Assessment of Motor Evoked Potentials in Multiple Sclerosis

Abstract

Transcranial magnetic stimulation (TMS) is a noninvasive technique mainly used for the assessment of corticospinal tract integrity and excitability of the primary motor cortices. Motor evoked potentials (MEPs) play a pivotal role in TMS studies. TMS clinical guidelines, concerning the use and interpretation of MEPs in diagnosing and monitoring corticospinal tract integrity in people with multiple sclerosis (pwMS), were established almost ten years ago and refer mainly to the use of TMS implementation; this comprises the magnetic stimulator connected to a standard EMG unit, with the positioning of the coil performed by using the external landmarks on the head. The aim of the present work was to conduct a narrative literature review on the MEP assessment and outcome measures in clinical and research settings, assessed by TMS Methodological characteristics of different TMS system implementations (TMS without navigation, line-navigated TMS and e-field-navigated TMS); these were discussed in the context of mapping the corticospinal tract integrity in MS. An MEP assessment of two case reports, by using an e-field-navigated TMS, was presented; the results of the correspondence between the e-field-navigated TMS with MRI, and the EDSS classifications were presented. Practical and technical guiding principles for the improvement of TMS studies in MEP assessment for MS are discussed, suggesting the use of e-field TMS assessment in the sense that it can improve the accuracy of corticospinal tract integrity testing by providing a more objective correspondence of the neurophysiological (e-field-navigated TMS) and clinical (Expanded Disability Status Scale—EDSS) classifications.

Characteristics of motor evoked potentials in patients with peripheral vascular disease

“…MEP characteristics have been exhaustively studied in heathy volunteers, and in specific spinal or neurological disease [10][11][12][13]. The MEPs of PVD patients, however, have not previously been examined.…”

The Cortical Silent Period in the Cricothyroid Muscle as a Neurophysiologic Feature for Dystonia Observation: E-Field-Navigated Transcranial Magnetic (TMS) Study

“…Previous TMS studies indicated a reduced inhibition as a characteristic of hand dystonia, cervical dystonia, and focal laryngeal dystonia (spasmodic dysphonia) [14]. To date, a cSP was reported only for TA muscles as a measure of LMC excitability in healthy subjects [11] and patients with laryngeal dystonia [14] using a line-navigated TMS system [15,16]. The cSP duration for TA muscles ranged from 41.7 ms to 66.4 ms in healthy subjects [11], and was found to be shortened in laryngeal dystonia subjects [14].…”

“…Moreover, the excitability of the LMC representation for CT muscles-as investigated by the cSP measure of the GABA receptor-mediated inhibition process-has not been previously evaluated. In the context of applying the TMS methodology in the research of the corticospinal tract and corticobulbar tract pathophysiology of disorders that affect the laryngeal muscles, the methodological use of e-field-navigated TMS is recommended over line-navigated TMS [6][7][8]15,16]. Line-navigated TMS is susceptible to errors because there is no visualization of a spot of maximal stimulation if there is a slight coil tilt.…”

Characteristics of motor evoked potentials in patients with peripheral vascular disease

“…MEP characteristics have been exhaustively studied in heathy volunteers, and in specific spinal or neurological disease. [10][11][12][13] The MEPs of PVD patients, however, have not previously been examined. Understanding changes that occur due to CLI is not only beneficial for IONM, but for any research or clinical situation where MEPs need to be characterised in patients with cardiovascular risk factors or recognised PVD.…”