Frequency-dependent conduction delay of motor-evoked potentials in multiple sclerosis

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Quantitative Ultrasound Imaging to Assess Skeletal Muscles in Adults with Multiple Sclerosis: A Feasibility Study

OBJECTIVES

The aim of this study was to assess the feasibility of quantitative ultrasound imaging (QUI) in assessing the biceps brachii muscle and gastrocnemius muscle in adults with multiple sclerosis (MS).

METHODS

From May to October 2018, we prospectively performed B-mode ultrasound imaging and ultrasound strain elastography of the biceps brachii muscle and gastrocnemius muscle in 24 patients with MS and 10 age-matched healthy volunteers. ImageJ (https://imagej.nih.gov/ij) was used to assess the muscle pixel intensity in grayscale images. Using 2-dimensional speckle-tracking software, we estimated the muscle axial peak strain (maximum deformation) produced by manual compression with an ultrasound transducer and the muscle longitudinal peak strain (maximum displacement) produced by passive elbow and ankle movements. Muscle QUI parameters used in the study included the mean pixel intensity, axial peak strain ratio (SR = muscle strain/subcutaneous tissue strain), and longitudinal peak SR. Statistical analyses included 1-way analysis of variance and a post hoc test to examine the differences in QUI parameters among 3 groups (1, affected muscle in patients with MS; 2, unaffected muscle in patients with MS; and 3, healthy muscle in controls) and, in all paired groups, an unpaired t test to compare the muscle SR in patients with MS with a Modified Ashworth Scale (MAS) score of 1 or higher to those with an MAS score of 0.

RESULTS

The mean age of the 24 patients with MS was 43 years, and all patients and volunteers were female. We observed a significant difference in QUI parameters among the affected muscle in MS, unaffected muscle in MS, and healthy muscle in all paired groups and in patients with MS between an MAS score of 1 or higher and an MAS score of 0 (all P < .05). Interobserver and intraobserver variability in performing QUI was good (intraclass correlation coefficients >0.75).

CONCLUSIONS

Our results suggest that QUI is feasible to assess muscle echogenicity and mechanical behaviors in adult MS.

A qualitative review of the neurophysiological underpinnings of fatigue in multiple sclerosis

Fatigue is debilitating in multiple sclerosis (MS) and may have multiple causes. Recent investigations into objectively measurable correlates of fatigue have used transcranial magnetic stimulation (TMS) to examine a range of neurophysiological measures of neural excitability that may be altered in patients with MS. This qualitative review was conducted to test the hypothesis that changes in neural excitability are a contributing factor in MS-related fatigue. A search of the English language literature led to the compilation and synthesis of original research papers in which various aspects of neural excitability and neural transmission were measured using TMS in patients with MS. The resulting papers were classified into three categories of study relevant to fatigue: abnormalities in excitability and their correlation with self-reported fatigue; effects of exercise-induced fatigue on neural excitability; and effects of fatigue medications on neural excitability. Evidence of an association between fatigue and intracortical inhibition is both limited and conflicting, and no evidence suggests associations of fatigue with corticomotor excitability or neuronal conduction. Pharmacologically-induced changes in fatigue were found to correlate with changes in intracortical excitability. No conclusions could be drawn regarding neural excitability and exercise-induced fatigue, due to variability in study populations, outcome measures, and exercise protocols across different studies. Suggestions for future studies in this area are proposed with a view to identifying potentially modifiable factors contributing to fatigue in MS.

Effects of long-term resistance training and simultaneous electro-stimulation on muscle strength and functional mobility in multiple sclerosis

Background: Resistance training studies in multiple sclerosis (MS) often use short intervention periods. Furthermore, training efficiency could be optimized by unilateral training and/or electrical stimulation.

Objective: To examine the effect(s) of unilateral long-term (20 weeks) standardized resistance training with and without simultaneous electro-stimulation on leg muscle strength and overall functional mobility.

Methods: A randomized controlled trial involving 36 persons with MS. At baseline (PRE) and after 10 (MID) and 20 (POST) weeks of standardized (ACSM) light to moderately intense unilateral leg resistance training (RESO, n = 11) only or resistance training with simultaneous electro-stimulation (RESE, n = 11, 100 Hz, biphasic symmetrical wave, 400 µs), maximal isometric strength of the knee extensors and flexors (45°, 90° knee angle) and dynamic (60–180°/s) knee-extensor strength was measured and compared with a control group (CON, n = 14). Functional mobility was evaluated using the Timed Get Up and Go, Timed 25 Foot Walk, Two-Minute Walk Test, Functional Reach and Rivermead Mobility Index.

Results: Maximal isometric knee extensor (90°, MID: +10 ± 3%, POST: +10 ± 4%) in RESO and knee flexor (45°, POST: +7 ± 4%; 90°, POST: +9 ± 5%) in RESE strength increased ( p < 0.05) compared with CON but RESO and RESE did not differ. Also, impaired legs responded positively to resistance training (unilateral leg strength analysis) and functional reaching increased significantly in RESO (+18%) compared with CON. Dynamic muscle strength and the remaining functional mobility tests did not change.

Conclusion: Long-term light to moderately intense resistance training improves muscle strength in persons with MS but simultaneous electro-stimulation does not further improve training outcome.

Prolonged intracortical delay of long-latency reflexes: electrophysiological evidence for a cortical dysfunction in multiple sclerosis

Convincing evidence suggests that long-latency reflexes (LLRs) are capable of testing the transcortical sensorimotor reflex arch. By subtracting the sum of the latencies of N20 (afferent branch) and transcranially elicited motor evoked potentials (MEP; efferent branch) from the LLR II latency, the cortical relay time (CRT) can also be obtained, which is alleged to represent the time required for the cortical sensorimotor integration. The aim of the present study was to investigate if a cortical dysfunction occurs in multiple sclerosis (MS). Median nerve somatosensory evoked potentials (SEPs), MEPs and LLRs were recorded from the upper limbs of 23, not severely disabled MS patients in acute phases of the disease. Eighteen age and sex matched healthy volunteers served as controls. N20, MEP, LLR II latencies were measured, and the CRT was calculated for each limb. The statistical comparison between patients and controls was only weakly significant by taking into account conduction times along either the afferent (N20) or the efferent (MEP) pathways. On the contrary, it turned out to be considerably significant if both branches of the transcortical sensorimotor reflex arch, together with the intracortical pathway, were simultaneously tested by means of the LLRs. Moreover, the patients showed a significantly higher CRT compared with that found in the control subjects. These findings are consistent with a prolonged intracortical delay of LLRs in the MS group and suggest the occurrence of conduction velocity slowing and/or synaptic transmission impairment along the sensorimotor intracortical pathway in MS.

Skeletal muscle characteristics of people with multiple sclerosis

OBJECTIVE

To compare the single-fiber characteristics and muscle weakness of persons with multiple sclerosis (MS) with that of healthy persons without MS.

DESIGN

Descriptive.

SETTING

A university-based exercise physiology laboratory.

PARTICIPANTS

Fourteen subjects (7 controls, 7 people with relapsing-remitting MS; Expanded Disability Status Scale median score, 6.0; range, 2.5-6.5).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Singe muscle fiber myosin heavy chain (MHC) distribution, myosin adenosine triphosphatase fiber type, and single muscle fiber cross-sectional area (CSA).

RESULTS

The distribution of MHC I, MHC IIa, MHC IIx, and total hybrid fibers (I/IIa+I/IIa/IIx+IIa/IIx) did not differ between the 2 groups. However, the distribution of MHC I/IIa/IIx fibers was greater ( P <.040) in the MS group (MS: 6% vs controls: 2%). MS subjects also had a greater proportion ( P <.002) of MHC IIx-dominant IIa/IIx fibers (MS: 46% vs controls: 13%). Single-fiber CSA and fiber type, for all fiber types, did not differ between groups.

CONCLUSIONS

These data suggest that, in general, moderately impaired MS subjects with documented muscle weakness have similar MHC and fiber-type characteristics as age-matched sedentary controls. The data indicate that the quality of skeletal muscle, with regard to MHC distribution, is unaffected by MS.

Evoked potentials for evaluation of multiple sclerosis

The role of evoked potentials (EP) in the assessment of multiple sclerosis (MS) has changed over the last decade. This is largely due to progress in imaging techniques. But while MRI has a greater diagnostic sensitivity, EP remain a useful diagnostic tool in many clinical situations. Moreover, recent studies demonstrate the utility of EP for monitoring and predicting the course of the disease in patient groups, although not yet in individuals. For these purposes, EP show better results than conventional MRI. In the near future, new developments in electrophysiology, immunology and imaging may allow to differentiate between different subtypes of MS early in the course, and consequently to tailor therapeutic measures more precisely to the individual patients.

Neurophysiological investigations in multiple sclerosis

The advent of magnetic resonance imaging techniques has greatly reduced the diagnostic value of neurophysiological tests, particularly evoked potentials, in multiple sclerosis patients, because of the higher sensitivity in revealing subclinical involvement of the central nervous system. Technical progress and new methods of investigating afferent and efferent nervous pathways would seem to increase the sensitivity in detecting neural dysfunction, but the 'clinical gain' is modest at best. More promising is the utilization of neurophysiological tests to quantify the severity of white matter involvement. Transversal and longitudinal studies have demonstrated good correlations between neurophysiological parameters and disability measures, indicating that a battery of neurophysiological tests could be useful in monitoring the disease evolution in single patients and as surrogate endpoints in clinical trials. Further studies are needed for a better definition of the applications of evoked potentials and other neurophysiological techniques. Finally, event-related potentials and advanced electroencephalogram techniques, such as coherence analysis, could provide useful information on the pathophysiology of cognitive dysfunction, so common in multiple sclerosis patients, and with a strong impact on the quality of life.

Magnetoelectric brain stimulation in the assessment of brain physiology and pathophysiology

OBJECTIVE

To review findings from transcranial magnetic stimulation (TMS)-induced motor evoked potentials in normal subjects, in various neurological diseases and with pharmacologic manipulation.

METHODS

MEDLINE was searched to identify pertinent articles and articles referenced therein were also reviewed.

RESULTS

TMS is a safe and non-invasive technique which has been used widely in the study of corticospinal and corticocortical connectivity as well as in the assessment of basal ganglia disorders, diffuse diseases, and neuropharmacology.

CONCLUSIONS

TMS motor measures have utility in examination of brain structure and function within and beyond the corticospinal tract. These measures have both research and clinical applications.

Changes in motor evoked potentials to short-interval paired transcranial magnetic stimuli in multiple sclerosis

OBJECTIVE

Paired transcranial magnetic stimuli (TMS) were applied in 8 multiple sclerosis (MS) patients with asymmetrical clinical signs and in 8 healthy controls to test the hypothesis that the circuits responsible for the generation and transmission of I-waves are abnormal in the former group

METHODS

A figure-of-8 coil discharging through a Magstim 200/Bistim configuration delivered identical stimuli at an intensity 10% above the motor threshold of the relaxed first dorsal interosseous muscle. The interstimulus intervals (ISIs) used were varied in a pseudo-randomized fashion in steps of 0.2 ms between 1.0 and 5 ms.

RESULTS

In 9 of 12 unilateral studies in the control group, a pattern of 3 peaks of increased motor evoked potential size was found at ISIs of 1.2-1.6 ms, 2.4-3.2 ms and 4.4-5.0 ms. A similar pattern was present in only 5 of 12 studies in the patients (Fisher's exact test, P = 0.1), while it was absent in all the 4 studies of the side with greater clinical involvement in patients (P = 0.01)

CONCLUSION

Our results suggest that I-wave generation is more likely to be defective in MS than in normal subjects, that this defect resides in the cortex, and that it correlates with severity of physical signs.

Recommendations for physical activity in patients with multiple sclerosis

For many years, patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system, have been advised to avoid exercise. MS is believed to be autoimmune in origin, mediated by activated T cells which penetrate the blood-brain barrier and attack myelin. The pathophysiology, with respect to function is an impairment of saltatory conduction, specifically, slowing of conduction speed and/or conduction block. Symptoms can temporarily worsen on exposure to heat or during physical exercise. Exercise programmes must be designed to activate working muscles but avoid overload that results in conduction block. Fatigue, often severe, affects about 85% of MS patients and, along with motor and sensory symptoms, results in decreased mobility and reduced quality of life. Physical activity and recreation are reduced in patients with MS. Before developing recommendations, physical activity patterns and the physical effects of MS should be assessed in individual patients. Patients may then be functionally classified. Physical activity can also be classified in a pyramid structure, with the most basic functions forming the base and the most integrated functions on top. The muscular fitness pyramid progresses through passive range of motion, active resistive, specific strengthening and integrated strength exercises Overall physical activity may be increased according to functional level by performing activities of daily living, incorporating inefficiencies into daily living, pursuing more active recreation and eventually developing a structured exercise programme. The importance of the proper exercise environment, balance and coordination issues and factors related to adherence are discussed.