Transcranial magnetic stimulation enhances the specificity of multiple sclerosis diagnostic criteria: a critical narrative review

Background

Multiple sclerosis (MS) is an immune-mediated neurodegenerative disease that involves attacks of inflammatory demyelination and axonal damage, with variable but continuous disability accumulation. Transcranial magnetic stimulation (TMS) is a noninvasive method to characterize conduction loss and axonal damage in the corticospinal tract. TMS as a technique provides indices of corticospinal tract function that may serve as putative MS biomarkers. To date, no reviews have directly addressed the diagnostic performance of TMS in MS. The authors aimed to conduct a critical narrative review on the diagnostic performance of TMS in MS.

Methods

The authors searched the Embase, PubMed, Scopus, and Web of Science databases for studies that reported the sensitivity and/or specificity of any reported TMS technique compared to established clinical MS diagnostic criteria. Studies were summarized and critically appraised for their quality and validity.

Results

Seventeen of 1,073 records were included for data extraction and critical appraisal. Markers of demyelination and axonal damage-most notably, central motor conduction time (CMCT)-were specific, but not sensitive, for MS. Thirteen (76%), two (12%), and two (12%) studies exhibited high, unclear, and low risk of bias, respectively. No study demonstrated validity for TMS techniques as diagnostic biomarkers in MS.

Conclusions

CMCT has the potential to: (1) enhance the specificity of clinical MS diagnostic criteria by "ruling in" true-positives, or (2) revise a diagnosis from relapsing to progressive forms of MS. However, there is presently insufficient high-quality evidence to recommend any TMS technique in the diagnostic algorithm for MS.

Abnormal cortical excitability in patients with spinocerebellar ataxia type 12

BACKGROUND

Spinocerebellar ataxia type 12 (SCA-12) is an uncommon autosomal dominant cerebellar ataxia characterized by action tremors in the upper limbs, dysarthria, head tremor, and gait ataxia. We aimed to evaluate the motor cortical excitability in patients with SCA-12 using transcranial magnetic stimulation (TMS).

METHODS

The study was done in the department of Neurology at the National Institute of Mental Health and Neuro Sciences (NIMHANS), Bangalore. Nine patients with SCA-12 (2 females) and 10 healthy controls (2 females) were included in the study. TMS was performed in all the subjects and various parameters such as resting motor threshold (RMT), central motor conduction time (CMCT) and contralateral silent period (cSP) were recorded. The left motor cortex was stimulated and the recording was done from right first dorsal interossei muscle. The severity of ataxia was assessed using the scale for assessment and rating in ataxia (SARA).

RESULTS

The mean age of the patients was 58.11 ± 7.56 years mean age at onset: 51.67 ± 4.18 years. The mean duration of illness was 9.44 ± 4.88 years. The mean SARA score was 13.83 ± 3.60. Patients with SCA-12 had significantly increased RMT (88.80 ± 12.78 %) compared to HC (44.90 ± 9.40 %, p < 0.05). A significantly prolonged CMCT was observed in patients (13.70 ± 2.52 msec) compared to HC (7.31 ± 1.21 msec, p < 0.05). In addition, cSP was significantly increased in SCA-12 patients (144.43 ± 25.79 msec) compared to HC (82.14 ± 28.90 msec, p < 0.05).

CONCLUSIONS

Patients with SCA-12 demonstrate a reduced cortical excitability and increased cortical inhibition suggesting an increase in the GABAergic neurotransmission.

Comparison of the electrophysiological characteristics of tight filum terminale and tethered cord syndrome

PURPOSE

This study aims to characterize tight filum terminale (TFT) in motor evoked potential (MEP) testing by comparing TFT patients with both tethered cord syndrome (TCS) patients and healthy subjects.

METHODS

Fifty TFT patients, 18 TCS patients, and 35 healthy volunteers participated in this study. We recorded MEPs following transcranial magnetic stimulation from the bilateral abductor hallucis muscles as well as compound muscle action potentials and F-waves evoked by electrical stimulation of the tibial nerve from the bilateral abductor pollicis brevis muscles. The peripheral conduction time (PCT) was calculated from the latency of the compound action potential and F-wave. Furthermore, the central motor conduction time (CMCT) was calculated by subtracting PCT from MEP latency.

RESULTS

TFT and TCS patients had a significantly longer MEP latency than healthy subjects. PCT in TFT patients was significantly longer than those in TCS patients or healthy subjects. Using the cutoff values for PCT, we were able to diagnose patients with TFT patients with a sensitivity of 72.0% and a specificity of 91.4%.

CONCLUSION

Prolonged PCT in the MEP test may be a useful indicator for TFT and suggests that MEP may be used as an adjunct diagnostic tool for TFT.

Radiological factors associated with the severity of corticospinal tract dysfunctions for cervical spondylotic myelopathy: An analysis of the central motor conduction time and kinematic CT myelography

Patients with cervical spondylotic myelopathy (CSM) often exhibit symptoms in clinical practice, particularly the elderly, whose lower extremity functions are more likely to deteriorate; however, the underlying mechanisms currently remain unclear. The present study aimed to elucidate the relationship between the neurological severity of CSM based on an electrophysiological examination and radiological findings. Eighty-six patients with CSM were examined using kinematic CT myelography. The cross-sectional area of the spinal cord and dynamic changes in the spinal cord were measured at the affected level. The central motor conduction time (CMCT) using transcranial magnetic stimulation was calculated as follows: motor evoked potential latency - (compound muscle action potential latency + F latency - 1)/2 (ms). A multiple logistic regression analysis was performed to identify the radiological parameters associated with severe lower limb dysfunction. CMCT in the upper limbs correlated with spinal cord compression during neck extension, while that in the lower limbs correlated with a larger C2-7 sagittal vertical axis, cervical lordosis, a small C2-7 range of motion (ROM), and spinal cord compression during neck flexion. In a multiple logistic regression analysis, significant risk factors specific for severe lower limb dysfunction were greater anterior spondylolisthesis during neck extension (P = 0.006, OR: 2.53, 95%CI: 1.13-2.07) and small C2-7 ROM in neutral to flexion (P = 0.035, OR: 0.67, 95%CI: 0.52-0.88). Imaging findings affect upper and lower extremity functions in specific manners. Cervical stiffness or anterior compression factors may be associated with the deterioration of lower limb function.

Relationship Between Motor Function, DTI, and Neurophysiological Parameters in Patients with Stroke in the Recovery Rehabilitation unit

OBJECTIVES

We investigated the relationship between pyramidal tract evaluation indexes (i.e., diffusion tensor imaging, transcranial magnetic stimulation (TMS)-induced motor-evoked potential (MEP), and central motor conduction time (CMCT) on admission to the recovery rehabilitation unit) and motor functions at discharge in patients with ischemic or hemorrhagic stroke.

MATERIALS AND METHODS

Seventeen patients were recruited (12 men; 57.9 ± 10.3 years). The mean fractional anisotropy (FA) values of the right and left posterior limbs of the internal capsule were estimated using a computer-automated method. We determined the ratios of FA values in the affected and unaffected hemispheres (rFA), TMS-induced MEP, and the ratios of CMCT in the affected and unaffected hemispheres (rCMCT) and examined their association with motor functions (Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT)) at discharge.

RESULTS

Higher rFA values of the posterior limb of the internal capsule on admission to the recovery rehabilitation unit led to a better recovery of upper limb function (FMA: r = 0.78, p < 0.001; ARAT: r = 0.74, p = 0.001). Patients without MEP had poorer recovery of upper limb function than those with MEP (FMA: p < 0.001; ARAT: p = 0.001). The higher the rCMCT, the poorer the recovery of upper limb function (ARAT: r = -0.93, p < 0.001). However, no association was observed between the pyramidal tract evaluation indexes and recovery of lower limb motor function.

CONCLUSIONS

Evaluating the pyramidal tract is useful for predicting upper limb function prognosis, but not for lower limb function prognosis.

Understanding hyper-reflexia in acute motor axonal neuropathy (AMAN)

Hyper-reflexia is occasionally seen in acute motor axonal neuropathy (AMAN), but its pathophysiology is unclear. We report a patient with AMAN following Campylobacter jejuni enteritis, who showed generalized hyper-reflexia, bilateral Hoffmann sign and right Babinski sign. MRI and transcranial magnetic stimulation of the motor cortex disclosed no corticospinal tract involvement. An extensive electrophysiological investigation documented α-motoneuron hyperexcitability and dysfunction of the interneuronal inhibitory circuits in the spinal anterior horn. We propose an immune-mediated damage of the spinal inhibitory interneuronal network as possible mechanism inducing hyper-reflexia in AMAN.

A patient with McLeod syndrome showing involvement of the central sensorimotor tracts for the legs

Background

McLeod syndrome is a rare X-linked recessive acanthocytosis associated with neurological manifestations including progressive chorea, cognitive impairment, psychiatric disturbances, seizures, and sensorimotor axonal polyneuropathy. However, no studies have investigated the functioning of central sensorimotor tracts in patients with McLeod syndrome.

Case presentation

A 66-year-old man had experienced slowly progressive chorea and gait disturbance due to lower limb muscle weakness since his early fifties. Blood examinations showed erythrocyte acanthocytosis and the reduction of Kell antigens in red blood cells. Brain magnetic resonance imaging showed atrophy of the bilateral caudate nuclei and putamen. The diagnosis of McLeod syndrome was confirmed by the presence of a mutation of the XK gene on the X chromosome. Somatosensory-evoked potential and transcranial magnetic stimulation studies demonstrated that the central sensory and motor conduction times were abnormally prolonged for the lower extremity but normal for the upper extremity.

Conclusions

This is the first report of the involvement of the central sensorimotor tracts for the legs in a patient with McLeod syndrome. The clinical neurophysiological technique revealed the central sensorimotor tracts involvements clinically masked by neuropathy.

Clinical Utility of Longitudinal Measurement of Motor Threshold in Wilson's Disease

This study describes the longitudinal changes of resting motor threshold (RMT) and central motor conduction time (CMCT) in 18 patients with Wilson's disease (WD). The RMT, CMCT, and Global Assessment Scale for Wilson Disease (GAS-WD) were measured at baseline and at follow-up after 12.94 ± 7.23 months. There was a significant decrease in the RMT (72.11 ± 18.62 vs. 63.7 ± 15.52%; p-value = 0.002) and GAS-WD scores (14.38 ± 5.35 vs. 9.77 ± 6.47 ms; p-value = 0.04). CMCT did not improve despite chelation therapy. Hence, RMT may serve as a marker of chelation efficacy in WD.

Progression of corticospinal tract dysfunction in pre-ataxic spinocerebellar ataxia type 2: A two-years follow-up TMS study

OBJECTIVE

Corticospinal tract (CST) dysfunction is common in the pre-ataxic stage of spinocerebellar ataxia type 2 (SCA2) but quantitative assessment of its progression over time has not been explored. The aim of this study was to quantify the progression of CST dysfunction in pre-ataxic SCA2 using transcranial magnetic stimulation (TMS).

METHODS

Thirty-three pre-ataxic SCA2 mutation carriers and a 33 age- and gender-matched healthy controls were tested at baseline and 2-years follow-up by standardized clinical exams, validated clinical scales, and TMS.

RESULTS

Pre-ataxic SCA2 mutation carriers showed a significant increase of resting motor thresholds (RMT) to abductor pollicis brevis (APB) and tibialis anterior (TA) muscles, and of central motor conduction time (CMCT) to TA at 2-years follow-up, over and above changes in healthy controls. The changes in the pre-ataxic SCA2 mutation carriers were independent of the presence of clinical signs of CST dysfunction at baseline, and independent of conversion to clinically definite SCA2 at 2-years follow-up.

CONCLUSIONS

TMS markers of CST dysfunction progress significantly during the pre-ataxic stage of SCA2.

SIGNIFICANCE

TMS measures of CST dysfunction may provide biomarkers of disease progression prior to clinical disease expression that have potential utility for monitoring neuroprotective therapies in future clinical trials.

Utility of the central motor conduction time recorded from the abductor pollicis brevis and the abductor digiti minimi muscles in patients with C6-7 myelopathy

OBJECTIVE

Central motor conduction time (CMCT) recorded from the abductor pollicis brevis (CMCT-APB) and abductor digiti minimi (CMCT-ADM) muscles may enable the evaluation of patients with C6-7 myelopathy. CMCT is more useful for the evaluation of the function of spinal cord than magnetic resonance imaging (MRI) findings. CMCT may be associated with age and height. However, there are few reports regarding CMCT-APB in normal subjects. This study aimed to investigate the relationships between age, height, and conduction parameters in normal subjects to assess the effectiveness of using CMCT-APB and CMCT-ADM for the evaluation of patients with C6-7 and C7-T1 myelopathy.

DESIGN

Retrospective study.

METHODS

Fifteen patients with cervical compressive myelopathy at C6-7 (11 patients) or C7-T1 (4 patients) level were enrolled. The control group consisted of 150 normal subjects (mean age 45.8±17.0 years; mean height 163.6±8.9 cm). Motor evoked potentials induced by transcranial magnetic stimulation and F-waves were used to determine CMCT.

OUTCOME MEASURES

CMCT-APB, CMCT-ADM.

RESULTS

The normative values of CMCT-APB and CMCT-ADM were 5.3±0.7 ms and 5.2±0.8 ms, respectively. CMCT-APB was significantly longer than CMCT-ADM for patients with C6-7 myelopathy (P < 0.05). Neither of the CMCTs for those with C7-T1 myelopathy were significantly different from those of controls, but CMCT-APB was more prolonged than CMCT-ADM in patients with C6-C7 myelopathy.

CONCLUSIONS

CMCTs improve the accuracy of the diagnosis of myelopathy by pinpointing the lesion in combination with MRI imaging. Selective CMCT-APB prolongation may be seen in patients with C6-7 myelopathy but not C7-T1 myelopathy.

Effects of differences in age and body height on normal values of central motor conduction time determined by F-waves

OBJECTIVES

To investigate the effect on central motor conduction time (CMCT) based on the relationship between age and height in normal subjects.

DESIGN

Retrospective study.

METHODS

One hundred and ninety nine normal subjects (107 men and 92 women; mean age 39.0 ± 16.4 years; mean height 164.5 ± 8.8 cm) participated in the study. The approximate ages of subjects were as follows: 82 (20-29 years old), 32 (30-39 years old), 32 (40-49 years old), 28 (50-59 years old), and 25 (≧60 years old). The heights of 9, 49, 79, 53, and 9 subjects were <150 cm, 150-160 cm, 160-170 cm, 170-180 cm, and >180 cm, respectively. CMCT- abductor digiti minimi (ADM) and abductor hallucis (AH) were calculated by subtracting the peripheral motor conduction time (PMCT) from the onset latency of motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation. PMCT was calculated from the latencies of the compound muscle action potentials (CMAPs) and F-waves as follows: (latency of CMAPs + latency of F-waves -1)/2.

OUTCOME MEASURES

CMCT-ADM and CMCT-AH.

RESULTS

The normative values were 5.2 ± 0.8 ms and 11.8 ± 1.3 ms for CMCT-ADM and CMCT-AH, respectively. CMCT-ADM was not significantly correlated with age (P = 0.196) and body height (P = 0.158). CMCT-AH had significantly positive, linear correlations with age and body height (CMCT-AH = 0.014 × age + 10.971, P = 0.011, R = 0.179 and CMCT-AH = 0.026 × body height + 7.158, P = 0.010, R = 0.182).

CONCLUSIONS

We suggest normative values of 3.2-7.2 ms in CMCT-ADM for subjects exerting slight effort on ADM regardless age and body height. CMCT-AH had significantly positive, linear correlations with age and body height.

Transcranial magnetic stimulation in the semi-quantitative, pre-operative assessment of patients undergoing spinal deformity surgery

PURPOSE

To compare measurements of motor evoked potential latency stimulated either magnetically (mMEP) or electrically (eMEP) and central motor conduction time (CMCT) made pre-operatively in conscious patients using transcranial and intra-operatively using electrical cortical stimulation before and after successful instrumentation for the treatment of adolescent idiopathic scoliosis.

METHODS

A group initially of 51 patients with adolescent idiopathic scoliosis aged 12-19 years was evaluated pre-operatively in the outpatients' department with transcranial magnetic stimulation. The neurophysiological data were then compared statistically with intra-operative responses elicited by transcranial electrical stimulation both before and after successful surgical intervention. MEPs were measured as the cortically evoked compound action potentials of Abductor hallucis. Minimum F-waves were measured using conventional nerve conduction methods and the lower motor neuron conduction time was calculated and this was subtracted from MEP latency to give CMCT.

RESULTS

Pre-operative testing was well tolerated in our paediatric/adolescent patients. No neurological injury occurred in any patient in this series. There was no significant difference in the values of mMEP and eMEP latencies seen pre-operatively in conscious patients and intra-operatively in patients under anaesthetic. The calculated quantities mCMCT and eCMCT showed the same statistical correlations as the quantities mMEP and eMEP latency.

CONCLUSIONS

The congruency of mMEP and eMEP and of mCMCT and eCMCT suggests that these measurements may be used comparatively and semi-quantitatively for the comparison of pre-, intra-, and post-operative spinal cord function in spinal deformity surgery.

Evaluation of the motor cortical excitability changes after ischemic stroke

Background:

We evaluated progressive changes in excitability of motor cortex following ischemic stroke using Transcranial Magnetic Stimulation (TMS).

Materials and Methods:

Thirty-one patients (24 men, 7 women; age 37.3 ± 8.2 years) were recruited and TMS was performed using Magstim 200 stimulator and a figure-of-eight coil. Resting motor threshold (RMT) was recorded from affected and unaffected hemispheres and motor evoked potential (MEP) was recorded from contralateral FDI muscle. Central motor conduction time (CMCT) was calculated using F wave method. All measurements were done at baseline (2^nd), 4^th, and 6^th week of stroke.

Results: Affected hemisphere:

MEP was recordable in 3 patients at baseline (all had prolonged CMCT). At 4 weeks, MEP was recordable in one additional patient and CMCT remained prolonged. At 6 weeks, CMCT normalized in one patient. RMT was recordable (increased) in 3 patients at baseline, in one additional patient at 4 weeks, and reduced marginally in these patients at 6 weeks.

Unaffected hemisphere:

MEP was recordable in all patients at baseline, and reduced significantly over time (2^nd week 43.52 ± 9.60, 4^th week 38.84 ± 7.83, and 6^th week 36.85 ± 7.27; P < 0.001). The CMCT was normal and remained unchanged over time.

Conclusion:

The increase in excitability of the unaffected motor cortex suggests plasticity in the post-stroke phase.

Corticospinal tract and pontocerebellar fiber of central pontine myelinolysis

Central pontine myelinolysis is a rare neurologic disorder that is defined by demyelination of longitudinally descending tracts and transversly crossing fibers in the basis pontis. Frequently observed clinical manifestations of this disorder include sudden weakness, dysphagia, loss of consciouness and locked-in syndrome. However, there have been a few studies that reported a benign course of this disease, which include cerebellar signs, such as ataxia, intention tremor, and dysarthria. Here we report on a 53-year-old male with a history of liver cirrhosis who showed the cerebellar type of central pontine myelinolysis. The patient was diagnosed with central pontine myelinolysis based on clinical presentations and magnetic resonance imaging findings after a liver transplantation. Conventional magenetic resonance imaging (MRI) revealed the preservation of the corticospinal tract and abnormal pontocerebellar fibers. However, these findings were not sufficient to define the pathophysiology of our patient. Electrophysiologic analysis and diffusion tensor imaging (DTI) were performed to investigate cerebellar signs in this case. Delayed central motor conduction time (CMCT) to the tibialis anterior muscle with transcranial magnetic stimulation (TMS) was observed, which indicated demyelination of the corticospinal tract. Also, diffusion tensor imaging showed abnormal pontocerebellar fibers, which might have been caused by cerebellar dysfunction in our patient. A combination of TMS and DTI was also used to determine the pathophysiology of this disease.