MRI measures of neuroprotection and repair in multiple sclerosis

Magnetic Resonance Imaging in Primary Progressive Multiple Sclerosis Patients : Review

The recently developed effective treatment of primary progressive multiple sclerosis (PPMS) requires the accurate diagnosis of patients with this type of disease. Currently, the diagnosis of PPMS is based on the 2017 McDonald criteria, although the contribution of magnetic resonance imaging (MRI) to this process is fundamental. PPMS, one of the clinical types of MS, represents 10%-15% of all MS patients. Compared to relapsing-remitting MS (RRMS), PPMS differs in terms of pathology, clinical presentation and MRI features. Regarding conventional MRI, focal lesions on T2-weighted images and acute inflammatory lesions with contrast enhancement are less common in PPMS than in RRMS. On the other hand, MRI features of chronic inflammation, such as slowly evolving/expanding lesions (SELs) and leptomeningeal enhancement (LME), and brain and spinal cord atrophy are more common MRI characteristics in PPMS than RRMS. Nonconventional MRI also shows differences in subtle white and grey matter damage between PPMS and other clinical types of disease. In this review, we present separate diagnostic criteria, conventional and nonconventional MRI specificity for PPMS, which may support and simplify the diagnosis of this type of MS in daily clinical practice.

Spinal cord volume loss: A marker of disease progression in multiple sclerosis

OBJECTIVE

Cross-sectional studies have shown that spinal cord volume (SCV) loss is related to disease severity in multiple sclerosis (MS). However, long-term data are lacking. Our aim was to evaluate SCV loss as a biomarker of disease progression in comparison to other MRI measurements in a large cohort of patients with relapse-onset MS with 6-year follow-up.

METHODS

The upper cervical SCV, the total brain volume, and the brain T2 lesion volume were measured annually in 231 patients with MS (180 relapsing-remitting [RRMS] and 51 secondary progressive [SPMS]) over 6 years on 3-dimensional, T1-weighted, magnetization-prepared rapid-acquisition gradient echo images. Expanded Disability Status Scale (EDSS) score and relapses were recorded at every follow-up.

RESULTS

Patients with SPMS had lower baseline SCV (p < 0.01) but no accelerated SCV loss compared to those with RRMS. Clinical relapses were found to predict SCV loss over time (p < 0.05) in RRMS. Furthermore, SCV loss, but not total brain volume and T2 lesion volume, was a strong predictor of EDSS score worsening over time (p < 0.05). The mean annual rate of SCV loss was the strongest MRI predictor for the mean annual EDSS score change of both RRMS and SPMS separately, while correlating stronger in SPMS. Every 1% increase of the annual SCV loss rate was associated with an extra 28% risk increase of disease progression in the following year in both groups.

CONCLUSION

SCV loss over time relates to the number of clinical relapses in RRMS, but overall does not differ between RRMS and SPMS. SCV proved to be a strong predictor of physical disability and disease progression, indicating that SCV may be a suitable marker for monitoring disease activity and severity.

Intensity ratio to improve black hole assessment in multiple sclerosis

BACKGROUND

Improved imaging methods are critical to assess neurodegeneration and remyelination in multiple sclerosis. Chronic hypointensities observed on T1-weighted brain MRI, "persistent black holes," reflect severe focal tissue damage. Present measures consist of determining persistent black holes numbers and volumes, but do not quantitate severity of individual lesions.

OBJECTIVE

Develop a method to differentiate black and gray holes and estimate the severity of individual multiple sclerosis lesions using standard magnetic resonance imaging.

METHODS

38 multiple sclerosis patients contributed images. Intensities of lesions on T1-weighted scans were assessed relative to cerebrospinal fluid intensity using commercial software. Magnetization transfer imaging, diffusion tensor imaging and clinical testing were performed to assess associations with T1w intensity-based measures.

RESULTS

Intensity-based assessments of T1w hypointensities were reproducible and achieved > 90% concordance with expert rater determinations of "black" and "gray" holes. Intensity ratio values correlated with magnetization transfer ratios (R = 0.473) and diffusion tensor imaging metrics (R values ranging from 0.283 to -0.531) that have been associated with demyelination and axon loss. Intensity ratio values incorporated into T1w hypointensity volumes correlated with clinical measures of cognition.

CONCLUSIONS

This method of determining the degree of hypointensity within multiple sclerosis lesions can add information to conventional imaging.

The use of multiparametric quantitative magnetic resonance imaging for evaluating visually assigned lesion groups in patients with multiple sclerosis

In multiple sclerosis (MS), inflammatory lesions present a broad spectrum of histopathologic processes. For a better discrimination, lesions are visually defined into different lesion groups according to their appearance on conventional magnetic resonance imaging (MRI). The aim of this study was to investigate the properties of different MS lesion groups using multiparametric quantitative MRI. 35 patients diagnosed with relapsing-remitting MS received 3 Tesla MRI including magnetization-prepared 2 rapid acquisition gradient echo, diffusion tensor imaging and magnetization transfer imaging. Lesion segmentation was performed for T2 lesions, black holes and contrast-enhancing lesions. A subtraction mask was created including only T2 lesions that did not correspond to a black hole or contrast-enhancing lesion. T1 relaxation time (T1-RT), magnetization transfer ratio (MTR), mean diffusivity (MD) and fractional anisotropy (FA) were determined for every lesion and in normal-appearing white matter. Only MD differed significantly between all lesion groups and NAWM (p < 0.05), while FA differed between all lesion groups but not NAWM. T1-RT and MTR were not useful imaging biomarkers to distinguish between lesion groups. A lack of sensitivity and specificity and unproportional alterations of quantitative MRI measures, due to heterogenous histopathologic processes within lesions, may be a possible explanation for missing discrimination. Thus, not only interpretation of visually defined MS lesion but also interpretation of quantitative MRI measures remains challenging and should be conducted carefully.

The association between retinal nerve fibre layer thickness and N-acetyl aspartate levels in multiple sclerosis brain normal-appearing white matter: a longitudinal study using magnetic resonance spectroscopy and optical coherence tomography

BACKGROUND AND PURPOSE

N-acetyl aspartate (NAA) assessed using proton magnetic resonance spectroscopy (¹ H MRS) has a high pathological specificity for axonal density. Retinal nerve fibre layer thickness (RNFLT) measured by using optical coherence tomography is increasingly used as a surrogate marker of neurodegeneration in multiple sclerosis (MS). Our aim was to investigate the relation between RNFLT and NAA/creatine in brain normal-appearing white matter (NAWM), their dynamics over time and the association with clinical outcome measures in relapsing MS. T2 WM lesions served as control tissue.

METHODS

Forty-three MS patients underwent standardized neurological examination including the Expanded Disability Status Scale (EDSS), Multiple Sclerosis Functional Composite (MSFC) score, optical coherence tomography and magnetic resonance imaging including ¹ H MRS at baseline and after 1 year.

RESULTS

At baseline, NAA/creatine level was lower in T2 WM lesions than in NAWM (1.64 ± 0.16 vs. 1.88 ± 0.24, P < 0.001). Lowest levels were found in secondary progressive MS (SPMS). Mean RNFLT was higher in clinically isolated syndrome than in the combined group of relapsing-remitting MS and SPMS (99.8 ± 12.3 μm vs. 92.4 ± 12.8 μm, P = 0.038). In all patients, mean RNFLT decreased by 1.4% during follow-up. At baseline, MSFC z-scores correlated with NAA/creatine levels both in NAWM (r = 0.42; P = 0.008) and T2 WM lesions (r = 0.52, P = 0.004). NAWM NAA/creatine variation correlated with the RNFLT change over 1 year (ρ = 0.43, P = 0.046).

CONCLUSIONS

N-acetyl aspartate/creatine level reduction correlated with RNFLT thinning over 1 year in an EDSS stable MS cohort suggesting that these techniques might be sensitive to detect subclinical disease progression.

Review of methodological issues of clinical trials in multiple sclerosis

There are currently six approved disease-modifying therapies available to the physician for the treatment of multiple sclerosis. Their efficacy on clinical and radiological parameters has been demonstrated in Phase III pivotal clinical trials over the past two decades. Perceptions of the relative potency of these treatments have been driven principally by the response measured relative to a placebo group. However, efficacy comparisons between trials is of limited value because of differences in study methodology, in characteristics of the patient populations included, in the behaviour of the placebo group during the trial and in the time at which the trial was conducted. Moreover, and most importantly, the assumption that the efficacy observed in clinical trial settings is the same as that achievable in everyday clinical practice is inevitably flawed. Impressions of the relative efficacy of two treatments may differ dramatically depending on whether absolute or relative differences with respect to placebo are compared. Randomised direct comparative trials are therefore the only objective way to evaluate the relative efficacy of two therapies. It is clear that between-treatment differences are difficult to quantify in short-term studies and require large numbers of patients. Long-term outcome is increasingly important to monitor in spite of the inherent methodological limitations in order to establish the safety profile of a potentially lifelong treatment. New disease-modifying treatments for multiple sclerosis will soon be available. Although these are eagerly awaited, their risk-benefit profile, and their place in therapy, will only be adequately understood once real-life and long-term use has been documented as well as it has been for current treatments. Over the last two decades, considerable advances have been made in the methodology of clinical trials in multiple sclerosis. Consensual standardised protocols have been designed and validated for Phase II and Phase III trials, with standardised definitions for short-term clinical and radiological outcome measures. The elaboration and implementation of this methodology were possible through international collaborations, and this has enabled extensive experience to be gained throughout the world. These trials have laid the foundation for an evidence-based medicine approach to the treatment of multiple sclerosis. Clinical trials in multiple sclerosis have to some extent become a victim of their own success, with more and more trials competing for a limited pool of patients and limited resources. Modern trials require large number of patients to generate adequate statistical power and this in turn entails recruitment in many countries across different continents. This increases the complexity and cost of the study, and contract research organisations now play a dominant role in the logistics and administration of these trials. The challenge in conducting trials on a global basis involving large numbers of countries is to ensure that this heterogeneity does not impinge on the reliability of the findings. This may happen due to differences in the patient populations included in different countries, access to or experience with methods in evaluation, for example certain magnetic resonance imaging (MRI) protocols, and also due to ethical considerations. In addition, whether disease-modifying treatments are reimbursed in a given country or not will influence what sort of patients are likely to get included in clinical trial protocols.