We aimed to investigate plastic changes in cerebral white matter structures using diffusion tensor imaging following a 15-day stroke rehabilitation program. We compared the detection of cerebral plasticity between generalized fractional anisotropy (GFA), a novel tool for investigating white matter structures, and fractional anisotropy (FA). Low-frequency repetitive transcranial magnetic stimulation (LF-rTMS) of 2400 pulses applied to the nonlesional hemisphere and 240 min intensive occupation therapy (OT) daily over 15 days. Motor function was evaluated using the Fugl-Meyer assessment (FMA) and Wolf Motor Function Test (WMFT). Patients underwent diffusion tensor magnetic resonance imaging (MRI) on admission and discharge, from which bilateral FA and GFA values in Brodmann area (BA) 4 and BA6 were calculated. Motor function improved following treatment (
Previously, we presented a novel therapeutic intervention for upper limb hemiparesis due to stroke consisting of combined treatment with low-frequency repetitive transcranial magnetic stimulation (rTMS) and intensive occupational therapy (OT) [
Numerous MRI studies have utilized generalized fractional anisotropy (GFA) values to obtain detailed information regarding brain structure [
To date, no clinical studies have utilized diffusion tensor MRI for the longitudinal investigation of changes in GFA values in patients undergoing rehabilitative intervention for the treatment of stroke-induced hemiparesis. Furthermore, the influence of repetitive transcranial magnetic stimulation (rTMS) on neural network development in the cerebral white matter has not been sufficiently studied in this patient population. Although not reported in our preliminary investigation, we observed no significant differences in FA values before and after our combined intervention (rTMS-OT therapy). While FA values can be used to represent diffusive anisotropy, these values decrease in regions of nerve fiber intersection, though no such reductions are observed for GFA values. Therefore, we performed diffusion tensor imaging to assess GFA values in patients with hemiparetic stroke both prior to and following combined rTMS-OT therapy.
A total of 36 patients who had experienced a stroke with upper limb hemiparesis were prospectively enrolled in the present study between March 19, 2011, and June 23, 2012. The inclusion criteria were as follows: (1) age between 18–80 years at intervention; (2) time after onset of stroke > 12 months; (3) history of a single symptomatic stroke only [no bilateral cerebrovascular lesion] and an intact cortex; (4) Brunnstrom recovery stage [
During hospitalization, patients underwent a 15-day combination treatment for their upper limb hemiparesis. Treatment consisted of twelve 40-minute low-frequency rTMS sessions combined with intensive OT, consisting of 120 min one-to-one training and 120 min self-training, which was provided following each rTMS. Both the treatment protocol and investigational approach for the present study were approved by the ethical committees of the Jikei University School of Medicine and Shimizu Hospital. Written informed consent was obtained from all patients prior to treatment.
The clinical characteristics of the patients are presented in Table
Patient characteristics.
Characteristic | Value |
---|---|
62.5 ± 10.2 | |
Female | 8 (22) |
Male | 28 (78) |
77.3 ± 50.3 | |
ICH | 18 (50) |
CI | 18 (50) |
Dominant hand | 20 (56) |
Nondominant hand | 16 (44) |
III | 4 (11) |
IV | 18 (50) |
V | 10 (28) |
VI | 4 (11) |
Values are presented as numbers (percentage) or means ± standard deviations. ICH: intracerebral hemorrhage; CI: cerebral infarction; BRS: Brunnstrom recovery stage.
Combined treatment with low-frequency rTMS and intensive OT was provided daily, except for Sundays. Using a 70 mm figure-8 coil attached to a MagPro R30 stimulator (MagVenture Company, Farum, Denmark), rTMS was delivered at a frequency of 1 Hz at the site of the nonlesioned hemisphere that elicited the largest motor-evoked potentials (MEPs) in the first dorsal interosseous (FDI) muscle of the unaffected upper limb. Each 40-minute low-frequency rTMS session consisted of 2400 pulses in total. The intensity of stimulation was set at 90% of resting motor threshold for the FDI muscle. For all patients, the laterality of the nonlesioned hemisphere was confirmed based on both physical evidence (the side of hemiparesis) and pretreatment MRI data.
OT was provided immediately after the application of low-frequency rTMS and consisted of both one-to-one training and self-training. The one-to-one training program was provided by an occupational therapist and consisted of shaping techniques (e.g., reaching forward to move a cup from one place to another, writing letters and pictures using a pencil) and repetitive task practice techniques (e.g., clay squeezing and molding, pinching small coins). Based on motor function of the affected upper limb and patient lifestyle (e.g., occupation, interests, and household work), the one-to-one training program was largely tailored at admission and sometimes modified during the course by the therapist to suit the individual needs of the patient.
Self-training tasks were similar to those applied in the one-to-one training. An occupational therapist evaluated patient performance on the training tasks after each self-training session and provided relevant feedback.
Motor function of the affected upper limb was evaluated using the Fugl-Meyer assessment (FMA) and Wolf Motor Function Test (WMFT) [
All patients underwent DTI using a 1.5 T magnetic field MRI system (ECHELON Vega, Hitachi Medico, Tokyo, Japan). The following imaging parameters were used: spin-echo diffusion echo planar image; number of axes: 21;
GFA is calculated from the following expression (
First, a T2-weighted image (T2WI) was extracted using IDL 6.4 (Exelis Visual Information Solutions, Boulder, CO). GFA scores were calculated by dividing the standard deviation by the root mean square (both derived from the apparent diffusion coefficient) and then visualized as a map. Images were then preprocessed using SPM8 (Wellcome Department, University College, London, UK) in MATLAB R2013a (Mathworks, Natick, MA). SPM8 is equipped with standard templates of the brain for T1WI and T2WI, but not with a standard brain map for GFA. Therefore, in the present study, we generated a standardized GFA map using the extracted T2WIs and their associated GFA maps. Smoothing was performed in SPM8 using a Gaussian filter. As noise increased following this standardization procedure, images were smoothed to improve signal-to-noise ratio. The full-width at half maximum (FMWH) was established at 6 mm. To prepare the mask images for our ROIs, we used the advanced mode in the MATLAB-compatible WFU-Pick Atlas toolbox [
Region-of-interest (ROI) models of Brodmann areas 4 and 6. Each color represents the ROIs encompassing the white matter of Brodmann areas 4, 6, and the corpus callosum, respectively.
Flowchart of analysis procedures.
All statistical analyses were performed using Statistical Package for Social Sciences, version 19.0 (SPSS, Chicago, IL). Changes in FMA for upper limb motor function were examined using the Wilcoxon signed-rank test. As we obtained a skewed distribution for WMFT performance times, we used the WMFT mean performance rate data. The data were analyzed using a new calculation, which consisted of calculating the rate of task performance (60/performance time). Subjects unable to complete a task within 120 seconds were assigned a rate of 0 [
Changes in the WMFT mean performance rate and WMFT-log performance time (WMFT-lpt) were examined using the Wilcoxon signed-rank test. WMFT-lpt was also used to analyze the effect of treatment on FA and GFA values for each of the two ROIs. Moreover, we performed correlation analyses of changes in GFA value for each ROI in both cerebral hemispheres in relation to the extent of motor function improvement. Changes in GFA value for each ROI and all correlations were assessed using the nonparametric Spearman’s rho. A
All patients completed the protocol without any adverse effects. The intervention resulted in significant improvements in motor function of the affected upper limb, as indicated FMA, WMFT. FMA scores increased from 45.4 ± 12.3 to 50.9 ± 12.0 points, while the WMFT mean performance rate increased from 24.1 ± 10.0 to 32.0 ± 13.8. In addition, WMFT-lpt decreased from 2.8 ± 1.2 to 2.4 ± 1.3 (Wilcoxon signed-rank test, all
As indicated in Table
Analysis of FA and GFA values.
Preintervention FA value (mean ± SD) | Postintervention FA value (range) | Preintervention GFA value (range) | Postintervention GFA value (range) | Correlation between GFA change and FMA change | Correlation between GFA change and WMFT-LPT change | |||||
---|---|---|---|---|---|---|---|---|---|---|
Lesioned hemisphere | 0.194 ± 0.023 | 0.195 ± 0.025 | 0.762 | 0.181 ± 0.006 | 0.186 ± 0.005 | 0.037 |
−0.137 | 0.420 | −0.363 | 0.030 |
Nonlesioned hemisphere | 0.207 ± 0.018 | 0.211 ± 0.013 | 0.069 | 0.193 ± 0.012 | 0.200 ± 0.014 | <0.001 |
−0.092 | 0.588 | −0.059 | 0.734 |
Lesioned hemisphere | 0.179 ± 0.006 | 0.181 ± 0.004 | 0.525 | 0.165 ± 0.0002 | 0.168 ± 0.001 | 0.093 | −0.155 | 0.359 | −0.236 | 0.165 |
Nonlesioned hemisphere | 0.189 ± 0.002 | 0.190 ± 0.003 | 0.822 | 0.172 ± 0.007 | 0.175 ± 0.005 | 0.054 | 0.042 | 0.804 | −0.269 | 0.112 |
Data are mean ± SD.
In the present study, we performed serial evaluation of GFA values in both the left and right hemispheres of patients treated with low-frequency rTMS and intensive OT over 15 days using a novel analytic technique based on diffusion MRI. To our knowledge, the present study is the first to investigate the influence of combined rehabilitative intervention using such methods. Our results indicate that the intervention not only improved upper limb hemiparesis but also changed the white matter structures directly under BA4 of the lesioned hemisphere, as well as under BA4 of the nonlesioned hemisphere. Furthermore, the extent of hemiparesis improvement was significantly correlated with increases in GFA value in the lesioned BA4, which suggests that recovery of motor function is at least partly due to structural changes in the cerebral white matter of the lesioned hemisphere.
FA is considered to reflect nerve fiber density, axial filament diameter, and myelination of white matter, and GFA values are similar to FA values in this respect. In addition, both FA and GFA values express the ease of movement of a water molecule in a range from 0 to 1. These values are calculated using DTI, such that a value of 0 indicates that movement of water molecules is relatively free and unaffected by a structural body (e.g., nerve fibers and medullary sheaths), whereas a higher value indicates a strong directionality imparted by the structural body on the motion of water molecules. GFA values are high for white matter due to the density of the nerve fibers, slightly lower for gray matter, and close to 0 for cerebrospinal fluid. Further research suggests that DTI is useful for the evaluation of cerebral white matter nerve fibers in patients who have experienced cerebrovascular accidents [
In this way, GFA could reflect the state of diffusing water molecules in greater detail than FA. That is, more information about each direction of diffusion can be obtained from the GFA calculation as compared to the FA calculation, which is calculated using eigenvalues of
The two ROIs in the present study were chosen due to their association with functions related to voluntary movement. Namely, BA4 (the primary motor cortex) and BA6 (composed of the premotor cortex and the supplementary motor area) are associated with voluntary movement, and these areas receive inputs from BA5 and BA7, which unify information from the somatosensory optic areas. While these BAs consist of both gray and white matter, the ROIs targeted only the white matter structures. Gray matter was not included in the analysis, as the presence of many dendrites inhibits observed changes in FA or GFA. Some research has indicated that poststroke movement disorders occur due to injury to regions associated with voluntary movement [
Changes in GFA value for BA4 (lesioned side) exhibited an inverse correlation with changes in WMFT-lpt. Using fMRI, our group previously observed that cerebral cortical activation localizes significantly to the lesioned cerebral hemisphere in patients undergoing rTMS-OT intervention [
Researchers have long acknowledged that plastic changes in the central nervous system are associated with the formation of new neural networks in stroke recovery [
We further attempted to examine correlational changes in the cortex and white matter and to speculate on the mechanisms underlying changes in GFA values. Diffusion of water molecules is limited by white matter structures associated with nerve fibers, primarily the medullary sheath. Thus, increases in GFA values may be due to axonal sprouting or myelination, whereas decreases may be the result of axonal degeneration. It is worth noting that, while FA values decrease at the intersection of fibers, GFA values remain unaffected. Therefore, we can infer that tissue degeneration—rather than the presence of fiber intersections—is responsible for decreases in GFA value. Furthermore, white matter degeneration is thought to be associated with functioning of nearby gray matter, as the nerve fibers convey signals from the cell’s perikaryon. Therefore, we maintain that the decrease in GFA values may be directly related to white matter denaturation and plastic changes associated with regaining cortical function.
The present study has certain limitations. First, the study included only 36 patients and lacked a control group. The lack of a control group or condition, however, is mitigated by our previous study that included controls and replicated clinical findings over multiple sites [
Accordingly, the observed clinical improvements could be due to specific effects. In addition, the white matter changes might happen. Another factor that makes the lack of a control group a lesser limitation than otherwise is that the participants had experienced stroke > 1 year previously, and thus they were long past the time window during which spontaneous recovery takes place. Second, previous reports have used GFA on high-angular-resolution-diffusion imaging data with 200+ directions [
The application of low-frequency rTMS combined with intensive OT resulted in increased GFA values in BA4, as well as improvements in upper limb hemiparesis, suggesting that the combined rTMS-OT intervention may induce beneficial plastic changes in cerebral white matter structures, though the lack of a control group in the present study limits this interpretation. Serial assessments of GFA values seem to provide reliable evidence of structural changes in cerebral white matter in patients undergoing rehabilitative intervention following hemiparetic stroke, although further studies are required to verify this finding.
The abstract was published in
All authors declare they have no conflicts of interest to disclose.
The authors gratefully acknowledge the participation of the patients in the study, and Hidenobu Saeki, RPT; Junichi Nishimura, OTR; Chika Kodani, for collecting and evaluating motor function data. Funding for this study was provided by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.