Most studies concerning congenital mirror movements (CMMs) have been focused on the motor organization in the distal hand muscles exclusively. To the best of our knowledge, there is no data on motor organization pattern of lower extremities, and a scarcity of data on the significance of forearm and arm muscles in CMMs. Here, we describe the case of a 19-year-old boy presenting mirror movements. In these terms, a 10-year transcranial magnetic stimulation study demonstrated that the motor organization pattern of the arm muscles was different from that of distal hand and forearm muscles even in the same upper extremity, and that the lower extremities showed the same pathways as healthy children. Moreover, in this case, an ipsilateral motor evoked potentials (MEPs) for distal hand muscles increased in amplitude with age, even though the intensity of mirror movements decreased. In the arm muscles, however, it was concluded that the contralateral MEPs increased in amplitude with age.
To understand the motor control of the hand in patients with congenital mirror movements (CMMs), investigation of motor organization in distal hand muscles is important to develop viable interventions to improve patient outcomes. However, forearm and arm muscles also contribute to hand motor function and must be considered in these cases. Most studies concerning CMMs have been focused on the motor organization in the distal hand muscles only, and confirmed the dominance of the ipsilateral corticospinal pathways in those muscles. To the best of our knowledge, there is scarce data on forearm and arm muscles, and no data on the lower extremities in these cases [
In a previous study, we probed the ipsilateral corticospinal pathway in a patient with CMMs by examining neurophysiologic findings for the distal hand muscles [
The patient first visited our hospital at the age of 9, presenting with mirror movements [
His mirror movements were recently reassessed according to the Woods and Teuber scale [
Equally important, it is noted that the brain magnetic resonance imaging showed no abnormal findings. Similarly, the diffusion tensor images (DTI) were acquired using a Verio 3.0T system (Siemens, Erlangen, Germany) equipped with a 12-channel sensitivity encoding (SENSE) head coil for single-shot echo planar imaging. The imaging parameters utilized were: echo time=93 ms, repetition time=7,900 ms, field of view=230 mm×230 mm, sampling matrix size=128×128 reconstructed with homodyne processing to 256×256, SENSE factor=3, EPI=128, and bvalue=1,000 s/mm2. As a result, we acquired 47 contiguous, 3.0 mm thick slices parallel to the anterior commissure-posterior commissure line in 30 different diffusion directions. We therefore performed a tractography on the basis of fiber assignment by continuous tracking (FACT). The thresholds of the tracking termination were noted at 0.2 for the fractional anisotropy (FA) and 60° for the angle. Furthermore, for fiber tracking of the corticospinal tract (CST), two region of interest (ROI) were drawn on color-coded two-demensional FA map. For this purpose, a seed ROI was drawn at the CST portion in the anterior mid-pons and the target ROI in the anterior lower pons. As has been noted, the diffusion tensor tractography demonstrated normal symmetrical crossed CST (
In this study, we performed a TMS study spanning 10 years from aged 9 to 19. The possible physical and psychological complications from the study were explained to the patient, who gave written informed consent to participate in the study. The TMS system utilized was a MagPro (MagVenture, Lucernemarken, Denmark), and figure-8 type magnetic coils (70 mm in diameter) were used to stimulate the primary motor cortex. The recordings of ipsilateral motor evoked potentials (iMEPs) and contralateral motor evoked potentials (cMEPs) were made simultaneously at the bilateral first dorsal interosseous (FDI), extensor carpi radialis (ECR), biceps brachii (BB), deltoid, tibialis anterior, gastrocnemius and vastus medialis. Additionally, the FDI, ECR, and BB plus deltoid represent the distal hand, forearm, and arm muscles, respectively. In this case, the stimulation intensity was set at 110% of the resting motor threshold. It is noted that each hemisphere was stimulated four times, and the shortest latency and average peak to peak amplitudes were used for analysis.
In this case, iMEPs were evoked from all upper extremity muscles. At the FDI and ECR the amplitude and latency of iMEPs were noted as being higher and shorter than those of cMEPs (
The iMEPs in distal hand muscles increased in amplitude as the patient grew older, despite the decrement in intensity of the evaluated mirror movements. In the arm muscles, however, the cMEPs were seen to have increased in amplitude. Likewise, for forearm muscles, iMEPs were persistently dominant even though the iMEP/cMEP ratio was lower than for the distal hand muscles (
In this study, we performed whole exome sequencing to look for gene mutations that have been associated with CMMs, specifically
To begin with, the iMEPs of distal hand muscles became more dominant as the patient grew older. In the arm muscles, however, it is noted that the cMEPs increased in amplitude. In those cases, the iMEP/cMEP ratio was smaller in the forearm than in the distal hand, but the amplitudes of iMEPs were still larger than those of cMEPs. That being said, there was no evidence of an uncrossed corticospinal projection which was observed in the lower extremities.
In a previous TMS study of healthy children, we reported that cMEPs of distal hand muscles were noted and observed in infants. However, the cMEPs were not elicited in arm muscles, even in some children over 12 years of age. Moreover, the distal hand muscles showed a relevant amplitude increase at an earlier age than that of the arm muscles. This is a result of the late maturation of the CST projection to the proximal muscles [
In our earlier report, we concluded that the iMEPs of the distal hand in our patient did not reflect the existence of a branch of a crossed CST, but rather was shown to be more characteristic of an uncrossed CST [
The patient in this case had no other congenital deformity, unlike a patient we previously reported on with the characteristics of axial mesodermal dysplasia syndrome [
Our TMS study challenges the validity of the
No potential conflict of interest relevant to this article was reported.
Conceptualization: Park SH. Methodology: Kim ED, Kim GW, Won YH, Ko MH, Seo JH, Park SH. Formal analysis: Kim ED, Park SH. Funding acquisition: none. Project administration: Kim ED, Kim GW, Won YH, Ko MH, Seo JH, Park SH. Visualization: Kim ED, Park SH. Writing – original draft: Kim ED, Park SH. Writing – review and editing: Kim ED, Kim GW, Won YH, Ko MH, Seo JH, Park SH. Approval of final manuscript: all authors.
Axial color-coded fractional anisotropy map demonstrating well-defined blue color corticospinal tract (CST) at the level of the cerebral cortex (A) and pons (B). The normal connectivity of whole CST was confirmed by diffusion tensor tractography (C).
Trend of motor evoked potentials (MEPs) with age, generated by transcranial magnetic stimulation at left motor cortex (A) and right motor cortex (B). For the 1st dorsal interosseous and extensor carpi radialis, ipsilateral MEPs increased in amplitude as the patient grew older. In contrast, the contralateral MEPs increased in amplitude for the biceps brachii and deltoid.
Latencies of ipsilateral and contralateral MEPs in the upper extremities
Age (yr) | Left hemisphere |
Right hemisphere |
|||
---|---|---|---|---|---|
iMEP (ms) | cMEP (ms) | iMEP (ms) | cMEP (ms) | ||
FDI | 13 | 19.2±0.0 | 19.2±0.0 | 19.4±0.8 | 21.1±0.8 |
14 | 20.3±0.3 | 20.3±0.3 | 21.2±0.4 | 32.2±0.9 | |
15 | 20.1±0.1 | 20.4±0.3 | 22.1±0.3 | 28.8±0.1 | |
19 | 20.1±0.3 | 20.9±0.1 | 22.0±0.6 | 30.2±0.6 | |
ECR | 13 | 15.2±0.2 | 15.2±0.2 | 15.2±0.5 | 15.4±0.3 |
14 | 17.0±0.0 | 18.5±0.0 | 14.4±0.1 | 14.5±0.0 | |
15 | 16.2±0.2 | 19.2±0.6 | 16.0±0.1 | 21.2±0.7 | |
19 | 15.2±0.1 | 15.3±0.2 | 16.5±0.1 | 16.8±0.1 | |
BB | 13 | 13.1±0.4 | 14.0±0.5 | 14.5±0.4 | 13.1±0.1 |
14 | 16.4±0.2 | 15.0±0.0 | 16.0±0.4 | 12.7±0.2 | |
15 | 17.0±0.6 | 13.5±0.3 | 15.9±0.7 | 12.9±0.7 | |
19 | 15.6±0.1 | 12.8±0.6 | 16.1±0.2 | 14.1±0.2 | |
Del | 13 | 12.3±0.2 | 12.2±0.1 | 13.8±0.5 | 12.3±0.4 |
14 | 12.5±0.0 | 12.5±0.0 | 13.0±0.0 | 12.1±0.1 | |
15 | 15.3±0.6 | 14.4±0.8 | 15.0±0.7 | 12.6±0.4 | |
19 | 15.7±0.4 | 11.1±0.2 | 12.7±0.3 | 11.8±0.3 |
Values are presented as mean±standard deviation.
iMEP, ipsilateral motor evoked potential; cMEP, contralateral motor evoked potential; FDI, first dorsal interosseous; ECR, extensor carpi radialis; BB, biceps brachii; Del, deltoid.
iMEPs/cMEPs ratios and the frequency of ipsilateral MEPs of upper extremities
Age (yr) | Left hemisphere |
Right hemisphere |
|||
---|---|---|---|---|---|
iMEPs/cMEPs ratio | Freq. of iMEPs (%) | iMEPs/cMEPs ratio | Freq. of iMEPs (%) | ||
FDI | 13 | 5.0 | 100 | 6.3 | 100 |
14 | 4.4 | 100 | 9.0 | 100 | |
15 | 4.7 | 100 | 6.0 | 100 | |
19 | 3.7 | 100 | 10.8 | 100 | |
ECR | 13 | 1.4 | 100 | 2.7 | 100 |
14 | 1.2 | 100 | 1.9 | 100 | |
15 | 2.0 | 100 | 2.2 | 100 | |
19 | 1.4 | 100 | 2.2 | 100 | |
BB | 13 | 1.2 | 100 | 0.7 | 100 |
14 | 0.5 | 100 | 0.5 | 100 | |
15 | 0.9 | 100 | 0.2 | 100 | |
19 | 0.1 | 100 | 0.3 | 100 | |
Del | 13 | 0.6 | 100 | 0.5 | 100 |
14 | 0.8 | 100 | 0.3 | 100 | |
15 | 0.6 | 100 | 0.4 | 100 | |
19 | 0.6 | 100 | 0.4 | 100 |
MEPs, motor evoked potentials; iMEPs/cMEPs ratio, the ratio of amplitude of ipsilateral MEPs to contralateral MEPs; Freq. of iMEPs, the percentage of trials in which iMEPs are elicited by stimulation of the unilateral hemisphere; FDI, first dorsal interosseous; ECR, extensor carpi radialis; BB, biceps brachii; Del, deltoid.
Latency and amplitude of contralateral MEPs for the lower extremities
Age (yr) | Left hemisphere |
Right hemisphere |
|||||
---|---|---|---|---|---|---|---|
iMEP | cMEP |
iMEP | cMEP |
||||
Lat (ms) | Amp (μV) | Lat (ms) | Amp (μV) | ||||
TA | 13 | NE | 24.6±0.5 | 460.5±151.4 | NE | 25.2±0.4 | 395.2±45.5 |
14 | NE | 26.2±0.0 | 346.7±40.1 | NE | 27.0±0.0 | 190.5±16.2 | |
15 | NE | 27.3±0.2 | 253.6±31.9 | NE | 26.7±0.9 | 241.1±47.3 | |
19 | NE | 26.2±0.1 | 132.8±41.4 | NE | 26.9±0.1 | 265.0±45.1 | |
GCM | 13 | NE | 25.2±0.4 | 338.7±37.5 | NE | 25.0±0.0 | 315.2±72.7 |
14 | NE | 25.8±0.0 | 238.3±21.5 | NE | 26.8±0.0 | 156.3±26.6 | |
15 | NE | 26.9±0.5 | 454.4±48.0 | NE | 26.8±0.0 | 224.0±15.5 | |
19 | NE | 26.4±0.1 | 220.0±37.4 | NE | 26.9±0.1 | 245.0±28.9 | |
VM | 13 | NE | 20.4±0.5 | 532.2±128.0 | NE | 20.4±0.5 | 431.2±41.8 |
14 | NE | 24.0±0.0 | 328.7±39.6 | NE | 25.0±0.0 | 278.6±30.9 | |
15 | NE | 23.5±0.5 | 446.8±80.6 | NE | 24.5±0.4 | 422.1±21.9 | |
19 | NE | 22.9±0.1 | 147.5±40.3 | NE | 22.2±0.4 | 122.5±12.6 |
Values are presented as mean±standard deviation.
iMEP, ipsilateral motor evoked potential; cMEP, contralateral motor evoked potential; TA, tibialis anterior; GCM, gastrocnemius; VM, vastus medialis; NE, not evoked.