Gray and normal-appearing white matter in multiple sclerosis: an MRI perspective

Routine MR Imaging Protocol and Standardization in Central Nervous System Demyelinating Diseases

Standardized MR imaging protocols are important for the diagnosis and monitoring of patients with multiple sclerosis (MS) and the appropriate use of MR imaging in routine clinical practice. Advances in using MR imaging to establish an earlier diagnosis of MS, safety concerns regarding intravenous gadolinium-based contrast agents, and the value of spinal cord MR imaging for diagnostic, prognostic, and monitoring purposes suggest a changing role of MR imaging for the management and care of MS patients. The MR imaging protocol emphasizes 3 dimensional acquisitions for optimal comparison over time.

Benefits of a mosaic approach for assessing cortical atrophy in individual multiple sclerosis patients

OBJECTIVE

Cortical gray matter (GM) atrophy plays a central role in multiple sclerosis (MS) pathology. However, it is not commonly assessed in clinical routine partly because a number of methodological problems hamper the development of a robust biomarker to quantify GM atrophy. In previous work, we have demonstrated the clinical utility of the "mosaic approach" (MAP) to assess individual GM atrophy in the motor neuron disease spectrum and frontotemporal dementia. In this study, we investigated the clinical utility of MAP in MS, comparing this novel biomarker to existing methods for computing GM atrophy in single patients. We contrasted the strategies based on correlations with established biomarkers reflecting MS disease burden.

METHODS

We analyzed T1-weighted MPRAGE magnetic resonance imaging data from 465 relapsing-remitting MS patients and 89 healthy controls. We inspected how variations of existing strategies to estimate individual GM atrophy ("standard approaches") as well as variations of MAP (i.e., different parcellation schemes) impact downstream analysis results, both on a group and an individual level. We interpreted individual cortical disease burden as single metric reflecting the fraction of significantly atrophic data points with respect to the control group. In addition, we evaluated the correlations to lesion volume (LV) and Expanded Disability Status Scale (EDSS).

RESULTS

We found that the MAP method yielded highest correlations with both LV and EDSS as compared to all other strategies. Although the parcellation resolution played a minor role in terms of absolute correlations with clinical variables, higher resolutions provided more clearly defined statistical brain maps which may facilitate clinical interpretability.

CONCLUSION

This study provides evidence that MAP yields high potential for a clinically relevant biomarker in MS, outperforming existing methods to compute cortical disease burden in single patients. Of note, MAP outputs brain maps illustrating individual cortical disease burden which can be directly interpreted in daily clinical routine.

Alterations in Sensorimotor and Mesiotemporal Cortices and Diffuse White Matter Changes in Primary Progressive Multiple Sclerosis Detected by Adiabatic Relaxometry

Background: The research of primary progressive multiple sclerosis (PPMS) has not been able to capitalize on recent progresses in advanced magnetic resonance imaging (MRI) protocols.

Objective: The presented cross-sectional study evaluated the utility of four different MRI relaxation metrics and diffusion-weighted imaging in PPMS.

Methods: Conventional free precession T1 and T2, and rotating frame adiabatic T1ρ and T2ρ in combination with diffusion-weighted parameters were acquired in 13 PPMS patients and 13 age- and sex-matched controls.

Results: T1ρ, a marker of crucial relevance for PPMS due to its sensitivity to neuronal loss, revealed large-scale changes in mesiotemporal structures, the sensorimotor cortex, and the cingulate, in combination with diffuse alterations in the white matter and cerebellum. T2ρ, particularly sensitive to local tissue background gradients and thus an indicator of iron accumulation, concurred with similar topography of damage, but of lower extent. Moreover, these adiabatic protocols outperformed both conventional T1 and T2 maps and diffusion tensor/kurtosis approaches, methods previously used in the MRI research of PPMS.

Conclusion: This study introduces adiabatic T1ρ and T2ρ as elegant markers confirming large-scale cortical gray matter, cerebellar, and white matter alterations in PPMS invisible to other in vivo biomarkers.

The features of cerebral permeability and perfusion detected by dynamic contrast-enhanced magnetic resonance imaging with Patlak model in relapsing-remitting multiple sclerosis

Objective

To investigate the features of cerebral permeability and perfusion detected by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with Patlak model in relapsing–remitting multiple sclerosis (RRMS) and their correlations with Expanded Disability Status Scale (EDSS) scores and disease duration.

Patients and methods

Twenty-seven RRMS patients underwent conventional MRI and DCE-MRI with 3.0 T magnetic resonance scanner were enrolled in the study. A Patlak model was used to quantitatively measure MRI biomarkers, including volume transfer constant (K^trans), fractional plasma volume (V_p), cerebral blood flow (CBF), and cerebral blood volume (CBV). The correlations of MRI biomarkers with EDSS scores and disease duration were analyzed.

Results

The MRI biomarkers K^trans, V_p, CBF, and CBV of contrast-enhancing (CE) lesions were significantly higher (P<0.05) than those of non-enhancing (NE) lesions and normal-appearing white matter (NAWM) regions. The skewness and kurtosis of K^trans values in CE lesions were significantly higher (P<0.05) than that of NE lesions. No significant correlation was found among the biomarkers with EDSS scores and disease duration (P>0.05).

Conclusion

Our study demonstrated the abnormalities of permeability and perfusion characteristics in multiple sclerosis (MS) lesions and NAWM regions by DCE-MRI with Patlak model. The K^trans, V_p, CBF, and CBV of CE lesions were significantly higher than that of NE lesions, but these MRI biomarkers did not associate with the severity and duration of the disease. The skewness and kurtosis of K^trans value in CE lesions were significantly higher than that in NE lesions, indicating that these parameters of K^trans histogram can be used to distinguish the pathology of MS lesions.

Multiple sclerosis animal models: a clinical and histopathological perspective

There is a broad consensus that multiple sclerosis (MS) represents more than an inflammatory disease: it harbors several characteristic aspects of a classical neurodegenerative disorder, that is, damage to axons, synapses and nerve cell bodies. While we are equipped with appropriate therapeutic options to prevent immune-cell driven relapses, effective therapeutic options to prevent the progressing neurodegeneration are still missing. In this review article, we will discuss to what extent pathology of the progressive disease stage can be modeled in MS animal models. While acute and relapsing-remitting forms of experimental autoimmune encephalomyelitis (EAE), which are T cell dependent, are aptly suited to model relapsing-remitting phases of MS, other EAE models, especially the secondary progressive EAE stage in Biozzi ABH mice is better representing the secondary progressive phase of MS, which is refractory to many immune therapies. Besides EAE, the cuprizone model is rapidly gaining popularity to study the formation and progression of demyelinating CNS lesions without T cell involvement. Here, we discuss these two non-popular MS models. It is our aim to point out the pathological hallmarks of MS, and discuss which pathological aspects of the disease can be best studied in the various animal models available.

Primary progressive multiple sclerosis: part of the MS disease spectrum or separate disease entity?

Multiple sclerosis (MS), the most frequent demyelinating disease, is characterized by a variable disease course. The majority of patients starts with relapsing remitting (RR) disease; approximately 50-60% of these patients progress to secondary progressive (SP) disease. Only about 15% of the patients develop a progressive disease course from onset, termed primary progressive multiple sclerosis (PPMS); the underlying pathogenic mechanisms responsible for onset of the disease with either PPMS or relapsing remitting multiple sclerosis (RRMS) are unknown. Patients with PPMS do not show a female predominance and usually have a later onset of disease compared to patients with RRMS. Monozygous twins can be concordant or discordant for disease courses indicating that the disease course is not only genetically determined. Primary progressive multiple sclerosis and secondary progressive multiple sclerosis (SPMS) share many similarities in imaging and pathological findings. Differences observed among the different disease courses are more of a quantitative than qualitative nature suggesting that the different phenotypes are part of a disease spectrum modulated by individual genetic predisposition and environmental influences. In this review, we summarize the knowledge regarding the clinical, epidemiological, imaging, and pathological characteristics of PPMS and compare those characteristics with RRMS and SPMS.

Axonal damage in multiple sclerosis

Multiple sclerosis is a debilitating disease of the central nervous system that has been characteristically classified as an immune-mediated destruction of myelin, the protective coating on nerve fibers. Although the mechanisms responsible for the immune attack to central nervous system myelin have been the subject of intense investigation, more recent studies have focused on the neurodegenerative component, which is cause of clinical disability in young adults and appears to be only partially controlled by immunomodulatory therapies. Here, we review distinct, but not mutually exclusive, mechanisms of pathogenesis of axonal damage in multiple sclerosis patients that are either consequent to long-term demyelination or independent from it. We propose that the complexity of axonal degeneration and the heterogeneity of the underlying pathogenetic mechanisms should be taken into consideration for the design of targeted therapeutic intervention.

FLT-3 expression and function on microglia in multiple sclerosis

Inflammatory cell infiltration and resident microglial activation within the central nervous system (CNS) are pathological events in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). While MS therapies target the peripheral immune system, no treatment is currently known to also modulate microglia. FMS-like tyrosine-3 (FLT-3) is expressed on hematopoietic and dendritic cells. We reported that FLT-3 inhibition ameliorates early actively induced EAE by predominantly modulating dendritic cell function as compared to microglia. We demonstrate in this report that FLT-3 is expressed in perivascular cuffs, brain parenchyma and in non-lesioned gray and white matter within MS brain but not in these regions within control brain. Furthermore, we demonstrate that FLT-3 is expressed on two populations of cells within MS brain; one which expresses the dendritic cell marker CD209, and the other which does not, suggesting that FLT-3 within MS brain is expressed on infiltrating dendritic cells and a non-dendritic cell such as microglia. Additionally, we report that FLT-3 inhibition in murine microglia blocks, in a dose-dependent manner, IFN-γ-induced expression of MHC class II and CD86, and LPS-induced secretion of IL-6. These data suggest that FLT-3 is involved in microglial cells' capacity to respond to environmental cues to function as antigen presenting cells and mediate CNS inflammation. Furthermore these data suggest that FLT-3 may be a therapeutic target on microglia to mitigate CNS inflammation.

Infratentorial lesion volume correlates with sensory functional system in multiple sclerosis patients: a 3.0-Tesla MRI study

PURPOSE

This study sought to correlate lesion volume in infratentorial areas using 3.0-T proton-density (PD)-weighted images with disability scales and appropriate functional system scores in patients with multiple sclerosis (MS).

MATERIALS AND METHODS

We examined 20 consecutive patients (13 women and 7 men) with a median age of 47 years (range 26-70). Neurological examination included the Expanded Disability Status Scale and its functional systems, the Barthel Index (BI) and the Rivermead Mobility Index (RMI). MRI scans were performed on a system operating at 3.0 T using a quadrature birdcage head coil. Acquired images imported as Digital Imaging and Communication in Medicine (DICOM) files, and the region of interest (ROI) files were converted to Neuroimaging Informatics Technology Initiative (NIfTI) format and normalised to the Montreal Neurological Institute (MNI) standard template. An automated segmentation algorithm was used to distinguish between supratentorial and infratentorial areas. Normalisation to the magnetisation-prepared rapid acquisition with gradient echo (MPRAGE) T1-weighted sequence allowed lesion volume estimation in the different anatomical areas.

RESULTS

A significant correlation was found between infratentorial lesion volume and the sensory functional system score (rho=0.76, p=0.002). No significant correlation was found between supratentorial lesion volume and Expanded Disability Status Scale (EDSS), RMI and BI scores.

CONCLUSIONS

The described method, by means of anatomical assignment of MS lesions, allows detection of significant correlation coefficients between clinical and MRI lesion burden in MS patients at the infratentorial level.

Multiple sclerosis lesions: insights from imaging techniques

The hallmark of multiple sclerosis (MS) pathology is the presence of inflammatory demyelinated lesions distributed throughout the CNS. Along with more diffuse tissue abnormalities, it is considered one of the major determinants of neurological deficit in MS. Conventional MRI has contributed to improve our understanding of MS pathology and has provided objective and reliable measures to monitor the effect of treatments. Advanced MRI techniques have offered the opportunity to quantify pathological changes in lesions, as well as in normal-appearing brain tissue and to characterize their dynamics. This review will discuss the characteristics and development of MS lesions and the contribution of conventional and quantitative MRI techniques to understanding pathological changes associated with them.

Neuroaxonal ion dyshomeostasis of the normal-appearing corpus callosum in experimental autoimmune encephalomyelitis

Atrophy of the corpus callosum (CC) is a well-documented observation in clinically definite multiple sclerosis (MS) patients. One recent hypothesis for the neurodegeneration that occurs in MS is that ion dyshomeostasis leads to neuroaxonal damage. To examine whether ion dyshomeostasis occurs in the CC during MS onset, experimental autoimmune encephalomyelitis (EAE) was utilized as an animal MS model to induce autoimmunity-mediated responses. To date, in vivo investigations of neuronal ion homeostasis has not been feasible using traditional neuroscience techniques. Therefore, the current study employed an emerging MRI method, called Mn2+-enhanced MRI (MEMRI). Mn2+ dynamics is closely associated with important neuronal activity events, and is also considered to be a Ca2+ surrogate. Furthermore, when injected intracranially, Mn2+ can be used as a multisynaptic tracer. These features enable MEMRI to detect neuronal ion homeostasis within a multisynaptic circuit that is connected to the injection site. Mn2+ was injected into the visual cortex to trace the CC, and T1-weighted imaging was utilized to observe temporal changes in Mn2+-induced signals in the traced pathways. The results showed that neuroaxonal functional changes associated with ion dyshomeostasis occurred in the CC during an acute EAE attack. In addition, the pathway appeared normal, although EAE-induced immune-cell infiltration was visible around the CC. The findings suggest that ion dyshomeostasis is a major neuronal aberration underlying the deterioration of normal-appearing brain tissues in MS, supporting its involvement in neuroaxonal functioning in MS.