The transverse magnetisation decay characteristics of longstanding lesions and normal-appearing white matter in multiple sclerosis

Magnetic resonance spectroscopic findings of chronic lesions in two subtypes of multiple sclerosis: primary progressive versus relapsing remitting

Background

Multiple sclerosis (MS) is a highly prevalent cause of neurological disability and has different clinical subtypes with potentially different underlying pathologies. Differentiation of primary progressive multiple sclerosis (PPMS) from relapsing remitting multiple sclerosis (RRMS) could be difficult especially in its early phases.

Objectives

We compared brain metabolite concentrations and ratios in patients with PPMS and RRMS by magnetic resonance spectroscopic imaging (MRSI).

Patients and Methods

Thirty patients with definite MS (15 with RRMS and 15 with PPMS) underwent MRSI and their non-enhancing lesion metabolites were measured. N-acetyl aspartate (NAA), Creatine (Cr), Choline (Cho), NAA/Cr and NAA/Cho were measured and compared between the two MS subtypes.

Results

When the two MS groups were compared together, we found that Cr was significantly increased (P value=0.008) and NAA/Cr was significantly decreased (P value=0.03) in non-enhancing lesions in PPMS compared with RRMS. There was no significant difference in NAA, Cho or NAA/Cho between the two MS subtypes.

Conclusion

MRS is a potential way to differentiate PPMS and RRMS.

MR relaxation in multiple sclerosis

This article provides an overview of relaxation times and their application to normal brain and brain and cord affected by multiple sclerosis. The goal is to provide readers with an intuitive understanding of what influences relaxation times, how relaxation times can be accurately measured, and how they provide specific information about the pathology of MS. The article summarizes significant results from relaxation time studies in the normal human brain and cord and from people who have multiple sclerosis. It also reports on studies that have compared relaxation time results with results from other MR techniques.

Quantification of subtle blood-brain barrier disruption in non-enhancing lesions in multiple sclerosis: a study of disease and lesion subtypes

Few attempts have been made to detect subtle blood-brain barrier (BBB) leakage in visibly non-enhancing MRI lesions in multiple sclerosis (MS). For 19 patients, longitudinal relaxation time (T1) maps were generated from MRI scans obtained before, and at 20, 40 and 60 minutes after injection of gadolinium (Gd)-DTPA (0.3 mmol/kg). Regions of interest (ROI) were placed around non-enhancing lesions, and in paired contralateral normal appearing brain tissue (NABT). Post-Gd rate of R1 (=1/T1) rise (ΔR1/Δt), was used to quantify leakage. ΔR1/Δt was greater in lesions than paired NABT ( P ≤ 0.001 at all post-Gd timepoints). ΔR1/Δt was greater in T1 hypointense than isointense lesions ( P = 0.001 and 0.01 for first and second timepoints respectively), and negatively related to lesion cross sectional area ( P ≤ 0.001 at all post-Gd timepoints). Relapsing remitting (RRMS) lesions had a greater initial ΔR1/Δt than secondary progressive (SPMS) lesions ( P = 0.04), but this was not seen in subsequent timepoints. ΔR1/Δt in visibly enhancing lesions was significantly greater than in visibly non-enhancing lesions, with no overlap in the normal ranges of the two populations. Subtle BBB leakage is a consistent feature in non-enhancing lesions, and is distinct from the overt BBB leakage observed in visibly enhancing lesions. It is detectable using quantitative contrast-enhanced MRI. It is apparent in all clinical and lesion subtypes studied, and greater in T1 hypointense and smaller lesions. Larger initial ΔR1/Δt in RRMS than SPMS lesions may reflect differences in blood volume rather than BBB leakage. Multiple Sclerosis 2007; 13: 884—894. http://msj.sagepub.com

A study of subtle blood brain barrier disruption in a placebo-controlled trial of natalizumab in relapsing remitting multiple sclerosis

Natalizumab, an anti-alpha4 integrin antibody, significantly reduces the number of visibly enhancing multiple sclerosis (MS) lesions. In this substudy of a 2-year trial of natalizumab monotherapy versus placebo, contrast-enhanced imaging investigated for subtle blood brain barrier (BBB) leakage in relapsing remitting (RRMS) patients, and whether such leakage is modified by natalizumab. After 24 weeks on treatment, 40 patients from 3 centres (27 on natalizumab and 13 on placebo) were studied. T1 weighted images were obtained before and at set timepoints up to 46 minutes after gadolinium (Gd)-DTPA (0.3 mmol/kg to 18 patients, 0.15 mmol/kg to 22). Paired regions of interest were placed around non-enhancing lesions and contralateral normal appearing white matter (NAWM). BBB leakage was inferred through post-Gd T1 weighted signal intensity (SI) change. SI change was greater in T2 non-enhancing lesions than paired NAWM at all timepoints (P<0.005), indicating BBB leakage in lesions. No significant difference in inferred BBB leakage was observed between treatment arms as measured by SI change of lesions (P>0.05 for all timepoints, joint test P=0.24), or in SI change of NAWM (joint test P=0.37). T1 hypointense and isointense lesions exhibited similar SI changes (joint test P=0.12). There is evidence of a subtle BBB leakage within visibly non-enhancing lesions in RRMS that was not modified by alpha4 integrin blockade in this substudy cohort.

Quantification of central motor conduction deficits in multiple sclerosis patients before and after treatment of acute exacerbation by methylprednisolone

OBJECTIVE

To compare the effects of intravenous methylprednisolone (IVMP) in patients with relapsing-remitting (RR-MS), secondary progressive (SP-MS), and primary progressive multiple sclerosis (PP-MS).

METHODS

Clinical and neurophysiological follow up was undertaken in 24 RR-MS, eight SP-MS, and nine PP-MS patients receiving Solu-Medrol 500 mg/d over five days for exacerbations involving the motor system. Motor evoked potentials (MEPs) were used to measure central motor conduction time (CMCT) and the triple stimulation technique (TST) was applied to assess conduction deficits. The TST allows accurate quantification of the number of conducting central motor neurones, expressed by the TST amplitude ratio.

RESULTS

There was a significant increase in TST amplitude ratio in RR-MS (p<0.001) and SP-MS patients (p<0.02) at day 5, paralleling an increase in muscle force. TST amplitude ratio and muscle force remained stable at two months. In PP-MS, TST amplitude ratio and muscle force did not change. CMCT did not change significantly in any of the three groups.

CONCLUSIONS

In RR-MS and SP-MS, IVMP is followed by a prompt increase in conducting central motor neurones paralleled by improvement in muscle force, which most probably reflects partial resolution of central conduction block. The lack of similar clinical and neurophysiological changes in PP-MS corroborates previous clinical reports on limited IVMP efficacy in this patient group and points to pathophysiological differences underlying exacerbations in PP-MS.

Technical note: the comparison of hypointense lesions from 'pseudo-T1' and T1-weighted images in secondary progressive multiple sclerosis

There is a large historical database of dual-echo conventional spin-echo (CSE) magnetic resonance images in multiple sderosis (MS). If new analysis techniques can be developed then this database could provide valuable information. We have investigated a technique in which the late echo of a dual-echo data set is subtracted from the corresponding early echoyielding images, which appear qualitatively similar to T1-weighted images. This study investigated whether the hypointense lesions on the 'pseudo-T1' images (created as described above) were related to hypointense lesions on conventional T1-weighted images. The hypointense lesion areas were measured by a blinded observer using a computer-assisted contouring technique applied to pseudo-T1 and T1-weighted CSE images obtained from 17 patients with secondary progressive MS (SPMS). The mean hypointense lesion area from T1-weighted images was 2218 +/- 2072 mm2, compared to 1426 +/- 1353 mm2 from pseudo-T1 images (p = 0.008). There was, however, a strong correlation between the values obtained from the two sets of images (r = 0.93, p < 0.001). The strong correlation between the values obtained from the two sets of images suggests that pseudo-T1 images may be useful to investigate a subgroup of more destructive lesions in MS from historical databases and in future prospective studies when imaging time is limited.

Primary progressive multiple sclerosis: increasing clarity but many unanswered questions

Heterogeneity in the clinical course of multiple sclerosis (MS) is well recognised and patients following a primary progressive course, 10-15% of the MS population, have a distinct clinical and paraclinical phenotype. This review examines recent advances in our understanding of this subgroup of patients and examines the new criteria to be applied in diagnosis. It also highlights developments in genetic, immunological, magnetic resonance and pathological aspects of the disease, whilst also outlining the results of recent therapeutic trials.

Biexponential T2 relaxation time analysis of the brain: correlation with magnetization transfer ratio

RATIONALE AND OBJECTIVES

To measure T2 relaxation times of normal white and gray matter using a novel CPMG sequence and investigate if any correlation exists between magnetization transfer ratio (MTR) and T2 relaxation-related parameters.

MATERIALS AND METHODS

Seventeen normal volunteers participated on this study. A single-slice 32-echo sequence was used to calculate the T2 relaxation time of frontal and occipital white matter and cortical gray matter. T2 relaxation analysis included monoexponential and biexponential fitting whereas an F test was used to determine if biexponential fitting was statistically more accurate than monoexponential fitting. Short and long T2 constants were calculated as well as the signal fractions of each pool. MTR calculations were based on a three-dimensional gradient echo (3D FFE) proton density weighted sequence with and without an on-resonance composite prepulse. MTR and T2 relaxation times were calculated and linear regression analysis was applied.

RESULTS

Biexponential fitting was more accurate comparing with monoexponential fitting in all WM and GM regions (F > 2.47, P < 0.01). Mean values of short T2 constant for frontal white matter (fWM), occipital white matter (oWM) and gray matter (GM) were 8.10, 9.36, and 22.23 milliseconds, respectively, whereas the mean values of long T2 constant were 85.1, 93.02, and 118.72 milliseconds, respectively. Mean restricted water percentages (RWP)-corresponding to the signal fraction of the protons with short T2-for the fWM, oWM, and GM were 22.01%, 23.36%, and 18.7%. Mean free water percentages (FWP)-corresponding to the signal fraction of the protons with long T2-for the fWM, oWM and GM were 77.99%, 76.64%, and 81.3%. Mean MTR values for fWM, oWM and GM were 68.4%, 68.2%, and 61.3%, respectively. No significant correlation was found in fWM and oWM between MTR and RWP, short and long T2 components while a moderate correlation existed in GM between MTR and RWP (r = 0.57; P = 0.02), MTR and short T2 component (r = -0.69; P = 0.004) and MTR and long T2 component (r = -0.62; P = 0.012).

CONCLUSIONS

Two proton pools with different T2 decay characteristics can be separated in normal gray and white matter when using a multiecho sequence with short echo spacing. MTR and T2 relaxation times were significantly correlated in gray matter and the combination of both types of measurements may be helpful in studying myelin related disorders.

Normal-appearing white matter in multiple sclerosis has heterogeneous, diffusely prolonged T(2)

T(2) relaxation in normal-appearing white matter (NAWM) of multiple sclerosis (MS) patients was reexamined using more complete sampling and analysis of decay curves, and to assess focal vs. diffuse abnormalities. Nine MS patients and 10 controls were scanned using a single-slice 32-echo pulse sequence with a 10-ms echo spacing. Decay curves from outlined white and gray matter structures were analyzed using non-negative least-squares (NNLS). Resulting T(2) distributions were each summarized by the geometric mean T(2), T(2). Different white matter structures had different mean (over the subjects in a group) T(2). Mean T(2) in NAWM was always greater than that of controls. Differences were not caused by a few voxels with extreme T(2) (i.e., focal lesions), but rather by shifts of the entire T(2) distribution (diffuse prolongation). This T(2) increase suggests diffuse myelin or axonal pathology.

Variations in T1 and T2 relaxation times of normal appearing white matter and lesions in multiple sclerosis

OBJECTIVE

To investigate the variation in T1 and T2 relaxation times of normal appearing white matter (NAWM) and lesions in multiple sclerosis (MS) throughout the brain.

BACKGROUND

The magnetic resonance imaging (MRI) sequence fast FLAIR (fluid attenuated inversion recovery) has demonstrated overall increased lesion detection when compared to conventional or fast spin echo (FSE) but fewer lesions in the posterior fossa and spinal cord. The reasons for this are unknown, but may be due to variations in the T1 and T2 relaxation times within NAWM and MS lesions.

METHOD

Ten patients and 10 controls underwent MRI of the brain which involved FSE, fast FLAIR and the measurement of T1 and T2 relaxation times.

RESULTS

Of 151 lesions analysed (22 infra-tentorial, 129 supra-tentorial), eight were missed by the fast FLAIR sequence. T1 and T2 relaxation times in normal controls were longer in the infra-tentorial, than supra-tentorial, region. Patient NAWM relaxation times were prolonged compared with control values in both regions. Lesions demonstrated longer relaxation times than either control white matter or patient NAWM in both regions, however this difference was less marked infra-tentorially. The eight posterior fossa lesions not visible on the fast FLAIR sequence were characterised by short T1 and T2 relaxation times which overlapped with the patient NAWM for both T1 and T2 and with control values for T2 relaxation times.

CONCLUSION

Both lesion and NAWM relaxation time characteristics vary throughout the brain. The T1 and T2 relaxation times of infra-tentorial lesions are closer to the relaxation times of local NAWM than supra-tentorial lesions, resulting in reduced contrast between posterior fossa lesions and the background NAWM. Consequently the characteristics of some lesions overlap with those of NAWM resulting in reduced conspicuity. By utilising this information, it may be possible to optimise fast FLAIR sequences to improve infra-tentorial lesion detection.

1H MRSI comparison of white matter and lesions in primary progressive and relapsing-remitting MS

OBJECTIVE

To compare brain metabolite levels in patients with primary progressive (PP) and relapsing remitting (RR) MS and controls.

HYPOTHESES

(1) creatine (Cr), a putative marker of gliosis, is elevated and N-acetylaspartate (NAA), a putative marker of axonal density and functional integrity, is reduced in PPMS lesions and normal appearing white matter (NAWM) compared to control white matter; (2) The pattern of metabolite change in PPMS is different than in RRMS.

METHODS

MRI and proton magnetic resonance spectroscopic imaging (1H MRSI) were collected from 15 PPMS patients, 13 RRMS patients, and 20 controls.

RESULTS

Cr was increased in PPMS NAWM compared to controls (P=0.035), and compared to RRMS NAWM (P=0.038). Cr was increased in focal MRI lesions from PPMS compared to lesions from RRMS (P=0.044) and compared to control white matter (P=0.041). NAA was similarly reduced in PPMS and RRMS NAWM compared to control. NAA was similarly reduced in PPMS and RRMS lesions, compared to control white matter.

CONCLUSIONS

Creatine is higher in PPMS than RRMS NAWM and focal lesions. This observation is consistent with the notion that progressive disability in PPMS reflects increased gliosis and axonal loss whereas disability in RRMS reflects the cumulative effects of acute inflammatory lesions and axonal loss.

Characterization of tissue damage in multiple sclerosis by nuclear magnetic resonance

Nuclear magnetic resonance (NMR) imaging is an established diagnostic medium to diagnose multiple sclerosis (MS). In clinically stable MS patients, NMR detects silent disease activity, which is the reason why it is being used to monitor treatment trials, in which it serves as a secondary outcome parameter. The absence of a clear correlation with clinical disability, the so-called 'clinico-radiological' paradox, and the poor predictive value of NMR prohibit the use of NMR as a primary outcome parameter in clinical trials. This is--among others--a result of the limited histopathological specificity of conventional, or 'T2-weighted' imaging, the most commonly used NMR technique. In this paper we review additional NMR techniques with higher tissue specificity, most of which show marked heterogeneity within NMR-visible lesions, reflecting histopathological heterogeneity. Gadolinium enhancement identifies the early inflammatory phase of lesion development, with active phagocytosis by macrophages. Persistently hypointense lesions on T1-weighted images ('black holes') relate to axonal loss and matrix destruction, and show a better correlation with clinical disability. Marked prolongation of T1 relaxation time correlates with enlargement of the extracellular space, which occurs as a result of axonal loss or oedema. Axonal viability can also be measured using the concentration of N-acetyl aspartate (NAA) using NMR spectroscopy; this technique is also capable of showing lactate and mobile lipids in lesions with active macrophages. The multi-exponential behaviour of T2 relaxation time in brain white matter provides a tool to monitor the myelin water component in MS lesions (short T2 component) as well as the expansion of the extracellular space (long T2 component). Chemical exchange with macromolecules (e.g. myelin) can be measured using magnetization transfer imaging, and correlates with demyelination, axonal loss and matrix destruction. Increased water diffusion has been found in MS lesions (relating to oedema and an expanded extracellular space) and a loss of anisotropy may indicate a loss of fibre orientation (compatible with demyelination). Apart from the histopathological heterogeneity within focal MS lesions, the normal-appearing white matter shows definite abnormalities with all quantifiable NMR techniques. A decrease in the concentration of NAA, decreased magnetization transfer values and prolonged T1 relaxation time values are probably all related to microscopic abnormalities, including axonal damage. This 'invisible' lesion load may constitute a significant proportion of the total lesion load but is not visible on conventional NMR. Similarly, mechanisms for clinical recovery exist, which are not distinguished using MR imaging. Therefore, it is highly unlikely that the clinico-radiological paradox will ever be solved completely. However, NMR provides an opportunity to sequentially measure tissue changes in vivo. Using MR parameters with (presumed) histopathological specificity, the development of (irreversible) tissue damage can be monitored, which perhaps allows the identification of factors that determine lesional outcome in MS. Since the absence of severe tissue destruction is prognostically favourable, NMR monitoring of the extent to which such changes can be prevented by treatment will ultimately benefit the selection of future treatment strategies.

A study of the HLA-DR region in clinical subgroups of multiple sclerosis and its influence on prognosis

OBJECTIVE

To investigate the HLA-DR associations in relapsing-remitting/secondary progressive multiple sclerosis (RR/SPMS) and primary progressive MS (PPMS). The HLA-DR2 allele (or its split, HLA-DRB1*15) is felt to be a risk factor for MS, rather than a genetic marker for the population of origin. Some studies have indicated a different HLA-DR antigen profile in PPMS patients compared with those having an initially relapsing-remitting course, only those with relapsing disease showing an increase in HLA-DR2. Association of PPMS with DR4 has been suggested. Several DR alleles have also been felt to influence the prognosis in MS.

METHODS

Genomic DNA was prepared from peripheral blood of 202 RR/SPMS patients identified in a population-based prevalence study, 102 PPMS patients identified throughout Northern Ireland and 398 normal controls (Nor) matched for the postcode areas of those identified in the prevalence study. Samples were typed for the HLA-DR antigens using polymerase chain reaction (PCR) technology and sequence specific oligonucleotide probes (SSOP).

RESULTS

A high incidence of HLA-DRB1*15 was found in each MS group - PPMS (63.73%), RR/SPMS (66.83%) - compared with normals (32.41%), (PPMS vs. Nor, P<0.0001: RR/SPMS vs. Nor, P<0.0001). HLA-DRB1*04 occurred at a lower incidence in both MS groups compared with controls - RR/SPMS (22%), PPMS (30%), Nor (35%). Overall, highly significant differences existed across the full HLA-DR allele distribution (RR/SPMS vs. Nor, P<0.0001, df=12: PPMS vs. Nor, P=0.0007, df=12). No significant differences existed between PPMS and RR/SPMS (P=0.47, df=12), and the allele distributions in benign and aggressive MS were similar.

CONCLUSIONS

These data suggest that in this population, HLA-DRB1*15 is indeed associated with PPMS and that PPMS has a HLA-DR profile distinct from the normal population but not from those with an initially relapsing-remitting course. No single allele is associated with either a good or poor prognosis.

Raised CSF levels of soluble adhesion molecules across the clinical spectrum of multiple sclerosis

Endothelial activation is considered an important step in multiple sclerosis (MS) lesion formation, elevated cerebrospinal fluid (CSF) and serum levels of certain adhesion molecules being associated with varying stages of disease activity and clinical course. CSF and serum sVCAM-1, sICAM-1, sE-selectin and sL-selectin were measured by ELISA in 16 primary progressive (PPMS), 16 secondary progressive (SPMS) and 43 relapsing-remitting MS patients (RRMS) and compared with 20 inflammatory (IND) and 46 non-inflammatory neurological disease (NIND) controls. CSF sVCAM-1 and sICAM-1 were increased in all MS groups vs. NIND with no significant differences between the MS groups. CSF sE-selectin (p = 0.007) and the sE-selectin index (p = 0.01) were elevated in PPMS vs. RRMS in relapse, whilst serum sE-selectin was significantly raised in PPMS compared to RRMS in remission (p = 0.005), RRMS in relapse (p = 0.004), NIND (p = 0.03) and IND (p = 0.05). Adhesion molecule levels in both progressive MS groups were similar. These results provide evidence for a distinct inflammatory component in PPMS and for immunological heterogeneity between the clinical subgroups of MS.

Clinical study of primary progressive multiple sclerosis in Northern Ireland, UK

OBJECTIVE

To investigate the clinical and demographic characteristics of primary progressive multiple sclerosis (PPMS) in Northern Ireland and to establish a database of such patients for genetic and immunological studies and future therapeutic trials.

METHODS

Diagnosis and categorisation were performed by two neurologists, potential cases being identified from the following sources: neurology outpatient clinics; neurology inpatients; a review of hospital discharges; and an ongoing epidemiological study of multiple sclerosis in Northern Ireland. Only those with a progressive course from onset and a clear history of no prior relapses were accepted. Potential cases were invited for interview and assessment, the minimal record of disability (MRD) being established.

RESULTS

One hundred and eleven cases of PPMS have been identified, 63 women and 48 men (ratio 1.3:1), with a mean age at onset of 39.5 (SD 11.0) (range 17-66)years, and mean disease duration of 13.6 (SD 9.3)years. The mean interval between onset and diagnosis was 4.7 (SD 4.2) years. Nineteen patients (17.1%) did not satisfy the requirements for any category in the Poser criteria. Motor disturbance was the commonest mode of onset (67.6%) with visual loss occurring only rarely at onset (3.6%). Kurtzke EDSS scores were concentrated at the upper end of the scale with a median of 6.0 and levels of unemployment and financial dependence were high.

CONCLUSIONS

PPMS in Northern Ireland has a generally later age at onset, lower female preponderance, and predominantly motor onset compared with other subgroups of multiple sclerosis. The delay to diagnosis reflects the often insidious onset and the nature of the clinical course makes application of the Poser criteria difficult. Levels of neurological impairment, disability, and handicap as measured by the MRD are high.