord atrophy were similar, although brain volume atrophy was slightly higher than spinal cord atrophy. However, both these measures were significantly associated with EDSS. Brain volume had the advantage of being associated with the timed 25-foot walk measure; whereas, spinal cord area had the advantage to predict confirmed disability progression at 96 weeks. OCT measures significantly decreased over time independently of patients’ age. Baseline OCT measures could predict EDSS changes and EDSS at 96 weeks, but the percentage change of OCT measures had no relation with EDSS changes, suggesting that the observation time of 96 weeks was insufficient to detect clinically meaningful OCT changes. In conclusion, analysing a large cohort of patients with SPMS enrolled in a phase 2B trial provided a large data set which served to explore outcome measures of disease progression. I found that none of the clinical, MRI or OCT variables was optimal, in isolation, to measure SPMS disability or progression. OCT and spinal cord MRI did not seem to provide better outcomes compared to MRI brain measures alone, implying that they could measure different aspects of the pathology underlying SPMS. My work suggests that investigation of composite outcome measures of multimodal variables might be the way forward to find more sensitive outcome measures for quantifying disability changes. Finally, my work also shows that multi-arm trials investigating different agents at the same time are feasible and advantageous in SPMS and should be replicated in MS and extended to other chronic neurological disorders

Neuromyelitis optica (NMO): identifying imaging markers to improve diagnosis and inform therapeutic innovation

The main objective of the thesis is to use advanced MRI techniques to look for biomarkers that separate neuromyelitis optica spectrum disorders (NMOSD) from MS to improve diagnosis. NMOSD, a severe inflammatory disease which causes demyelination of the central nervous system, is characterised by optic neuritis (ON) and acute myelitis. Because of similarities with MS, NMOSD is not always correctly diagnosed at onset. As it is both more aggressive and faster progressing than MS, an early accurate diagnosis is crucial. For this thesis, three different MRI techniques were used, together with clinical assessments, to gain a better understanding of the differences between the two diseases. The first was neurite orientation dispersion and density imaging (NODDI), a diffusion MR technique used to analyse the microstructure of dendrites and axons. When applied to a single-shell dataset of RRMS patients, it was shown to detect more regions of diffusion abnormalities than FA maps. The second technique used is phase-sensitive inversion recovery (PSIR), to look for grey matter lesions. This first application to NMOSD patients led to the detection of grey matter lesions in nearly 50% of this group, as well as showing differences in leucocortical and juxtacortical lesions between NMOSD and MS, with juxtacortical lesions emerging as potential markers to differentiate between these diseases. The final part applies magnetisation transfer ratio (MTR) to the optic nerve to assess myelin integrity in both MS and NMOSD patients, together with optic coherence tomography (OCT) for the macula the retinal nerve fibre layer and visual assessments. Significant differences in MTR and OCT values were found in MS and NMOSD patients with ON compared to healthy controls (HC). Significant differences were found between the unaffected nerve of NMOSD patients and HC, but not between groups for either MTR values (after correction for age) and OCT measurements