Abnormal short-latency synaptic plasticity in the motor cortex of subjects with Becker muscular dystrophy: a rTMS study

Motor potential evoked by transcranial magnetic stimulation depends on the placement protocol of recording electrodes: a pilot study

OBJECTIVE

There seems to be no consensus in the literature regarding the protocol of surface electromyography (sEMG) electrode placement for recording motor evoked potentials (MEP) in transcranial magnetic stimulation (TMS) applications. Thus, the aim of this study was to investigate the effect on the MEP amplitude bytwo different protocols for electrode placement.

METHODS

sEMG electrodes were placed on three upper arm muscles (biceps brachii, flexor carpi radialis, and flexor pollicis brevis) of six right-handed subjects following two different protocols (1 and 2), which varied according to the interelectrode distance and location relative to the muscle. TMS pulses were applied to the hotspot of biceps brachii, while sEMGwas recorded from the two protocols and for each muscle simultaneously.

MAIN RESULTS

Greater MEP amplitudes were obtained for Protocol 1 compared to Protocol 2 (P < 0.05).

SIGNIFICANCE

Different electrode placement protocols may result in distinct MEP amplitudes, which should be taken into account when adjusting the intensity on single and repetitive TMS sessions.

Cortical involvement in myopathies: Insights from transcranial magnetic stimulation

OBJECTIVE

There is increasing evidence that an involvement of central nervous system (CNS) can occur in several myopathies. Transcranial magnetic stimulation (TMS) may represent a valuable tool for investigating important neurophysiological and pathophysiological aspects of cortical involvement in neuromuscular disorders. In this review paper we aimed to perform a systematic search of the studies employing TMS techniques in subjects suffering from myopathies.

METHODS

A literature search was conducted using PubMed and Embase. We identified and reviewed 9 articles matching the inclusion criteria. One hundred twenty patients were included in these studies, which have applied TMS in patients with muscle disorders.

RESULTS

To date, a few studies using TMS have been performed in myopathic patients and detected subclinical abnormalities in cortical reactivity and plasticity. The most consistent finding was a decrease in intracortical inhibition, which likely represents a non-specific compensatory mechanism of the CNS in an attempt to overcome the muscle deficit through an increase of the motor cortex output to deficient muscles.

CONCLUSIONS

Application of TMS to characterize the pathophysiology of the CNS in these subjects appears to be safe and may lead to the development of valuable biomarkers. Well-defined motor cortical excitability patterns can be identified in the different muscle diseases, even if preliminary findings should be confirmed in future studies in larger cohorts of patients.

SIGNIFICANCE

TMS studies may shed new light on the physiological and pathophysiological mechanisms underlying the cortical involvement in muscle disorders.

Toward a more personalized motor function rehabilitation in Myotonic dystrophy type 1: The role of neuroplasticity

Myotonic dystrophy type 1 (DM1) is the most prevalent adult muscular dystrophy, often accompanied by impairments in attention, memory, visuospatial and executive functions. Given that DM1 is a multi-system disorder, it requires a multi-disciplinary approach, including effective rehabilitation programs, focusing on the central nervous system neuroplasticity, in order to develop patient-tailored rehabilitative procedures for motor function recovery. Herein, we performed a transcranial magnetic stimulation (TMS) study aimed at investigating central motor conduction time, sensory-motor plasticity, and cortical excitability in 7 genetically defined DM1 patients. As compared to healthy individuals, DM1 patients showed a delayed central motor conduction time and an abnormal sensory-motor plasticity, with no alteration of cortical excitability. These findings may be useful to define patient-tailored motor rehabilitative programs.