Mirror Movements in Amyotrophic Lateral Sclerosis: A Combined Study Using Diffusion Tensor Imaging and Transcranial Magnetic Stimulation

A neurophysiological approach to mirror movements in amyotrophic lateral sclerosis

OBJECTIVE

To investigate mirror activity in amyotrophic lateral sclerosis (ALS) patients, using a simple paradigm of signal quantification.

METHODS

Patients were asked to perform a brief isometric maximum contraction of the abductor digiti minimi (ADM) or tibialis anterior (TA) on one side, while relaxing the contralateral side of the body. Both sides were investigated. Signals were stored and analyzed offline, for quantification of electromyographic signal. Clinical signs of upper motor neuron (UMN) dysfunction, transcranial magnetic stimulation (TMS) for the upper (UL) and lower limbs (LL), the ADM ipsilateral cortical silent period (iSP) and the Edinburgh Cognitive and Behavioral ALS Screen (ECAS) cognitive scale were also investigated.

RESULTS

42 ALS patients were included. In the 4 investigated muscles the amount of mirror activity was significantly higher than in the matched healthy group. The amount of mirror activity was similar between sides, but significantly higher in UL and LL with abnormal TMS results for ADM (p = 0.005) and TA (p = 0.002), as well as in UL with abnormal iSP values (p = 0.009). No association was found between mirror activity and clinical signs of UMN involvement.

CONCLUSIONS

Mirror activity is a common phenomenon in ALS. Mirror activity intensity corresponds to the severity of UMN dysfunction, as measured by TMS, and probably derives from the abnormal transcallosal inhibition as mirrored by iSP abnormality.

SIGNIFICANCE

Mirror activity is increased in ALS and is associated with abnormal transcallosal inhibition and UMN dysfunction.

Surface electromyography analysis of mirror movements under unilateral movement in stroke patients: A retrospective study

Objective

Mirror movements (MMs) are common abnormal motor performance in patients with poststroke hemiparesis. The study aimed to utilize the Electromyography (EMG) characterization of MMs in stroke patients and explore the relationship between MMs and the motor function of affected limbs.

Methods

Sixty patients with stroke who had used to undergo clinical assessment and surface Electromyography (sEMG) were selected in this study. We investigated the standardized net excitation (SNE) and overflow percentage (OF) as a measure of mirror activities on bilateral muscles of stroke patients.

Results

In stroke patients, mirror activities occurred in both affected and unaffected muscles during maximal contractions. We found that OF at unilateral contraction on the affected side (UCA) was significantly greater than that at unilateral contraction on the unaffected side (UCU). Additionally, a negative correlation between OF at UCA and Brunnstrom stages on admission and discharge. However, there were no significant correlations between OF and disease duration, Barthel Index, or the degree of improvement in all clinical evaluations. We still found a positive correlation between SNE at UCA and the improvement of the Brunnstrom stage of the hand. But we could not find any significant correlation between SNE and other clinical evaluation scores.

Conclusion

In conclusion, the study found mirror activities in both affected and unaffected muscles, confirming an asymmetry between them. Although the mechanisms are still unclear, we confirmed a significant correlation between MMs at UCA and the motor function of the affected upper extremity, which might provide further evidences for understanding MMs in stroke patients and a new research direction on evaluation for motor function and outcomes of stroke patients.

The ipsilateral silent period: an early diagnostic marker of callosal disconnection in ALS

Introduction:

Imaging studies showed affection of the corpus callosum (CC) in amyotrophic lateral sclerosis (ALS). Here, we sought to determine whether these structural alterations reflect on the functional level, using transcranial magnetic stimulation (TMS).

Methods:

In 31 ALS patients and 12 controls, we studied mirror movements (MM) and transcallosal inhibition (TI) using TMS. Structural integrity of transcallosal fibres was assessed using diffusion tensor imaging.

Results:

TI was pathologic in 25 patients (81%), 22 (71%) showed MM. Loss of TI was observed in very early stages (disease duration <4 months). No correlation was found between TI/MM and fractional anisotropy of transcallosal fibres.

Discussion:

These results substantiate the body of evidence towards a functional involvement of the CC in early ALS beyond microstructural alterations.

Significance:

TI may become a useful early diagnostic marker in ALS, even before descending tracts are affected. Diagnostic delay in ALS is high, often preventing patients from gaining access to therapeutic trials, and sensitive diagnostic tools are urgently needed. Our findings also provide insights into the pathophysiology of ALS, potentially supporting the so-called ‘top-down’ hypothesis, that is, corticoefferent (intracortical/corticospinal) propagation. Callosal affection in early stages might represent the ‘missing link’ to explain corticocortical disease-spreading.

Mirror Movements in Acquired Neurological Disorders: A Mini-Review

Mirror movements (MMs) are specifically defined as involuntary movements occurring on one side of homologous muscles when performing unilateral movements with the contralateral limb. MMs have been considered a kind of soft neurological signs, and the persistence or reappearance of MMs in adults is usually pathologic. In addition to some congenital syndrome, MMs have been also described in age-related neurological diseases including pyramidal system diseases (e.g., stroke, amyotrophic lateral sclerosis) and extrapyramidal disorders (e.g., Parkinson's disease, essential tremor). With the advances in instrumentation and detection means, subtle or subclinical MMs have been deeply studied. Furthermore, the underlying mechanism is also being further elucidated. In this mini-review, we firstly discuss the MM examination means, and then review the literature regarding MMs in individuals with acquired neurological disorders, in order to further understand the pathogenesis of MMs.

The cutaneous silent period in motor neuron disease

OBJECTIVE

To investigate the cutaneous silent period (CSP) by measuring its onset latency, duration and amount signal suppression in patients with motor neuron disease (MND) grouped according to the intensity of upper motor neuron involvement (UMN), and to test the effect of contralateral hand contraction.

METHODS

Painful stimulation was applied at the V finger, and contraction recorded from the abductor digiti minimi (ADM) muscle (baseline condition). Afterwards, CSP was studied during strong contralateral ADM contraction (test condition). 10-15 consecutive traces were recorded for each condition, signals were rectified, averaged, and analyzed offline.

RESULTS

46 patients were investigated, 15 with progressive muscular atrophy (PMA), 16 with typical amyotrophic lateral sclerosis (ALS), 15 with primary lateral sclerosis/predominant UMN-ALS (PLS+UMN-ALS), and 28 controls. In the baseline condition, all MND groups showed delayed onset latencies (p = 0.001). There was no significant difference in the CSP duration. Suppression was lower in the PLS + UMN-ALS group (p = 0.004). In the control group, contralateral contraction did not change CSP, but onset latency shortened significantly in the PMA group.

CONCLUSIONS

CSP onset latency is delayed in all investigated groups of MND, including in PMA, indicating subclinical UMN involvement. Changes in CSP can indicate UMN lesion in MND.

SIGNIFICANCE

CSP should be explored to identify UMN involvement in MND.

Pathophysiological associations of transcallosal dysfunction in ALS

AIM

Involvement of the corpus callosum has been identified as a feature of amyotrophic lateral sclerosis (ALS), particularly through neuropathological studies. The aim of the present study was to determine whether alteration in transcallosal function contributed to the development of ALS, disease progression and thereby functional disability.

METHODS

Transcallosal function and motor cortex excitability were assessed in 17 ALS patients with results compared to healthy controls. Transcallosal inhibition (interstimulus intervals (ISI) of 8-40 ms), short interval intracortical facilitation (SICF) and inhibition (SICI) were assessed in both cerebral hemispheres. Patients were staged utilising clinical and neurophysiological staging assessments.

RESULTS

In ALS, there was prominent reduction of transcallosal inhibition (TI) when recorded from the primary and secondary motor cortices compared to controls (F = 23.255, p < 0.001). This reduction of TI was accompanied by features indicative of cortical hyperexcitability, including reduction of SICI and increase in SICF. There was a significant correlation between the reduction in TI and the rate of disease progression (R = -0.825, p < 0.001) and reduction in muscle strength (R = 0.54, p = 0.031).

CONCLUSION

The present study has established that dysfunction of transcallosal circuits was an important pathophysiological mechanism in ALS, correlating with greater disability and a faster rate of disease progression. Therapies aimed at restoring the function of transcallosal circuits may be considered for therapeutic approaches in ALS.