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Research Article

A pilot study of basal ganglia and thalamus structure by high dimensional mapping in children with Tourette syndrome

[version 1; peer review: 2 approved]
PUBLISHED 08 Oct 2013
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This article is included in the Rare diseases collection.

This article is included in the Tics collection.

Abstract

Background: Prior brain imaging and autopsy studies have suggested that structural abnormalities of the basal ganglia (BG) nuclei may be present in Tourette Syndrome (TS). These studies have focused mainly on the volume differences of the BG structures and not their anatomical shapes.  Shape differences of various brain structures have been demonstrated in other neuropsychiatric disorders using large-deformation, high dimensional brain mapping (HDBM-LD).  A previous study of a small sample of adult TS patients demonstrated the validity of the method, but did not find significant differences compared to controls. Since TS usually begins in childhood and adult studies may show structure differences due to adaptations, we hypothesized that differences in BG and thalamus structure geometry and volume due to etiological changes in TS might be better characterized in children.
Objective: Pilot the HDBM-LD method in children and estimate effect sizes.
Methods: In this pilot study, T1-weighted MRIs were collected in 13 children with TS and 16 healthy, tic-free, control children. The groups were well matched for age.  The primary outcome measures were the first 10 eigenvectors which are derived using HDBM-LD methods and represent the majority of the geometric shape of each structure, and the volumes of each structure adjusted for whole brain volume. We also compared hemispheric right/left asymmetry and estimated effect sizes for both volume and shape differences between groups.
Results: We found no statistically significant differences between the TS subjects and controls in volume, shape, or right/left asymmetry.  Effect sizes were greater for shape analysis than for volume.
Conclusion: This study represents one of the first efforts to study the shape as opposed to the volume of the BG in TS, but power was limited by sample size. Shape analysis by the HDBM-LD method may prove more sensitive to group differences.

Introduction

Tourette syndrome (TS) is a chronic idiopathic syndrome characterized by the appearance of both vocal and motor tics during childhood or adolescence1,2. Tics are repetitive, stereotyped, suppressible movements or vocalizations that may include blinking, abdominal tensing, sniffing, or throat clearing3. TS affects approximately 0.5% of school-age children, but its causes and pathophysiology are not yet well understood4.

It has been suggested that problems with activity modulation in the basal ganglia and thalamus may contribute to the inability of TS patients to exercise behavioral inhibition5,6 as a result of these structures’ effects on behavioral inhibition via the prefrontal, parietal, temporal, and cingulate cortices7. The basal ganglia and thalamus modulate cortical activity through cortico-basal ganglia-thalamo-cortical loops, composed of connections from the frontal cortex to the striatum, the striatum to the globus pallidus, substantia nigra, and thalamus, and the thalamus back to the cortex8.

Several lines of evidence support the presence of structural abnormalities in basal ganglia nuclei in individuals with TS4. Autopsy studies have found abnormalities within the basal ganglia, including increased number of neurons in the globus pallidus interna, decreased density and number of neurons in the globus pallidus pars externa, and decreased parvalbumin and choline acetyltransferase staining cholinergic interneurons in the caudate nucleus and putamen9,10. However, since TS is rarely a fatal disease, the number of autopsied cases is limited11. Case studies of focal brain lesions have demonstrated new tic onset after lesions to the prefrontal cortex, thalamus, and basal ganglia12. In addition, encephalitis lethargica, frontal lobe degeneration, Huntington disease, Wilson disease, and other degenerative illnesses are associated with tics12. Further, some TS patients have benefitted from deep brain stimulation of the globus pallidus and thalamus in TS1316. Collectively, these observations suggest a role for the basal ganglia, thalamus, and frontal cortex in tics.

Neuroimaging studies can be especially beneficial for studying structural abnormalities because they allow longitudinal study design, reduced investigator and sampling bias, and are relatively non-invasive. A number of MRI studies have examined anatomical volumes and cortical thickness in children and adults with TS and reported significant differences in various brain regions, including the caudate, sensorimotor and prefrontal cortex, and corpus callosum17. Most consistently, basal ganglia volumes were found to be smaller in TS subjects compared with healthy controls, but neuroanatomical shape differences and asymmetry abnormalities have not yet been consistently described1824.

Large-deformation high dimensional brain mapping (HDBM-LD) is a computational anatomy tool that reduces the potential for human error in image analysis by further automating elements of image analysis. It has been successfully employed in characterizing shape and volume abnormalities of the hippocampus in neuropsychiatric disorders such as schizophrenia2527, dementia of the Alzheimer type2831, depression32 and epilepsy33. It has also been applied to examine the thalamus in schizophrenia34.

HDBM-LD was applied to assess volume and shape differences in putamen, caudate nucleus, nucleus accumbens, globus pallidus, and thalamus in 15 adults with TS and 15 matched controls. No differences in volume or shape were found35. However, TS begins before adulthood. Several structural imaging studies in TS have found an interaction between regional brain volumes and age21,22. It has been suggested that differences seen in adult studies may reflect adaptations or selection bias rather than changes etiologically relevant to TS20. Thus the present study applied HDBM-LD to investigate the volume and shape of these structures in children. We hypothesized that we would find reduced volume, abnormal shape, or abnormal right-to-left asymmetry in one or more of these structures, compared to age-matched controls. Given that there were no prior studies using the HDBM-LD method to analyze brain structures of children with TS in the literature, another goal of this pilot study was to estimate the effect size of these measures in this population.

Materials and methods

Ethics statement

A parent of each subject gave written informed consent to participate in the study, and each subject assented to participation. The study was approved by the Washington University Human Studies Committee (approval # 03-1282).

Participants

This study included 13 children with TS (mean age (SD) = 12.44 (2.22), 3 female, 12 right-handed) and 16 healthy controls (mean age (SD) = 12.39 (1.92), 2 female, 15 right-handed). A movement disorders-trained physician examined all TS subjects and 10 of the control subjects. The remaining control subjects underwent neuropsychological evaluation as described previously36. Exclusion criteria were: inability to give informed consent, contraindication to MRI, currently symptomatic major depression, or lifetime history of mental retardation, autism, psychosis, mania, anorexia, bulimia, or drug abuse. All TS subjects met DSM-IV-TR criteria either for Tourette’s Disorder or Chronic Tic Disorder. Disease duration and severity and other clinical characteristics are summarized in Table 1.

Table 1. Subject characteristics.

TS groupControl group
n 1316
Age at scan (mean ± sd)12.44 ± 2.2212.39 ± 1.92
Sex3F/10M2F/14M
Handedness12R/1A15R/1L
Years since onset of tics ± sd4.31 ± 2.69NA
YGTSS total tic score* ± sd19.00 ± 11.66NA
Number with ADHD diagnosis40
Number with OCD diagnosis50
Number who reported currently taking medication:
Atypical neuroleptics10
Typical neuroleptics10
Stimulants10
Benzodiazepines00
Selective serotonin reuptake inhibitors30
alpha-2 agonists50
Tricyclic antidepressants20
Tetracyclic antidepressants10
1st generation antihistamines20
Number who reported past use of medication:
Atypical neuroleptics10
Typical neuroleptics10
Stimulants30
Benzodiazepines10
Selective serotonin reuptake inhibitors10
alpha-2 agonists50
Tricyclic antidepressants00
Tetracyclic antidepressants00

*YGTSS total tic score includes only the motor tic and vocal tic subscores for a maximum of 50 points. R = right-handed, L = left-handed, A = ambidextrous.

Image acquisition and preprocessing

A 1.5 T Siemens Vision system with a standard head receiver coil was used to collect T1-weighted MR structural images. Prior to scanning sessions, the transmitter was tuned and the main field was shimmed. Anatomic images used a 3D T1-weighted sequences (MPRAGE, 1x1x1.25 mm3 voxels)37. Individual MPRAGE collections lasted approximately 6.5 minutes.

Initial image processing was done as described previously35,38. Using AnalyzeTM software (Rochester, Minnesota), images were linearly rescaled so that voxels with intensity two standard deviations above the mean in the corpus callosum were mapped to 255, and voxels with intensity levels two standard deviations below the mean in the lateral ventricles were mapped to 0.

Whole-brain volume for each subject, excluding the ventricles, was obtained from FreeSurfer (http://surfer.nmr.mgh.harvard.edu/)39.

Large-Deformation High-Dimensional Brain Mapping (HDBM-LD)

HDBM-LD was used to determine the volume and shape of the brain structures of interest in all subject scans, as described in detail elsewhere35. Briefly, on each subject’s brain image, a single rater (MEMcN) marked 27 points on the boundaries of the basal ganglia and thalamus in each hemisphere, which were used as an initial step to roughly align the brain image to a labeled standard brain image (template). From this starting point a differentiable, invertible transformation was computed that mapped all voxels of the subject’s image to the template. Using this transformation, the labels on the template image are automatically assigned to the corresponding voxels of each subject’s image. The authors checked the segmentation of each subject’s MR image by visual inspection. This method is extremely reliable and has been validated against expert manual tracings35.

Brain structure volume and shape analysis

All brain structure volume and shape analysis methods were conducted as described previously35. We examined five structures: caudate nucleus, nucleus accumbens, globus pallidus, putamen, and thalamus. Volume for each structure was analyzed using a repeated measures ANCOVA, with diagnostic group as the between-subjects factor, brain hemisphere as the within-subjects factor, and age and whole brain volume as covariates. The degree of volumetric asymmetry was examined with the hemisphere effect, and group differences in volumetric asymmetry were assessed by examining the group-by-hemisphere interactions. We also analyzed the total (left and right hemisphere) structure volumes using an ANCOVA. The volume ANCOVAs were repeated with other covariates and factors, including estimated total intracranial volume, sex and handedness, none of which substantively changed the results.

Brain structure shapes were determined from the inter-subject deformation vector fields provided by the HDBM-LD transformations. Eigenvalues and a complete orthonormal set of eigenvectors representing shape variation were obtained using singular value decomposition (SVD) of the pooled covariance in the population studied. The coefficients (eigenscores) associated with the eigenvalues and eigenvectors were calculated for each subject and for each structure in each hemisphere35,40. We used the eigenscores based on the first ten eigenvectors for each structure in each hemisphere in a multivariate ANCOVA to test for group differences in shape. These first ten eigenscores explained 81–92% of the total variance for each structure.

Results

Volume

Repeated-measures ANCOVAs showed no significant group effect for any structure. Structural volumes and ANCOVA statistics are shown in Table 2. Additionally, no significant hemisphere effects or group by hemisphere interactions were seen for any of the five structures examined (see Table 2).

Table 2. Volumes of the structures of interest (mm3).

TS (n = 13)Control (n = 16)ANCOVA statistics (hemisphere by dx)
Mean (std)[95% CIs] mm3 Mean (std)[95% CIs] mm3 F df P
CaudateL
R
T
3736 (271)
3712 (545)
7448 (731)
[3581, 3890]
[3401, 4023]
[7030, 7865]
3667 (270)
3678 (543)
7345 (729)
[3528, 3806]
[3398, 3957]
[6969, 7720]

0.040

1,25

0.84
Nucleus accumbensL
R
T
460 (46)
455 (50)
915 (74)
[434, 487]
[426, 483]
[873, 957]
462 (46)
456 (50)
918 (73)
[438, 485]
[430, 481]
[880, 955]

0.000

1,25

0.996
Globus pallidusL
R
T
1826 (126)
1859 (145)
3685 (248)
[1754, 1898]
[1776, 1942]
[3544, 3827]
1804 (125)
1800 (144)
3603 (247)
[1739, 1868]
[1726, 1874]
[3476, 3730]

0.768

1,25

0.39
PutamenL
R
T
5925 (367)
5822 (401)
11748 (724)
[5716, 6135]
[5593, 6052]
[11334, 12161]
5705 (365)
5671 (399)
11376 (721)
[5517, 5893]
[5465, 5877]
[11005, 11748]

0.487

1,25

0.49
ThalamusL
R
T
8076 (557)
8143 (480)
16219 (805)
[7757, 8394]
[7869, 8418]
[15759, 16679]
7931(555)
7888 (478)
15819 (802)
[7645, 8217]
[7642, 8134]
[15406, 16232]

0.196

1,25

0.66

L = left, R = right, T = total volume. Repeated-measures ANOVA of each structure showed no significant group effect. Further, we found no hemisphere effect or group by hemisphere interactions for any of the structures (age and whole brain volume w/out ventricles as covariates).

Shape

MANCOVAs (using the first ten eigenscores as dependent variables) for each structure in each hemisphere showed no significant group effect (see Table 3). Effect sizes (Cohen’s ƒ2) for both volume and shape are provided in Table 4; the effect sizes for the shape comparisons were larger than those for the volume comparisons.

Table 3. Shape comparison of the thalamus and basal ganglia structures (TS vs. control).

MANCOVA statistics
StructureF df P
Nucleus accumbensL
R
1.63
1.91
10,17
10,17
0.18
0.11
CaudateL
R
1.31
.739
10,17
10,17
0.30
0.68
Globus pallidusL
R
.231
.848
10,17
10,17
0.99
0.59
PutamenL
R
.285
.740
10,17
10,17
0.98
0.68
ThalamusL
R
.705
.893
10,17
10,17
0.71
0.56

L = left, R = right, T = total volume. Multivariate analysis of the first 10 eigenvectors of each structure showed no significant group effect (age as covariate).

Table 4. Effect sizes.

Partial ηCohen’s ƒ2
Volumes (total structure volumes)
Caudate5.51 × 10-3 5.54 × 10-3
Nucleus accumbens2.77 × 10-4 2.78 × 10-4
Globus pallidus2.94 × 10-2 3.03 × 10-2
Putamen6.79 × 10-2 7.29 × 10-2
Thalamus6.42 × 10-2 6.86 × 10-2
Volumes (hemisphere * dx effects)
Caudate2.00 × 10-3 2.00 × 10-3
Nucleus accumbens1.22 × 10-6 1.22 × 10-6
Globus pallidus3.00 × 10-2 3.09 × 10-2
Putamen1.90 × 10-2 1.94 × 10-2
Thalamus8.00 × 10-3 8.06 × 10-3
Shapes (principal components):
Left
Caudate0.4360.773
Nucleus accumbens0.4900.961
Globus pallidus0.1200.136
Putamen0.1440.168
Thalamus0.2930.414
Right
Caudate0.3030.435
Nucleus accumbens0.5301.128
Globus pallidus0.3330.499
Putamen0.3030.435
Thalamus0.3440.524

Discussion

Using HDBM-LD, a validated method for automatic, high-dimensional mapping of basal ganglia and thalamic structures, we found no significant differences in basal ganglia volumes or shape between children with TS and matched control children. For most basal ganglia regions, this reflects the conclusions of a recent review17. For instance, two groups found increased putamen volume in TS41,42, but a larger study found decreased volume43. However, the majority of these studies found no abnormality in putamen, similar to the current study. Three other studies, including the HDBM-LD study in adults with TS, found no volumetric change in any basal ganglia structure35,4446. Possibly there is no true difference in these structures in TS when groups are matched carefully for age, sex and handedness. Alternatively, structural abnormalities in TS may be limited to certain subgroups, such as those with more severe tics or with ADHD.

On the other hand, the largest published MRI study of basal ganglia volume compared 154 adults and children with TS to 130 tic-free control subjects, and found that the caudate was 4.9% smaller in the TS group (p<0.01)43. Two other groups also found lower caudate volume in samples of 18–23 TS subjects and a similar number of controls23,24,47,48. The possible etiologic relevance of this finding is highlighted by the observation that a smaller caudate nucleus in adolescents with TS predicts more severe symptoms in early adulthood49. The largest of the studies that did not find significant decreases in caudate volume was that of Roessner et al.42, which compared 55 subjects with TS to 42 control subjects. The other studies with negative findings regarding caudate volume, including the present one, had fewer than 20 TS subjects each. It is possible these negative results represent a Type II error.

The present study and the HDBM-LD study in adults represent some of the first efforts to study the shape (as opposed to the volume) of basal ganglia nuclei in TS, and provide effect size estimates for planning a study with larger samples.

Comments on this article Comments (1)

Version 1
VERSION 1 PUBLISHED 08 Oct 2013
  • Author Response (F1000Research Advisory Board Member) 14 Oct 2015
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    14 Oct 2015
    Author Response F1000Research Advisory Board Member
    Garraux et al 2006 (doi:10.1002/ana.20765) can be added to the list of studies of brain structure in TS that did not find a significantly smaller caudate nucleus.
    Competing Interests: No competing interests were disclosed.
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Williams AC, McNeely ME, Greene DJ et al. A pilot study of basal ganglia and thalamus structure by high dimensional mapping in children with Tourette syndrome [version 1; peer review: 2 approved]. F1000Research 2013, 2:207 (https://doi.org/10.12688/f1000research.2-207.v1)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 1
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PUBLISHED 08 Oct 2013
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Reviewer Report 27 Mar 2014
Kirsten R Müller-Vahl, Clinic of Psychiatry, Social psychiatry and Psychotherapy, Hannover Medical School, Hannover, Germany 
Approved
VIEWS 28
In this study a relatively new and sophisticated method (using large-deformation, high dimensional brain mapping (HDBM-LD)) has been used to investigate for the first time structure geometry and volume of basal ganglia and thalamus in 13 children with Tourette syndrome ... Continue reading
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Müller-Vahl KR. Reviewer Report For: A pilot study of basal ganglia and thalamus structure by high dimensional mapping in children with Tourette syndrome [version 1; peer review: 2 approved]. F1000Research 2013, 2:207 (https://doi.org/10.5256/f1000research.2550.r4285)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 27 Mar 2014
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    27 Mar 2014
    Author Response
    We appreciate Dr. Müller-Vahl's thoughtful comments.
    Competing Interests: No competing interests were disclosed.
COMMENTS ON THIS REPORT
  • Author Response 27 Mar 2014
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    27 Mar 2014
    Author Response
    We appreciate Dr. Müller-Vahl's thoughtful comments.
    Competing Interests: No competing interests were disclosed.
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Reviewer Report 24 Jan 2014
Jeremy S. Stern, Department of Neurology, St. George's Hospital and Medical School, London, UK 
Approved
VIEWS 33
This study continues the quest for subtle structural abnormalities in striato-thalamo-cortical circuitry in Tourette syndrome. The technique is innovative and in this paper is negative for a relatively small number of children as it has been for a similar number ... Continue reading
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HOW TO CITE THIS REPORT
Stern JS. Reviewer Report For: A pilot study of basal ganglia and thalamus structure by high dimensional mapping in children with Tourette syndrome [version 1; peer review: 2 approved]. F1000Research 2013, 2:207 (https://doi.org/10.5256/f1000research.2550.r3072)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 11 Feb 2014
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    11 Feb 2014
    Author Response
    We greatly appreciate Prof. Stern's thoughtful comments about the relevance and limitations of this pilot study. The prior report (ref. 35 above) does describe the methods in detail.
    Competing Interests: No competing interests were disclosed.
COMMENTS ON THIS REPORT
  • Author Response 11 Feb 2014
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    11 Feb 2014
    Author Response
    We greatly appreciate Prof. Stern's thoughtful comments about the relevance and limitations of this pilot study. The prior report (ref. 35 above) does describe the methods in detail.
    Competing Interests: No competing interests were disclosed.

Comments on this article Comments (1)

Version 1
VERSION 1 PUBLISHED 08 Oct 2013
  • Author Response (F1000Research Advisory Board Member) 14 Oct 2015
    Kevin J Black, Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
    14 Oct 2015
    Author Response F1000Research Advisory Board Member
    Garraux et al 2006 (doi:10.1002/ana.20765) can be added to the list of studies of brain structure in TS that did not find a significantly smaller caudate nucleus.
    Competing Interests: No competing interests were disclosed.
Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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