Journal of the Neurological Sciences 338 (2014) 128–134
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Diffusion tensor MRI alterations of subcortical deep gray matter in clinically isolated syndrome Roberto Cappellani a,b, Niels Bergsland a, Bianca Weinstock-Guttman c, Cheryl Kennedy a, Ellen Carl a, Deepa P. Ramasamy a, Jesper Hagemeier a, Michael G. Dwyer a, Francesco Patti b, Robert Zivadinov a,c,⁎ a b c
Buffalo Neuroimaging Analysis Center, Department of Neurology, State University of New York, Buffalo, NY, USA Department GF Ingrassia, Section of Neurosciences, University of Catania, Italy The Jacobs Neurological Institute, Department of Neurology, University at Buffalo, State University of New York, Buffalo, NY, USA
a r t i c l e
i n f o
Article history: Received 11 June 2013 Received in revised form 13 December 2013 Accepted 19 December 2013 Available online 31 December 2013 Keywords: Clinically isolated syndrome Diffusion tensor imaging Fractional anisotropy Subcortical deep gray matter Normal appearing white matter Lesions
a b s t r a c t Background: Abnormalities in the gray matter (GM) of the brain parenchyma are present early in the course of multiple sclerosis. Objectives: To quantify white matter (WM) and subcortical deep GM (SDGM) alterations in patients with clinically isolated syndrome (CIS) using diffusion tensor imaging (DTI). Materials and methods: 45 CIS patients and 52 healthy controls (HC) were scanned on 3 T MRI. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated, in addition to the estimation of structural brain volume and lesion measurements. Results: FA was significantly lower in CIS patients in the whole brain (p b 0.001), total SDGM (p b 0.001), normal appearing (NA) GM (p = 0.016), thalamus (p = 0.029) putamen (p = 0.036), caudate (p = 0.041) and accumbens nuclei (p = 0.041) compared to HC. No DTI MD or volumetric differences were detected in the brain parenchyma between CIS and HC groups. Normalized lateral ventricular volume was higher in CIS patients compared to HC (p = 0.033). A significant association was detected between the increased T2 lesion number and volume and decreased FA of the NAWM (p = 0.036), but not with FA of NAGM or SDGM structures. Conclusions: Diffuse DTI alterations of GM structures, not associated with lesion formation, are present in CIS patients. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Multiple sclerosis (MS) is a demyelinating and neurodegenerative chronic disease of the central nervous system (CNS) characterized by appearance of focal white matter (WM) lesions and the development of tissue injury [1]. Conventional magnetic resonance imaging (MRI) is an important tool not only for determining the early diagnosis of MS [2], but also for monitoring of disease progression [3]. However, pathology outside of the focal WM and gray matter (GM) lesions, in so-called “normal appearing” (NA) WM and NAGM, remains largely undetected by conventional MRI [4–6]. This could explain why the association between MRI visible abnormalities and MS clinical disability is weak [7]. Diffusion tensor imaging (DTI) is an advanced MRI technique that is widely-used in the investigation of the physiopathology of MS [8]. It allows for the study of microscopic motion of water molecules hindered by cellular structures such as the cell membrane and the axonal cytoskeleton. The disruption of myelin sheaths and axons can result in ⁎ Corresponding author at: Department of Neurology, School of Medicine and Biomedical Sciences, The Jacobs Neurological Institute, 100 High St, Buffalo, NY 14203, USA. Tel.: +1 716 859 7031; fax: +1 716 859 4005. E-mail address:
[email protected] (R. Zivadinov). 0022-510X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jns.2013.12.031
higher water motion leading to increased mean diffusivity (MD) values and a change in the preferential motion that is responsible for decreased fractional anisotropy (FA) values [3,9]. FA and MD are the most frequently used scalar maps of DTI for studying neurological disorders, particularly in demyelinating diseases of the CNS [10]. There is a growing interest to study the extent of cortical and subcortical GM pathology (SDGM) from the earliest clinical stages of MS [11]. The relationship between the appearance of WM lesions and SDGM atrophy in MS patients is not well-understood. A number of independent studies have shown that volume loss of SDGM occurs in the early stage of MS disease [12–17]. However, an important question is whether WM damage contributes to the abnormalities in GM regions through a disconnection mechanism or whether GM and WM tissue alterations are affected independently. Previous research has suggested that cortical GM abnormalities in MS may be secondary to WM damage [18]. To further establish the relationship between SDGM atrophy and WM lesions, some recent studies have utilized DTI to assess the structural WM and GM alterations in clinically isolated syndrome (CIS) patients; however, this did not lead to definitive results [14,19]. Against this background, the aim of the present study was to quantify SDGM alterations by examining associations between DTI parameters, structural volume and lesion measurements in the
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Table 1 Demographic and clinical characteristics of clinically isolated syndrome patients and healthy controls.
Age, yrs, mean (SD) median Sex, female, n (%) Disease duration, yrs, mean (SD) median EDSS, mean (SD) median Heart disease, n (%) Hypertension, n (%) Smoking, n (%) Type 1 diabetes mellitus, n (%) BMI mean (SD) median CIS onset type. n (%) polysymptomatic Monosymptomatic T2 lesion number, mean (SD) median T2 lesion volume, mean (SD) median ≥9 T2 lesions, n (%) T1 Gd lesion number mean (SD) median T1 Gd lesion volume mean (SD) median
CIS (n = 45)
HC (n = 52)
p value
38.6 (10.9) 38 36 (80) 2 (1) 2 1.4 (1.1) 1.5 6 (13.3) 0 (0) 21 (46.6) 0 (0) 27.3 (5.0) 26.4 18 (40) 27 (60) 17.9 (19.7) 12 3.5 (5.1) 2.1 25 (55.5) 0.3 (0.98) 0
41.9 (12.2) 43 34 (65.4) NA NA 9 (17.3) 0 (0) 13 (25.0) 0 (0) 26.8 (5.1) 26.9 NA
0.449 0.594 NA NA 0.907 NA 0.140 NA 0.897 NA
0.2 (0.8) 0 0.01 (0.04) 0 0 (0) NA
p b 0.001 p b 0.001 NA NA
0.04 (0.1) 0
NA
NA
Legend = HC: healthy controls; CIS: clinically isolated syndrome; EDSS: Expanded Disability Status Scale; BMI: body mass index; Gd: gadolinium; and SD: standard deviation. Statistical analysis was performed using Student's t-test for continuous variables and chi-square for categorical variables. Analysis of covariance, adjusted for age, was used for comparison of MRI measures between the groups. All p-values were corrected for multiple comparisons using Benjamini–Hochberg correction. Significant p-values (p b 0.05 after correction) are presented in bold. The lesion volumes are expressed in milliliters.
brain parenchyma of CIS patients and to compare them to healthy controls (HC). 2. Materials and methods 2.1. Subjects Forty-five (45) CIS patients and fifty-two (52) age- and sex-matched HC were included in the study. In CIS patients, the dissemination in space (DIS) and dissemination in time (DIT) was evaluated, according to the McDonald 2010 criteria [2]. Only CIS patients who fulfilled DIS at baseline MRI were included in the study. The CIS patients enrolled in the study were those followed by our Center specialized in demyelinating diseases, after their first clinical presentation, or those referred to our Center for a second opinion. Of the 45 CIS patients participating in the study, the follow-up MRI scans were available for 19 CIS patients after an average of 12 months. Presented analyses are based on the
baseline data, since the follow-up MRI protocols were not standardized. CIS patients underwent full neurological neurologic assessment, including Expanded Disability Status Scale (EDSS) evaluation. Participants were excluded if they had contraindications to MRI examination, had any pre-existing medical conditions known to be associated with brain pathology, had a relapse or were treated with steroids within the month preceding study entry (for the CIS group). The internal Institutional Review Board approved the study protocol and written informed consent was obtained from all participants. 2.2. MRI acquisition All subjects were examined on a 3 T GE Signa Excite HD 12.0 Twin Speed 8-channel scanner (General Electric, Milwaukee, WI), using an 8-channel head and neck (HDNV) coil. MRI sequences included multiplanar dual fast spin-echo (FSE) proton density (PD) and T2 weighted image (WI) as well as fluid attenuated inversion recovery (FLAIR), 3D
Table 2 Structural brain volume measures of clinically isolated syndrome patients and healthy controls. Global and tissue specific brain structures
CIS (n = 45)
HC (n = 52)
p value
NGMV, mean (SD) median NWMV, mean (SD) median NBPV, mean (SD) median NLVV, mean (SD) median NCV, mean (SD) median Subcortical deep gray matter structures Total SDGM, mean (SD) median Caudate, mean (SD) median Putamen, mean (SD) median Globus pallidus, mean (SD) median Thalamus, mean (SD) median Hippocampus, mean (SD) median Amygdala, mean (SD) median Nucleus accumbens, mean (SD) median
792.6 (54.9) 791.2 763.8 (55.9) 753.0 1556.6 (71.2) 1551.8 35.9 (13.2) 34.0 641.7 (45.1) 638.1
774.3 (46.6) 772.0 767.1 (41.8) 769.8 1541.5 (72.9) 1523.2 29.1 (7.6) 27.8 631.6 (39.3) 632.8
0.288 0.923 0.654 0.033 0.575
45.8 (4.1) 45.3 7.0 (1.0) 6.9 9.7 (1.2) 9.8 3.4 (0.3) 3.4 15.1 (1.5) 14.9 7.2 (0.7) 7.2 2.4 (0.3) 2.4 0.8 (0.2) 0.9
45.9 (4.9) 46.1 6.9 (1.1) 6.8 9.8 (1.3) 9.7 3.5 (0.4) 3.5 15.3 (1.6) 15.3 7.1 (0.8) 7.0 2.5 (0.4) 2.4 0.8 (0.2) 0.8
0.888 0.901 0.933 0.621 0.815 0.812 0.904 0.823
Legend = NGMV: normalized gray matter volume; NWMV: normalized white matter volume; NBPV: normalized brain parenchymal volume; NLVV: normalized lateral ventricular volume; NCV: normalized cortical volume; and SDGM: subcortical deep gray matter. Between-group differences were assessed using analysis of covariance, adjusted for age. All p-values were corrected for multiple comparisons using Benjamini–Hochberg correction. Significant p-values (p b 0.05 after correction) are presented in bold. The volumes are expressed in milliliters.
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T1-WI using a fast spoiled gradient echo (FSPGR) with magnetizationprepared inversion recovery (IR) pulse and SE T1-WI both with and without a single dose of intravenous bolus of 0.1 mMol/kg gadolinium (Gd)-DTPA. Pulse sequence characteristics were as follows: all scans were acquired with a 256 × 256 matrix and a 25.6 cm field of view (FOV) for an in-plane resolution of 1 × 1 mm2 with a phase FOV (pFOV) of 75% and one average. Sequence specific parameters were as follows: for the PD/T2: 3-mm thick slices with no gap, echo time (TE) 1/TE2/repetition time (TR) = 12/95/3000 ms, echo train length (ETL) = 14, flip angle (FA) = 90°; for the FLAIR scans, 3-mm thick slices with no gap, TE/inversion time (TI)/TR = 120/2100/8500 ms, FA = 90°; for 3D T1-WI, 1-mm-thick slices with no gap, TE/TI/ TR = 2.8/900/5.9 ms, FA = 10° and for SE T1-WI, 3-mm-thick slices with no gap, TE/TR = 16/600 ms, FA = 90°. An echo-planar DTI sequence was also acquired as part of the MRI protocol. Sequence was acquired with 3-mm thick slices with no gap, a 96 × 96 matrix, a 32 cm FOV and a 75% pFOV, resulting in a voxel size of 3.33 mm × 3.33 mm × 3.00 mm. The sequence used a TE/TR of 81.8/8200 ms, 1 average and an ASSET (parallel imaging) factor of 2. DTI parameters were 15 non-collinear directions with a b-value of 800 s1 mm−2. 2.3. MRI analysis T2 and T1 post-contrast lesion number and volume (LV) were assessed using a semiautomated edge detection contouring/thresholding
technique. [20] Using co-registered T2/PD and FLAIR sequences, the visible T2 lesions were evaluated based on their location in the WM, juxtacortical WM/GM and in the SDGM, however no specific anatomical regional lesion localization was performed. No intracortical GM lesions were evaluated. The SIENAX cross-sectional software tool (version 2.6; http://fsl. fmrib.ox.ac.uk/fsl/fslwiki/SIENA) was used to estimate normalized GM volume (NGMV), normalized WM volume (NWMV), normalized brain parenchymal volume (NBPV), normalized lateral ventricular volume (NLVV) and normalized cortical volume (NCV). Prior to segmentation, the 3D T1 WI was modified using an in-house developed inpainting tool to avoid the impact of T1 hypointensities [20]. To segment SDGM structures, the FIRST tool (version 1.2; http://fsl.fmrib.ox.ac.uk/fsl/ fslwiki/FIRST) was used. Specifically, the thalamus, caudate, putamen, globus pallidus, hippocampus, amygdala and accumbens nucleus were identified in this way. Initial DTI processing was performed using FMRIB's Diffusion Toolbox (FDT) [21,22]. Briefly, raw DTI images were eddy corrected to minimize gradient-related geometric distortions. Then, “dtifit” was used to fit a tensor model at each voxel and scalar maps of FA and MD were created. DTI measures from the SDGM were obtained by first co-registering the b0 image to the 3D T1 using a rigid body (6 degrees of freedom) registration. The resulting transformation matrix was then applied to resample the FA and MD maps into the 3D T1 space, using trilinear interpolation. The SDGM masks obtained from FIRST were then used to
Table 3 Diffusion tensor imaging measures of clinically isolated syndrome patients and healthy controls. p Value
MD (×10−3)
Whole brain, mean (SD) median NAWM, mean (SD) median NAGM, mean (SD) median Subcortical deep gray matter structures Total SDGM, mean (SD) median Caudate, mean (SD) median Putamen, mean (SD) median Globus pallidus, mean (SD) median Thalamus, mean (SD) median Hippocampus, mean (SD) median Amygdala, mean (SD) median Nucleus accumbens, mean (SD) median
CIS (n = 45)
HC (n = 52)
0.98 (0.06) 0.96 0.88 (0.05) 0.87 1.08 (0.08) 1.06
0.99 (0.05) 0.99 0.89 (0.05) 0.88 1.10 (0.07) 1.09
1.0 (0.1) 1.0 1.1 (0.2) 1.1 0.8 (0.04) 0.8 0.8 (0.05) 0.8 1.0 (0.15) 1.0 1.1 (0.2) 1.1 1.0 (0.2) 1.0 0.8 (0.1) 0.8
0.9 (0.1) 0.9 1.1 (0.2) 1.0 0.8 (0.07) 0.8 0.7 (0.09) 0.8 1.0 (0.14) 1.0 1.0 (0.2) 1.1 1.0 (0.2) 1.0 0.8 (0.1) 0.9
FA
p value
CIS (n = 45)
HC (n = 52)
0.597
0.25 (0.01) 0.25
0.692
0.35 (0.03) 0.35 0.15 (0.01) 0.15
0.26 (0.01) 0.26 0.36 (0.03) 0.36 0.16 (0.01) 0.16
0.25 (0.02) 0.25 0.18 (0.03) 0.19 0.25 (0.02) 0.24 0.38 (0.05) 0.39 0.29 (0.02) 0.28 0.20 (0.04) 0.20 0.18 (0.03) 0.18 0.19 (0.03) 0.19
0.27 (0.02) 0.27 0.20 (0.03) 0.20 0.26 (0.03) 0.26 0.40 (0.07) 0.41 0.30 (0.02) 0.31 0.22 (0.07) 0.21 0.20 (0.06) 0.19 0.20 (0.04) 0.20
0.337
0.926
0.890
0.340
0.889
0.717
0.696
0.713
0.437
p b 0.001
0.087
0.016
p b 0.001
0.041
0.036
0.225
0.029
0.266
0.06
0.041
Legend = MD: mean diffusivity; FA: fractional anisotropy; NAWM: normal appearing white matter; NAGM: normal appearing gray matter, SDGM: subcortical deep gray matter; and SD: standard deviation. MD is presented in 103 mm2/s. FA is a unitless measure. Between-group differences were assessed using analysis of covariance, adjusted for age. All p-values were corrected for multiple comparisons using Benjamini–Hochberg correction. Significant p-values (p b 0.05 after correction) are presented in bold.
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calculate DTI measures within the structures. NAWM and NAGM measures were obtained by masking the white WM and GM segmentations with the T2 lesion masks. The resulting segmentations (i.e. without the lesions) were then masked with the MD/FA maps to obtain DTI measures of the NAWM and NAGM. 2.4. Statistical analysis Analyses were conducted using PASW Statistics, version 18.0 (IBM, Somers, New York). Differences between the groups were tested using the chi-square test and Student's t test. Distributions of the data were tested for normality using the Shapiro–Wilk test. MRI measurements were compared using the analysis of covariance, adjusted for age. Spearman correlation analysis was used to assess the relationship between DTI, lesion and structure volume measures. All results were corrected for multiple comparisons using Benjamini–Hochberg correction [23]. A nominal p value b0.05 was regarded as significant, using two-tailed testing. 3. Results All CIS subjects fulfilled DIS on baseline MRI examination and had clinical and MRI manifestations suggestive of a demyelinating disease. Six of the 19 CIS patients, who obtained follow-up evaluation, fulfilled the McDonald 2010 criteria for DIT. None of the CIS patients developed clinically definite MS. No demographic, clinical or MRI differences were found between CIS patients who presented with DIS at baseline MRI scan, and those who developed DIT at the follow-up clinical MRI scan after 12 months. Table 1 shows that the demographic and cardiovascular risk factor characteristics between the two groups were well-matched. The mean age in CIS patients was 38.6 (SD 10.9) years. Thirty-six (80%) of patients were female, with a median EDSS score of 1.5. Of the 45 CIS patients, 27 (60%) had a monosymptomatic onset and 25 (55.5%) showed ≥9 T2 hyperintense lesions. Nineteen patients were on disease-modifying treatment which included interferon-beta (16) and glatiramer acetate (3).
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Table 2 shows global and tissue-specific brain structures as well as normalized volume differences between CIS patients and HC. NLVV was higher in CIS patients compared to HC (p = 0.033) but no other significant differences were found comparing the two groups. To investigate the architecture and integrity of the WM and GM structures, we measured the MD and FA in the whole brain, NAWM, NAGM and in the SDGM (Table 3). FA was significantly decreased in CIS patients in the whole brain (p b 0.001), total SDGM (p b 0.001), NAGM (p = 0.016), thalamus (p = 0.029), putamen (p = 0.036), caudate (p = 0.041) and accumbens nuclei (p = 0.041) compared to HC. No MD differences were detected in the same brain regions between the two groups. Table 4 as well as Figs. 1 and 2 show the correlations between FA variables and lesion and brain structural volume measures. Significant relationships were found between increased T2 lesion number and volume with decreased FA of whole brain (p = 0.036) and NAWM (p = 0.036). In contrast, no significant correlations were observed between increased T2 lesion number and volume and decreased FA of the NAGM and SDGM structures. There were significant correlations between decreased NWMV and decreased FA of whole brain (p = 0.033) and caudate (p = 0.036). No relationship was found between DTI FA of SDGM structures and NCV. No differences between treated and non-treated groups were detected. No significant differences were found when CIS patients were subdivided into those with mono- or poly-symptomatic onset. No differences in the study results were found when excluding 6 CIS patients from the analyses, who developed DIT at the follow-up MRI scan after 12 months.
4. Discussion Tissue loss and foci of demyelination with varying degrees have been described in all cortical layers, SDGM and throughout the WM [20,24]. Cortical and SDGM involvement is a significant contributor to the disease process in MS and it is strongly-related to the disability progression and especially to cognitive impartment [25–28].
Table 4 Correlations between diffusion tensor imaging fractional anisotropy, lesions measures and brain structural volumes in clinically isolated syndrome patients. FA
T2-LN rp
T2-LV rp
T1 Gd-LN rp
T1 Gd- LV rp
NWMV rp
NCV rp
Whole brain
−0.439 0.036 −0.446 0.036 −0.109 0.782 −0.157 0.670 −0.337 0.129 −0.077 0.876 −0.142 0.717 −0.202 0.509 0.093 0.849 0.160 0.759 0.003 0.993
−0.427 0.036 −0.441 0.036 −0.140 0.701 −0.175 0.589 −0.338 0.130 0.051 0.934 −0.027 0.940 −0.274 0.262 0.071 0.881 0.243 0.339 −0.045 0.920
−0.113 0.759 −0.122 0.737 0.004 0.995 −0.044 0.922 −0.041 0.927 0.001 0.999 −0.134 0.708 0.008 0.987 0.013 0.978 0.131 0.712 0.167 0.636
−0.120 0.742 −0.141 0.698 0.018 0.970 −0.028 0.944 −0.038 0.939 0.016 0.970 −0.124 0.735 0.011 0.980 0.035 0.944 0.143 0.706 0.178 0.595
0.424 0.033 0.232 0.385 0.100 0.816 0.064 0.880 0.431 0.036 −0.336 0.129 −0.032 0.946 0.176 0.606 −0.138 0.691 −0.252 0.334 −0.067 0.882
0.058 0.895 0.287 0.232 0.069 0.881 −0.075 0.907 0.025 0.940 −0.296 0.216 −0.328 0.137 0.220 0.441 −0.046 0.925 −0.114 0.759 −0.295 0.211
NAWM NAGM Total SDGM Caudate Putamen Globus pallidus Thalamus Hippocampus Amygdala Nucleus accumbens
Legend = FA: fractional anisotropy; NAWM: normal appearing white matter; NAGM: normal appearing gray matter, SDGM: subcortical deep gray matter; LN: lesion number; LV: lesion volume; NWMV: normalized white matter volume; and NCV: normalized cortical volume. The relationship between MRI measures was assessed using a Spearman correlation analysis. All p-values were corrected for multiple comparisons using Benjamini–Hochberg correction. Significant p-values (p b 0.05 after correction) are presented in bold.
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Fig. 1. Scatter plots between fractional anisotropy (FA) of whole brain (upper row), normal appearing white matter (NAWM, middle row) and normal appearing gray matter (NAGM, bottom row) with normalized cortical volume (left column), normalized white matter volume (middle column) and T2 lesion volume (right column). Significant values are displayed and volumes are reported in millimeter cubes.
The present study used a multimodal MRI approach to investigate specific brain changes in CIS patients. In line with the findings from previous DTI studies performed using different methods of analysis [19,29], the results of this study confirm that widespread DTI alterations, as evidenced by the reduction of FA in the whole brain and NAGM, already occur in CIS patients. In addition, the present study extended these findings by investigating a range of SDGM structures in CIS patients at an early stage of demyelinating disease. Compared to HC, we found significantly decreased FA in the total SDGM, caudate, thalamus, putamen and accumbens nuclei. These observations are in agreement with some previous studies that showed that occult DTI alterations occur well beyond T2 visible lesions in patients with MS [30,31]. One possible explanation for the lack of significant differences in MD measures among CIS patients and HC can be explained by the high cellularity of the GM structures that could restrain, in the presence of microstructural alterations, the movement of molecules. Instead FA is sensitive to the orientation of the fibers that might be altered in this early stage of the disease. These observations are in line with previous studies [14,19]. Although the alterations in the NAWM have been consistently established in patients with MS, there are conflicting results concerning DTI alterations in the NAWM in the CIS. Previous studies detected DTI abnormalities in specific WM tracts in CIS patients [19,29]. In a longitudinal study, DTI alterations were not found in the CIS group compared to
HC at baseline but only after a followup of one year, when most of the patients converted to clinically definite MS [32]. In contrast, another study showed significant DTI abnormalities at baseline in the NAWM of CIS patients with a high risk of developing MS [33]. These results suggest that alterations of DTI occur in specific WM tracts and NAWM in CIS patients with high risk for conversion to MS. In the present study, we also investigated differences in global, tissuespecific and regional brain volumes between CIS patients and HC. We detected an increased NLVV in CIS patients but no significant differences of volume loss were detected in other examined brain structures. While these results are in line with some studies which did not detect global and tissue specific GM and WM atrophy in patients with CIS or at an early-stage of MS [34–36], they are in contrast with an emerging literature that identified reductions of thalamus volume as one of the earliest and most significant signs of SDGM pathology in patients that presented with CIS [17,37,38]. Reduction of thalamus volume is also correlated with the conversion to clinically-definite multiple sclerosis in CIS patients [28,37]. Different studies have established that even in healthy individuals, there are strong correlations between age and volume loss of the SDGM structures, particularly of the thalamus [39,40]. Although no significant age difference among CIS and HC was found in the present study, the HC were approximately three years older than the CIS group, which could contribute to the explanation of current findings.
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Fig. 2. Scatter plots between fractional anisotropy (FA) of total subcortical deep gray matter (upper row) and thalamus (bottom row) with normalized cortical volume (left column), normalized white matter volume (middle column) and T2 lesion volume (right column). Volumes are reported in millimeter cubes.
We also investigated the association among FA of the SDGM and the cortical volume to better understand whether the microstructural alterations of SDGM structures are associated with the axonal loss in the cortex. A previous study concerning DTI alterations in the CIS group found a significant reduction of FA in the thalamus of the patients compared with the HC but no DTI abnormalities were detected in the cortical structures [19]. Interestingly, we found no relationship among DTI measures and NCV loss. These results suggest that the damage of SDGM and cortex are underpinned by distinct pathophysiological processes and thus, could occur both independently and at different stages of the disease. DTI is considered a useful marker of pathologic damage as seen in vivo and post mortem studies of MS subjects [41,42]. It has been demonstrated that during the evolution of disease, there are progressive and widespread DTI alterations and atrophy in WM and GM structures [43]. However, to our knowledge, there are only a few studies that have investigated DTI alterations and volume loss of the SDGM structures in patients with early stage MS in order to explore the relationship between the two [19,44]. The present study suggests that DTI alterations may occur before a significant volume reduction of the SDGM structures in CIS patients are detected; however, only longitudinal studies may shed more light on this important topic. Another interesting result from the present study was the lack of a relationship between T2 lesion measures and the FA measures in the NAGM and SDGM structures. No differences were found in treated and untreated CIS groups. One study found significant correlations between T2–LV and thalamic MD alterations in relapsing–remitting and secondary-progressive patients but no relationship was found with thalamic FA measures [45]. DTI alterations in FA of the GM structures seem to be independent of the degree of lesion burden which is indeed, in-line with other studies [46]. The significant relationship between decreased FA of NAWM and increased T2-LV in the present study highlights a possible link between focal injury due to inflammatory and demyelinating lesions and microstructural alteration. Such a relationship was not observed among HC in our study, further strengthening our findings.
The present study is not without limitations. CIS patients were not selected immediately at the time of their first clinical onset but were evaluated approximately two years after the first clinical event. One of the main reasons may be that almost half of the patients participating in this study underwent a neurological and an MRI examination in our center as a second opinion concerning their CIS disease status. Another limitation is that the follow-up data regarding DIT and clinically definite MS development were available only for 19 CIS patients after an average period of 12 months. Of these, 6 CIS patients developed DIT at the follow-up MRI scan at 12 months. Although no demographic, clinical or MRI differences were detected at baseline between CIS patients who presented with DIS and those who developed DIT at the followup MRI scan at 12 months, there were three CIS patients who presented with higher T2-LV at baseline. Because the CIS cohort enrolled in the current study was not entirely homogenous, the analyses were repeated by excluding these 6 CIS patients from the study, which did not influence the study findings. Consequently, only the results of the entire study cohort were presented. Because the analysis of the relationship between T2 lesion appearance and DTI alterations was cross-sectional, we were not able to discern if the alterations of the SDGM structures are secondary or independent to WM injury, and therefore only longitudinal studies investigating DTI abnormalities and T2 lesions in afferent and efferent projections into specific SDGM structures will be able to answer that question. One study that included 24 patients with CIS explored whether the association between WM lesion and thalamic atrophy is related to connectivity of these fibers [14]. The authors suggested that focal MS lesions in thalamocortical WM projections could, in part, directly lead to thalamic neuronal and volume loss. We were also limited in correlating clinical and MRI outcomes as most of the CIS patients presented with minimal disability. However, one of the major strengths of our study is the largest sample size of CIS patients studied with a multimodal MRI approach, including DTI. When this study was designed, double inversion recovery (DIR) was not yet available on our scanner. The use of DIR could have helped to
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better estimate the amount and localization of GM lesion pathology, relevant for better association with the DTI outcomes [47,48]. In conclusion, we showed that diffuse FA abnormalities in whole brain and GM are detectable in CIS patients, when no significant changes can be observed in global, tissue specific or regional GM volumes. The lack of a relationship between lesion and DTI variables in the GM, as compared to a modest relationship with those in the WM, suggests that GM damage at the first clinical event may be to some extent, independent of lesion formation. Conflict of interest There is no conflict of interest. References [1] Frohman EM, Racke MK, Raine CS. Multiple sclerosis — the plaque and its pathogenesis. N Engl J Med 2006;354(9):942–55. [2] Polman CH, Reingold SC, Banwell B, Clanet M, Cohen JA, Filippi M, et al. Diagnostic criteria for multiple sclerosis: 2010 revisions to the McDonald criteria. Ann Neurol 2011;69(2):292–302. [3] Poloni G, Minagar A, Haacke EM, Zivadinov R. Recent developments in imaging of multiple sclerosis. Neurologist 2011;17(4):185–204. [4] Zivadinov R. Evidence for neuroprotection in multiple sclerosis: can imaging techniques measure neuroprotection and remyelination? Neurology 2007;68(3): S72–82. [5] Rocca MA, Cercignani M, Iannucci G, Comi G, Filippi M. Weekly diffusion-weighted imaging of normal-appearing white matter in MS. Neurology 2000;55(6):882–4. [6] Bozzali M, Cercignani M, Sormani MP, Comi G, Filippi M. Quantification of brain gray matter damage in different MS phenotypes by use of diffusion tensor MR imaging. AJNR Am J Neuroradiol 2002;23(6):985–8. [7] Barkhof F. The clinico-radiological paradox in multiple sclerosis revisited. Curr Opin Neurol 2002;15(3):239–45. [8] Rovaris M, Gass A, Bammer R, Hickman SJ, Ciccarelli O, Miller DH, et al. Diffusion MRI in multiple sclerosis. Neurology 2005;65(10):1526–32. [9] Rovaris M, Agosta F, Pagani E, Filippi M. Diffusion tensor MR imaging. Neuroimaging Clin N Am 2009;19(1):37–43. [10] Pagani E, Hirsch JG, Pouwels PJ, Horsfield MA, Perego E, Gass A, et al. Intercenter differences in diffusion tensor MRI acquisition. J Magn Reson Imaging 2010;31(6):1458–68. [11] Minagar A, Barnett MH, Benedict RH, Pelletier D, Pirko I, Sahraian MA, et al. The thalamus and multiple sclerosis: modern views on pathologic, imaging, and clinical aspects. Neurology 2013;80(2):210–9. [12] Fisniku LK, Altmann DR, Cercignani M, Tozer DJ, Chard DT, Jackson JS, et al. Magnetization transfer ratio abnormalities reflect clinically relevant grey matter damage in multiple sclerosis. Mult Scler 2009;15(6):668–77. [13] Calabrese M, Atzori M, Bernardi V, Morra A, Romualdi C, Rinaldi L, et al. Cortical atrophy is relevant in multiple sclerosis at clinical onset. J Neurol 2007;254(9):1212–20. [14] Henry RG, Shieh M, Amirbekian B, Chung S, Okuda DT, Pelletier D. Connecting white matter injury and thalamic atrophy in clinically isolated syndromes. J Neurol Sci 2009;282(1–2):61–6. [15] Ramasamy DP, Benedict RH, Cox JL, Fritz D, Abdelrahman N, Hussein S, et al. Extent of cerebellum, subcortical and cortical atrophy in patients with MS: a case–control study. J Neurol Sci 2009;282(1–2):47–54. [16] Henry RG, Shieh M, Okuda DT, Evangelista A, Gorno-Tempini ML, Pelletier D. Regional grey matter atrophy in clinically isolated syndromes at presentation. J Neurol Neurosurg Psychiatry 2008;79(11):1236–44. [17] Bergsland N, Horakova D, Dwyer MG, Dolezal O, Seidl ZK, Vaneckova M, et al. Subcortical and cortical gray matter atrophy in a large sample of patients with clinically isolated syndrome and early relapsing–remitting multiple sclerosis. AJNR Am J Neuroradiol 2012;33(8):1573–8. [18] De Stefano N, Matthews PM, Filippi M, Agosta F, De Luca M, Bartolozzi ML, et al. Evidence of early cortical atrophy in MS: relevance to white matter changes and disability. Neurology 2003;60(7):1157–62. [19] Raz E, Cercignani M, Sbardella E, Totaro P, Pozzilli C, Bozzali M, et al. Clinically isolated syndrome suggestive of multiple sclerosis: voxelwise regional investigation of white and gray matter. Radiology 2010;254(1):227–34. [20] Zivadinov R, Heininen-Brown M, Schirda CV, Poloni GU, Bergsland N, Magnano CR, et al. Abnormal subcortical deep-gray matter susceptibility-weighted imaging filtered phase measurements in patients with multiple sclerosis: a case–control study. Neuroimage 2012;59(1):331–9. [21] Behrens TE, Woolrich MW, Jenkinson M, Johansen-Berg H, Nunes RG, Clare S, et al. Characterization and propagation of uncertainty in diffusion-weighted MR imaging. Magn Reson Med 2003;50(5):1077–88. [22] Behrens TE, Johansen-Berg H, Woolrich MW, Smith SM, Wheeler-Kingshott CA, Boulby PA, et al. Non-invasive mapping of connections between human thalamus and cortex using diffusion imaging. Nat Neurosci 2003;6(7):750–7. [23] Benjamini Y, Hochberg Y. Controlling the false discovery rate — a practical and powerful approach to multiple testing. J R Stat Soc Ser B Methodol 1995;57(1):289–300.
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