Contrast-enhanced MR imaging in the evaluation of treatment response and prediction of outcome in multiple sclerosis

Monitoring Blood-Brain Barrier Integrity Following Amyloid-β Immunotherapy Using Gadolinium-Enhanced MRI in a PDAPP Mouse Model

BACKGROUND

Amyloid-related imaging abnormalities (ARIA) have been reported with some anti-amyloid-β (Aβ) immunotherapy trials. They are detected with magnetic resonance imaging (MRI) and thought to represent transient accumulation of fluid/edema (ARIA-E) or microhemorrhages (ARIA-H). Although the clinical significance and pathophysiology are unknown, it has been proposed that anti-Aβimmunotherapy may affect blood-brain barrier (BBB) integrity.

OBJECTIVE

To examine vascular integrity in aged (12-16 months) PDAPP and wild type mice (WT), we performed a series of longitudinal in vivo MRI studies.

METHODS

Mice were treated on a weekly basis using anti-Aβimmunotherapy (3D6) and follow up was done longitudinally from 1-12 weeks after treatment. BBB-integrity was assessed using both visual assessment of T1-weighted scans and repeated T1 mapping in combination with gadolinium (Gd-DOTA).

RESULTS

A subset of 3D6 treated PDAPP mice displayed numerous BBB disruptions, whereas WT and saline-treated PDAPP mice showed intact BBB integrity under the conditions tested. In addition, the contrast induced decrease in T1 value was observed in the meningeal and midline area. BBB disruption events occurred early during treatment (between 1 and 5 weeks), were transient, and resolved quickly. Finally, BBB-leakages associated with microhemorrhages were confirmed by Perls'Prussian blue histopathological analysis.

CONCLUSION

Our preclinical findings support the hypothesis that 3D6 leads to transient leakage from amyloid-positive vessels. The current study has provided valuable insights on the time course of vascular alterations during immunization treatment and supports further research in relation to the nature of ARIA and the utility of in vivo repeated T1 MRI as a translational tool.

Modelling and sample size reestimation for longitudinal count data with incomplete follow up

We consider modelling and inference as well as sample size estimation and reestimation for clinical trials with longitudinal count data as outcomes. Our approach is general but is rooted in design and analysis of multiple sclerosis trials where lesion counts obtained by magnetic resonance imaging are important endpoints. We adopt a binomial thinning model that allows for correlated counts with marginal Poisson or negative binomial distributions. Methods for sample size planning and blinded sample size reestimation for randomised controlled clinical trials with such outcomes are developed. The models and approaches are applicable to data with incomplete observations. A simulation study is conducted to assess the effectiveness of sample size estimation and blinded sample size reestimation methods. Sample sizes attained through these procedures are shown to maintain the desired study power without inflating the type I error. Data from a recent trial in patients with secondary progressive multiple sclerosis illustrate the modelling approach.

Seeing is believing: in vivo evolution of multiple sclerosis pathology with magnetic resonance

Multiple sclerosis (MS) is considered a prototypical inflammatory autoimmune disease of the central nervous system that affects both myelin and axon. One of the most challenging aspects of MS is understanding the nature and mechanism of tissue injury because inflammation, demyelination, axonal degeneration, microvascular injury, and atrophy are all identified in histopathologic studies. Magnetic resonance (MR) imaging provides an in vivo examination of the brain that directly defines the extent of the pathology. In recent years, extensive MR studies have had a major impact on MS not only in making an early diagnosis but also in understanding of the disease. By exploiting the natural history and histopathologic correlation, conventional and various novel quantitative MR techniques have demonstrated the ability to image underlying pathological processes in MS. This review examines the role of different MR techniques in going beyond anatomical imaging and produces a more comprehensive overview of the pathophysiological changes which occur and evolve in MS.

Zinc-ion binding and cytokine activity regulation pathways predicts outcome in relapsing-remitting multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease characterized by an unpredictable clinical course with intermittent relapses that lead over time to significant neurological disability. Clinical and radiological variables are limited in the ability to predict disease course. Peripheral blood genome scale analyses were used to characterize MS patients with different disease types, but not for prediction of outcome. Using complementary-DNA microarrays we studied peripheral-blood gene expression patterns in 53 relapsing-remitting MS patients. Patients were classified into good, intermediate and poor clinical outcome established after 2-year follow-up. A training set of 26 samples was used to identify clinical outcome differentiating gene-expression signature. Supervised learning and feature selection algorithms were applied to identify a predictive signature that was validated in an independent group of 27 patients. Key genes within the predictive signature were confirmed by quantitative reverse transcription-polymerase chain reaction in an additional 10 patients. The analysis identified 431 differentiating genes between patients with good and poor clinical outcome (change in neurological disability by the expanded disability status scale was -0.33 +/- 0.24 and 1.6 +/- 0.35, P = 0.0002, total number of relapses were 0 and 1.80 +/- 0.35, P = 0.00009, respectively). An optimal set of 29 genes was depicted as a clinical outcome predictive gene expression signature and classified appropriately 88.9% of patients. This predictive signature was enriched by genes related biologically to zinc-ion binding and cytokine activity regulation pathways involved in inflammation and apoptosis. Our findings provide a basis for monitoring patients by prediction of disease outcome and can be incorporated into clinical decision-making in relapsing-remitting MS.

The role of MRI in the diagnosis of MS

Magnetic resonance imaging (MRI) is the most widely used imaging technique in the investigation of multiple sclerosis (MS). Although MS remains a clinical diagnosis, MRI has become an invaluable tool in understanding and monitoring the disease, and is commonly used to confirm the clinical diagnosis. Various imaging techniques can be used but T2-weighted brain imaging remains the standard tool. The officially endorsed imaging criteria for MS places greater emphasis on the spatial and temporal distribution of lesions than on their individual appearance. This review focuses on the more typical findings in MS, and considers the current role of MRI in the diagnosis.

Dose and Frequency of Administration of Interferon-?? Affect its Efficacy in Multiple Sclerosis

Data reviewed in this article demonstrate that both interferon-beta-1a (IFNbeta-1a) and interferon-beta-1b (IFNbeta-1b) show a dose-response relationship in multiple sclerosis at current clinical doses. Moreover, the efficacy of these therapies is probably dependent on their frequent administration to maintain optimal levels of biological effect. These results differ from the conclusions of a recent review of data comparing two doses of IFNbeta-1a, given intramuscularly once weekly, that showed no difference in efficacy between the two doses. This and other results were interpreted to indicate that the current dose of this product (30microg intramuscularly once weekly) is optimal. However, the data reviewed here indicate that the efficacy of IFNbeta differs depending on the features of the dose regimen, including total dose, route and frequency of administration. Direct comparative data indicate that 44microg given subcutaneously three times weekly is more effective on clinical and magnetic resonance imaging measures, at least up to 48 weeks of therapy, compared with 30microg intramuscularly once weekly; risk-benefit favours 44mug three times weekly over 30mug once weekly.

MRI measurement of blood-brain barrier permeability following spontaneous reperfusion in the starch microsphere model of ischemia

Quantification of the acute increases in blood-brain barrier (BBB) permeability that occur subsequent to experimental ischemic injury has been limited to single time-point, invasive methodologies. Although permeability can be qualitatively assessed to visualise regional changes during sequential studies on the same animal using contrast-enhanced magnetic resonance imaging (MRI), quantitative information on the magnitude of change is required to compare barrier function during sequential studies on the same animal or between different animals. Recently, improvements in MRI tracer kinetic models and in MR hardware design mean that an estimate of permeability in vivo can now be obtained with acceptable accuracy and precision. We report here the use of such methods to study acute changes following spontaneous reperfusion in an animal model of ischemia. We have obtained estimates of BBB permeability following spontaneous reperfusion, subsequent to forebrain ischemia by unilateral carotid injection of starch microspheres in the rat. T2*-weighted and diffusion-trace imaging were used to monitor the initial reduction in CBF and the time-course of ischemia, respectively. Following reperfusion, an intraveneous bolus of dimeglumine gadopentetate (Gd-DTPA) and horseradish peroxidase (HRP) was given during a continuous acquisition of T1 maps with a 48 s temporal resolution. Permeability maps were constructed using a 4-compartment model; K(trans), the permeability-surface area product of the capillary walls was estimated to be 9.2 +/- 0.6 x 10(-4) min(-1) in the cortex. Visualisation of the regional extent of HRP extravasation on histological sections following termination of the experiment demonstrated very little correspondence to the region of Gd-DTPA leakage. Quantitative MRI assessment of BBB permeability following ischemia-reperfusion is consistent with published values obtained by invasive methods. Differences between Gd-DTPA-enhancement and HRP may reflect differences in the molecular size of the tracers.

Evolving concepts in the pathogenesis of multiple sclerosis and their therapeutic implications

Recent evidence suggests that multiple sclerosis (MS) is a continuously active neuropathologic process, even during the subclinical relapsing/remitting phase of the disease. Patients commonly feel well and function without disability for many years, experiencing only occasional relapses and nondisabling symptoms. In time, many evolve into a pattern of continuously progressive neurologic disability termed secondary progressive MS (SP-MS). SP-MS is hypothesized to occur once disease severity has exceeded a threshold. Above that threshold, compensatory mechanisms are inadequate to maintain normal function, and further disease progression is accompanied by progressively worsening disability. Inflammation dominates the early stage of disease. Progressive axonal pathology may underlie clinical disease progression in later stages. These concepts have important implications related to the diagnosis, methods for patient follow-up, type and timing of disease therapy, and the testing of neuroprotective drugs in MS.

Interferon beta-1a for optic neuritis patients at high risk for multiple sclerosis

PURPOSE

To evaluate the effect of treatment with interferon beta-1a (Avonex) initiated at the time of a first episode of optic neuritis in patients at high risk for multiple sclerosis (MS).

DESIGN

Randomized clinical trial.

METHODS

Prospective.

SETTING

Fifty clinical centers throughout the US and Canada.

STUDY POPULATION

After the onset of a first episode of optic neuritis treated with intravenous and oral corticosteroids, 192 patients with brain magnetic resonance imaging (MRI) evidence of subclinical demyelination were randomly assigned to receive weekly intramuscular injections of 30 microg interferon beta-1a or placebo.

MAIN OUTCOME MEASURE

The study outcomes were the development of clinically definite MS within 3 years of follow-up and brain MRI changes at 6, 12, and 18 months.

RESULTS

The rates of clinically definite MS and of a combined MS/MRI outcome were lower in the interferon beta-1a group than in the placebo group (adjusted rate ratios 0.58, 95% confidence interval 0.34 to 1.00; and 0.50, 95% confidence interval 0.34 to 0.73, respectively). Compared with the placebo group, on the 18-month brain MRI the interferon beta-1a group had a smaller change from baseline in T2 lesion volume (P =.02), fewer new or enlarging T2 lesions (P <.001), and a lower frequency of Gd-enhancing lesions (P <.001).

CONCLUSION

The clinical and brain MRI results of this trial support initiating interferon beta-1a treatment at the time of a first episode of optic neuritis occurring in patients at high risk for MS based on the presence of subclinical brain MRI lesions.

The accuracy of whole brain N-acetylaspartate quantification

A non-localizing pulse sequence to quantify the total amount of N-acetylaspartate (NAA) in the whole brain (WBNAA) was introduced recently [Magn. Reson. Med. 40, 684-689 (1998)]. However, it is known that regional magnetic field inhomogeneities, deltaB0s, arising from susceptibility differences at tissue interfaces, shift and broaden local resonances to outside the integration window, leading to an underestimation of the true amount of NAA in the entire brain. To quantify the upper limit of this loss, the whole-head proton MR spectrum (1H-MRS) of the water was integrated over the same frequency width as the NAA. The ratio of this area/total-water-line was 75 +/- 5% in 5 volunteers. The procedure was repeated with the brain-only water peak, obtained by summing signals only from voxels within that organ from a three-dimensional chemical-shift-imaging (3D CSI) set. It indicated that <10% of the water signal loss occurred in the brain. Therefore, by analogy, WBNAA accounts for >90% of that metabolite.

Brain atrophy in relapsing multiple sclerosis: relationship to relapses, EDSS, and treatment with interferon beta-1a

Brain atrophy is a relevant surrogate marker of the disease process in multiple sclerosis (MS) because it represents the net effect of various pathological processes leading to brain tissue loss. There are various approaches to quantifying central nervous system atrophy in MS. We have focused on a normalized measure of whole brain atrophy, the brain parenchymal fraction (BPF). BPF is defined as the brain parenchymal volume, divided by the volume within the surface of the brain. We applied this method to an MRI data set generated during a phase III clinical trial of interferon beta-1a (AVONEX). The purpose of the current study is to further explore clinical and MRI correlates of the BPF, particularly as they relate to relapse rate and Kurtzke's Expanded Disability Status Score (EDSS); and to further explore the therapeutic effects observed in interferon beta-1a recipients. Of all demographic and disease measures in the clinical trial data base, T2 lesion volume most closely correlated with BPF in cross sectional studies, and was the baseline factor most closely correlated with progressive brain atrophy in the subsequent 2 years. We also observed that change in T2 lesion volume was the disease measure most closely correlated with change in BPF during 2 years of observation. Of interest, relapse number and EDSS change during 2 years were only weakly correlated with BPF change during the same period. Disability progression, defined as sustained worsening of at least 1.0 EDSS points from baseline, persisting at least 6 months, was associated with significantly greater brain atrophy progression. We observed a therapeutic effect of interferon beta-1a in the second year of the clinical trial, and this beneficial effect was not accounted for by change in gadolinium enhanced lesion volume, or by corticosteroid medication within 40 days of the final MRI scan. The BPF is an informative surrogate marker for destructive pathological processes in relaping MS patients, and is useful in demonstrating treatment effects in controlled clinical trials. The significance of progressive brain atrophy during relapsing MS will be assessed by measuring clinical and MRI changes in prospective follow up studies.

A longitudinal study of T1 hypointense lesions in relapsing MS: MSCRG trial of interferon beta-1a. Multiple Sclerosis Collaborative Research Group

BACKGROUND

T1 hypointense lesions (T1 black holes) are focal areas of relatively severe CNS tissue damage detected by MRI in patients with MS.

OBJECTIVE

To determine the natural history of T1 hypointense lesions in relapsing MS and the utility of T1 hypointense lesions as outcome measures in MS clinical trials.

METHODS

MR studies were from the Multiple Sclerosis Collaborative Research Group trial. Longitudinal results are reported in 80 placebo- and 80 interferon beta-1a (IFNbeta-1a)-treated patients with mild to moderate disability relapsing-remitting MS.

RESULTS

There was a small but significant correlation between T1 hypointense lesion volume and disability at baseline and on trial (r = 0.22, r = 0.28). In placebo patients there was a 29.2% increase in the mean volume of T1 hypointense lesions (median 124.5 mm3) over 2 years (p < 0.001 for change from baseline), as compared to an 11.8% increase (median 40 mm3) in the IFNbeta-1a-treated patients (change from baseline not significant). These treatment group comparisons did not quite reach significance. The most significant contributor to change in T1 hypointense lesions was the baseline number of enhancing lesions (model r2 = 0.554). Placebo patients with more active disease, defined by enhancing lesions at baseline, were the only group to show a significant increase in T1 hypointense lesion volume from baseline.

CONCLUSION

The development of T1 hypointense lesions is strongly influenced by prior inflammatory disease activity, as indicated by enhancing lesions. These results suggest that treatment with once weekly IM IFNbeta-1a (30 mcg) slows the 2-year accumulation of these lesions in the brain.

Bimonthly cranial MRI activity following an isolated monosymptomatic demyelinating syndrome: potential outcome measures for future multiple sclerosis 'prevention' trials

Patients with characteristic white matter lesions on MR imaging are at increased risk for the subsequent development of clinically definite MS (CDMS) following an isolated, monosymptomatic demyelinating syndrome (IMDS). These MR positive first-onset patients are thus candidates for MS prevention trials. Seven consecutive patients with IMDS and two or more periventricular and/or oval lesions on MR imaging were enrolled into a prospective trial based on serial T2-weighted and enhanced MR imaging at two month intervals for 12 - 15 months. Forty-seven new enhancing lesions were detected with triple dose MR contrast compared to 31 lesions using the standard dose. Four of the seven patients accounted for 98% of all enhancing lesions in this study, while the remaining three patients showed little MRI or clinical disease activity. New T2 lesion counts correlated strongly with enhanced lesion counts (r=0.82 - 0.98). We detected 49 new T2-hyperintense (T2) lesions based on short-interval (2 monthly) follow-up, and 31 new T2-lesions comparing exit and entry examinations. These results suggest several potential MR-based strategies for evaluating first onset patients in a phase III MS prevention trial. Since these patients have a small average T2-lesion load, it is quite easy to visually detect new T2 lesions. As a result, at a bimonthly study interval, T2-weighted lesion analysis is an effective measure of cumulative disease activity, provided high-resolution T2-weighted imaging studies are acquired to quantitate new T2-lesions. Enhanced lesion activity remains an important measure of blood - brain - barrier breakdown and may predict short term MRI and clinical disease activity in IMDS patients.

From enhancing lesions to brain atrophy in relapsing MS

Based on observations from MR imaging studies, the natural history of the MS lesion appears to be progression from an acute enhancing lesion, corresponding to the early inflammatory stage, with evolution to a chronic T2 hyperintense lesion, which is the non-specific 'footprint' of the prior event. In addition to accumulation of these relatively non-specific lesions, we find in longitudinal evaluations that patients with only mild to modest disability are already developing significant cerebral atrophy. Atrophy, particularly that resulting from volume loss around the third ventricle, appears to be predicted by the presence of prior temporally and anatomically distant enhancing lesions. One can speculate that the initial enhancing-inflammatory lesion events in the brain, place into motion, at an early stage, the processes that ultimately lead to cerebral atrophy, and these processes may include early axonal injury.

Total brain N-acetylaspartate concentration in normal, age-grouped females: quantitation with non-echo proton NMR spectroscopy

The intra-individual and inter-individual variations of the global N-acetylaspartate (NAA) concentration were measured in a cohort of five 42+/-5 year-old normal females. The total NAA signal from the whole head was obtained with non-localized non-echo proton spectroscopy (1H-MRS) and converted into absolute mole amounts using phantom replacement. Since NAA is assumed to be present only in neurons, its concentration was obtained by dividing these mole amounts with the brains' volume, calculated from high resolution MRI. The key feature of the procedure is its near-complete suppression of the intense subcutaneous and bone marrow lipids' signals, whose chemical shifts neighbor and underlay the NAA. This was achieved by exploiting the lipids' much shorter T1s, compared to that of NAA, for destructive interference of their signals in co-addition following alternating, nonselective 180 degrees inversions. The average global, inter-individual NAA concentration in that group was found to be 10.63 mM with a 95% confidence interval of 10.43-10.82 mM.

Magnetic resonance studies of intramuscular interferon beta-1a for relapsing multiple sclerosis. The Multiple Sclerosis Collaborative Research Group

The Multiple Sclerosis Collaborative Research Group trial was a double-blind, randomized, multicenter, phase III, placebo-controlled study of interferon beta-1a (IFNbeta-1a; AVONEX) in relapsing forms of multiple sclerosis. Initial magnetic resonance imaging results have been published; this report provides additional results. Treatment with IFNbeta-1a, 30 microg once weekly by intramuscular injection, resulted in a significant decrease in the number of new, enlarging, and new plus enlarging T2 lesions over 2 years. The median increase in T2 lesion volume in placebo and IFNbeta-1a patients was 455 and 152 mm3, respectively, at 1 year and 1,410 and 628 mm3 at 2 years, although the treatment group differences did not reach statistical significance. For active patients, defined as those with gadolinium enhancement at baseline, the median change in T2 lesion volume in placebo and IFNbeta-1a patients was 1,578 and -12 mm3 and 2,980 and 1,285 mm3 at 1 and 2 years, respectively. Except for a minimal correlation of 0.30 between relapse rate and the number of gadolinium-enhanced lesions, correlations between MR and clinical measures at baseline and throughout the study were in general poor. Once weekly intramuscular IFNbeta-1a appears to impede the development of multiple sclerosis lesions at an early stage and has a favorable impact on the long-term sequelae of these inflammatory events as indicated by the slowed accumulation of T2 lesions.