Amyotrophic lateral sclerosis versus cervical spondylotic myelopathy: a study using transcranial magnetic stimulation with recordings from the trapezius and limb muscles

Novel approaches to assessing upper motor neuron dysfunction in motor neuron disease/amyotrophic lateral sclerosis: IFCN handbook chapter

Identifying upper motor neuron (UMN) dysfunction is fundamental to the diagnosis and understanding of disease pathogenesis in motor neuron disease (MND). The clinical assessment of UMN dysfunction may be difficult, particularly in the setting of severe muscle weakness. From a physiological perspective, transcranial magnetic stimulation (TMS) techniques provide objective biomarkers of UMN dysfunction in MND and may also be useful to interrogate cortical and network function. Single, paired- and triple pulse TMS techniques have yielded novel diagnostic and prognostic biomarkers in MND, and have provided important pathogenic insights, particularly pertaining to site of disease onset. Cortical hyperexcitability, as heralded by reduced short interval intracortical inhibition (SICI) and increased short interval intracortical facilitation, has been associated with the onset of lower motor neuron degeneration, along with patterns of disease spread, development of specific clinical features such as the split hand phenomenon, and may provide an indication about the rate of disease progression. Additionally, reduction of SICI has emerged as a potential diagnostic aid in MND. The triple stimulation technique (TST) was shown to enhance the diagnostic utility of conventional TMS measures in detecting UMN dysfunction in MND. Separately, sophisticated brain imaging techniques have uncovered novel biomarkers of neurodegeneration that have bene associated with progression. The present review will discuss the utility of TMS and brain neuroimaging derived biomarkers of UMN dysfunction in MND, focusing on recently developed TMS techniques and advanced neuroimaging modalities that interrogate structural and functional integrity of the corticomotoneuronal system, with an emphasis on pathogenic, diagnostic, and prognostic utility.

Features Suggestive of Coexisting Amyotrophic Lateral Sclerosis in Patients With Spinal Stenosis and Influence of Spinal Decompression

BACKGROUND

 Spinal stenosis and amyotrophic lateral sclerosis (ALS) can co-occur and both manifest as signs of dysfunction of lower and/or upper motor neurons. Few studies have identified factors that alert the diagnosis of ALS in patients with spinal stenosis, and the influence of spinal decompression surgery on ALS progression remains unclear.

OBJECTIVE

The objective of this study is to describe factors that are suggestive of an ALS diagnosis in patients with spinal stenosis and influence of spinal decompression surgery on the progression of ALS  Materials and methods: A retrospective review of the institutional ALS database and electronic medical records was performed to identify patients with coexisting diagnoses of ALS and moderate to severe cervical and/or lumbosacral spine stenosis. Identified patients were divided into two subgroups: those with spinal decompression surgery and those without. Comparisons of clinical features and progression of ALS were made between subgroups.

RESULTS

 A total of 77 patients with ALS and coexisting moderate to severe cervical or lumbosacral spine stenosis were included. Among them, 50 patients underwent spinal decompression surgery and 27 did not. In comparison to patients with spinal decompression, patients without spinal decompression surgery were seen more frequently by neurologists (74% versus 26%), had less prominent radicular pain (19% versus 50%), demonstrated more frequent bulbar signs (30% versus 8%), experienced more likely weight loss (41% versus 4%), and disclosed more noticeable axonal loss changes on electromyography. Spinal decompression surgery did not modify the progression of ALS based on ALSFRS-R score change and analysis of survival duration.

CONCLUSION

Our study identified a number of useful features that are suggestive of an ALS diagnosis when evaluating patients with spinal stenosis and may support the performance of spinal decompression surgery in a subset of selected ALS patients with symptomatic spinal stenosis.

Combined tendon reflex and motor evoked potential recordings in amyotrophic lateral sclerosis

OBJECTIVE

This retrospective (case-control) collaborative study evaluates tendon reflex recordings combined with transcranial magnetic stimulation motor evoked potentials recordings (T-MEPs) at lower limbs in amyotrophic lateral sclerosis (ALS).

METHODS

T-MEPs were recorded in 97 ALS patients distinguished according to their patellar reflex briskness. Patients' electrophysiological data were compared with values measured in 60 control patients matched for age and height. Correlations studies between parameters or with some patients' clinical characteristics were also performed.

RESULTS

The central motor conduction time yields the highest sensitivity (82%) and specificity (93%), allowing twice more upper motor neuron (UMN) dysfunction detection than clinical examination, and being more altered in late stages of the disease. The T response to MEP response amplitude ratio (T/MEP ar) is nearly as sensitive to detect ALS and better identifies abnormal hyperreflexia. It is not correlated with evolutive stage, contrarily to conduction time-related parameters. In addition, T-MEPs detect asymmetries escaping clinical examination.

CONCLUSIONS

The corticospinal conduction to lower limbs is slowed in ALS. The T/MEP ar helps deciding when patellar reflexes are abnormal in a given patient suspected of ALS.

SIGNIFICANCE

The T-MEP technique provide powerful electrophysiological biomarkers of UMN involvement in ALS. This simple and painless procedure introduces the clinically useful concept of electrophysiological hyperreflexia and might be expanded to future exploration of proximal upper limbs and bulbar territories.

Early diagnosis of amyotrophic lateral sclerosis by threshold tracking and conventional transcranial magnetic stimulation

BACKGROUND AND PURPOSE

Short-interval intracortical inhibition by threshold tracking (T-SICI) has been proposed as a diagnostic tool for amyotrophic lateral sclerosis (ALS) but has not been compared directly with conventional amplitude measurements (A-SICI). This study compared A-SICI and T-SICI for sensitivity and clinical usefulness as biomarkers for ALS.

METHODS

In all, 104 consecutive patients referred with suspicion of ALS were prospectively included and were subsequently divided into 62 patients with motor neuron disease (MND) and 42 patient controls (ALS mimics) by clinical follow-up. T-SICI and A-SICI recorded in the first dorsal interosseus muscle (index test) were compared with recordings from 53 age-matched healthy controls. The reference standard was the Awaji criteria. Clinical scorings, conventional nerve conduction studies and electromyography were also performed on the patients.

RESULTS

Motor neuron disease patients had significantly reduced T-SICI and A-SICI compared with the healthy and patient control groups, which were similar. Sensitivity and specificity for discriminating MND patients from patient controls were high (areas under the receiver operating characteristic curves 0.762 and 0.810 for T-SICI and A-SICI respectively at 1-3.5 ms). Paradoxically, T-SICI was most reduced in MND patients with the fewest upper motor neuron (UMN) signs (Spearman ρ = 0.565, p = 4.3 × 10^-6 ).

CONCLUSIONS

Amplitude-based measure of cortical inhibition and T-SICI are both sensitive measures for the detection of cortical involvement in MND patients and may help early diagnosis of ALS, with T-SICI most abnormal before UMN signs have developed. The gradation in T-SICI from pathological facilitation in patients with minimal UMN signs to inhibition in those with the most UMN signs may be due to progressive degeneration of the subset of UMNs experiencing facilitation.

Central motor conduction time reveals upper motor neuron involvement masked by lower motor neuron impairment in a significant portion of patients with amyotrophic lateral sclerosis

OBJECTIVE

We retrospectively investigated the utility of the central motor conduction time (CMCT) in detecting upper motor neuron (UMN) involvements in patients with amyotrophic lateral sclerosis (ALS).

METHODS

Fifty-two ALS patients and 12 disease control patients participated in this study. Surface electromyograms were recorded from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. We stimulated the motor cortex, brainstem, and spinal nerve using transcranial magnetic stimulation (TMS) in order to measure the cortical, brainstem, and spinal latencies. We divided the ALS patients into 2 subgroups (with UMN impairment vs. without UMN impairment) and calculated the rates of abnormal CMCT prolongation judged by their comparison with the normal ranges obtained by the measurement in the control patients.

RESULTS

The CMCTs in the FDI and TA were abnormally prolonged in over 40% of the ALS patients with UMN impairment and in nearly 30% of those without UMN impairment.

CONCLUSIONS

CMCT shows UMN dysfunction in ALS patients without clinical UMN impairment.

SIGNIFICANCE

TMS still has diagnostic utility in a significant portion of ALS patients.

Single-pulse transcranial magnetic stimulation in amyotrophic lateral sclerosis

INTRODUCTION

Transcranial magnetic stimulation (TMS) is one of the best methods to identify changes in the corticospinal tract. We used single-pulse TMS at the beginning of the disease and in the follow-up in a group of patients with amyotrophic lateral sclerosis (ALS).

METHODS

We evaluated the corticospinal tract in the bulbar, upper, and lower regions in 55 patients with ALS, and we monitored them for a period of 24 months. Data were correlated with clinical scales.

RESULTS

An increase of central motor conduction time (CMCT) was the most sensitive marker of upper motor neuron involvement. The resting motor threshold, CMCT, and the central silent period increased linearly with disease duration and upper/lower motor neuron involvement.

DISCUSSION

Transcranial magnetic stimulation could be an essential neurophysiological technique in the early phase of ALS because it has been shown to be useful in detecting subclinical upper motor neuron involvement. Multiple evaluations of several regions increase TMS sensitivity.

Epidemiology and diagnostic process of amyotrophic lateral sclerosis as distinct from myelopathy: 5-year cohort study of whole-population in South Korea

OBJECTIVE

To investigate the incidence, prevalence, and demographic factors of all amyotrophic lateral sclerosis (ALS) patients diagnosed in South Korea from 2011 to 2015, and to analyze cases misdiagnosed as myelopathy.

METHODS

The whole population registered under the Korean National Health Insurance Service (KNHIS) was applied. All 4551 patients who were registered as having ALS code from 2011 to 2015 were included. For all ALS patients, the incidence, prevalence, and demographic factors were assessed. Trends of diagnosis for myelopathy, and surgery prior to confirmation of ALS diagnosis were identified.

RESULTS

When the whole 48,135,715 KNHIS population enrolled in 2015, the incidence of ALS in 2015 was estimated to be 1.68 per 100,000 person-years, and the prevalence was 6.49 per 100,000 persons. Life expectancy of ALS can be calculated as 3.9 years after the diagnosis, and the mean age of diagnosis was 59.5 ± 13.1. A total of 1902 patients diagnosed with myelopathy before a diagnosis of ALS accounted for 0.13% of all myelopathy patients, and 41.8% of all ALS patients. It took an average of 471.7 d to confirm a diagnosis of ALS after the myelopathy diagnosis. Among the patients finally diagnosed with ALS, more patients underwent surgery for myelopathy (n = 263, 13.8%) than among patients who were diagnosed with myelopathy alone, and underwent surgery (n = 141,148, 9.8%).

CONCLUSIONS

This whole-population nationwide demographic study confirmed the data from previous studies. Clinicians should consider the possibility of ALS when making a myelopathy diagnosis, especially if the symptoms are sufficiently severe to require surgery.

Amyotrophic lateral sclerosis or not: Keys for the diagnosis

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease (MND) which prognosis is poor. Early diagnosis permit to set up immediately adapted treatment and cares. Available diagnostic criteria are based on the detection of both central and peripheral motor neuron injury in bulbar, cervical, thoracic and lumbar regions. Electrodiagnostic (EDX) tests are the key tools to identify peripheral motor neuron involvement. Needle examination records abnormal activities at rest, and looks for neurogenic pattern during muscle contraction. Motor unit potentials morphology is modified primary to recruitment. Motor evoked potentials remain the test of choice to identify impairment of central motor neurons. In the absence of diagnostic biomarker of ALS and among essential investigations of suspected MND, a careful clinical and neurophysiological work-up is essential to rule out the differential diagnosis.

Apparent diffusion coefficients distinguish amyotrophic lateral sclerosis from cervical spondylotic myelopathy

OBJECTIVE

Fifty percent of patients with amyotrophic lateral sclerosis (ALS) have cervical spondylotic myelopathy (CSM) as a complication. Because patients with ALS do not develop bulbar signs and symptoms at onset, differentiating them from patients with CSM is sometimes difficult. We aimed to determine whether the apparent diffusion coefficients (ADCs) of intracranial corticospinal tracts can be used to distinguish between patients with ALS and those with CSM.

METHODS

We evaluated 19 consecutive patients with ALS who did not have CSM by cervical MRI, 16 patients with CSM, and 11 healthy controls. We examined the mean ADCs in the precentral gyrus, the corona radiata, the posterior limbs of the internal capsule (PLIC), and the cerebral peduncle by 3T magnetic resonance imaging (MRI). The mean ADCs in the intracranial corticospinal tracts in patients with ALS were compared with those in patients with CSM.

RESULTS

The mean ADCs in the intracranial corticospinal tracts in patients with ALS were compared with those in patients with CSM (p<0.05). Additionally, the mean ADCs in the precentral gyrus, the PLIC, and the cerebral peduncle in the patients with ALS, including the patients who were initially diagnosed as having clinically possible ALS on the basis of the revised El Escorial criteria and did not develop bulbar symptoms at onset, were also higher than those in patients with CSM (p<0.05).

CONCLUSIONS

Elevated ADCs in the intracranial corticospinal tracts might be useful for distinguishing ALS from CSM in the early stage of the disease.

Few patients with neurodegenerative disorders require spinal surgery

Background:

Few patients with neurodegenerative disorders (ND) (e.g., Multiple Sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS), and Postpolio Syndrome (PPS)) require spinal surgery. Typically, their neurological symptoms and signs reflect their underlying neurologic disorders rather than structural spinal pathology reported on magnetic resonance images (MR) or computed tomographic scans (CT).

Methods:

The first author, a neurosurgeon, reviewed 437 spinal consultations performed over a 20-month period. Of 254 patients seen in first opinion (e.g., had not been seen by a spinal surgeon), 9 had MS, while 2 had ALS. Of 183 patients seen in second opinion (e.g., prior spinal surgeons recommended surgery), 4 had MS, 2 had ALS, and 1 had PPS. We performed this study to establish how often patients with ND, seen in first or second opinion, require spinal surgery. We focused on whether second opinions from spinal surgeons would limit the number of operations offered to these patients.

Results:

Two of 11 patients with ND seen in first opinion required surgery. The first patient required a C5-7 laminectomy/C2-T2 fusion, followed by a L2-S1 laminectomy/L5S1 fusion. The second patient required a L2-L3 laminectomy/diskectomy/fusion. However, none of the seven patients seen in second opinion, who were previously told by outside surgeons they needed spinal surgery, required operations.

Conclusions:

Few patients with neurodegenerative syndromes (MS, ALS, PPS) and reported “significant” spondyloitic spinal disease interpreted on MR/CT studies required surgery. Great caution should be exercised in offering patients with ND spinal surgery, and second opinions should be encouraged to limit “unnecessary” procedures.

Differential diagnosis for cervical spondylotic myelopathy: literature review

STUDY DESIGN

Literature review.

OBJECTIVE

To identify case series that have been confused with cervical spondylotic myelopathy (CSM) to develop a comprehensive differential diagnosis.

SUMMARY OF BACKGROUND DATA

Myelopathy can be caused by a number of different etiologies. In those patients with CSM, the presentation is not always clear. Distinct radiographical and clinical characteristics, which are not always obvious, aid in arriving at the correct diagnosis.

METHODS

A PubMed search was done to identify reports written in English describing conditions that may present in a manner similar to CSM to differentiate them from CSM. Material from review articles and relevant textbooks was also considered. Information regarding the number of patients, the specific diagnosis presenting as myelopathy, the diagnostic findings, and the method(s) for distinguishing CSM from the initial diagnosis was abstracted from included articles. Salient features of the conditions were summarized.

RESULTS

A total of 35 citations (totaling 474 patients) that reported on diagnoses confused with CSM based on clinical presentation were included. All were case reports or small case series. The differential diagnoses were organized into 7 categories: congenital/anatomic, degenerative, neoplastic, inflammatory/autoimmune, idiopathic, circulatory, and metabolic. The primary conditions in the differential included amyotrophic lateral sclerosis, multiple sclerosis, syringomyelia, and spinal tumors.

CONCLUSION

In the vast majority of cases, magnetic resonance imaging was an invaluable tool in determining the correct diagnosis. Electrodiagnostic studies, cerebrospinal fluid profile, unique symptomatology, and consideration of patient demographics can also aid in the diagnosis. Bilateral sensory complaints in the hands are suspicious for cervical cord pathology and MR imaging of the same should be done even if the electromyography/nerve conduction studies (NCS) suggest bilateral carpal tunnel syndrome. SUMMARY STATEMENTS: Physical exam findings are not always consistent with severity of disease in CSM; therefore, correlation to plain radiographs, MRI, and patient symptomatology is essential for arriving at the correct diagnosis. In some cases where these studies are still equivocal, use of other studies should be considered including electrodiagnostic studies as well as cerebrospinal fluid examination.

Rapidly progressive amyotrophic lateral sclerosis initially masquerading as a demyelinating neuropathy

Rare cases of demyelinating neuropathy have been described in association with amyotrophic lateral sclerosis (ALS). We report two patients with typical ALS whose initial electroneuromyographic (ENMG) presentation could suggest the existence of a process of motor nerve fiber demyelination. However, subsequent ENMG examinations and the fatal course of the disease in a few months rather supported severe ongoing axonal degeneration at the origin of motor nerve conduction abnormalities. Repeated examinations could be required to distinguish between ENMG features of concomitant demyelinating neuropathy and rapidly progressive motor neuron loss in ALS.

Central motor conduction time

Central motor conduction time (CMCT) is the time taken for neural impulses to travel through the central nervous system on their way to the target muscles. When the motor cortex is stimulated with transcranial magnetic stimulation (TMS), CMCT is calculated by subtracting the peripheral conduction time from the motor evoked potential latency elicited by motor cortical TMS. CMCT in infants and children reaches adult level at about age of 6 years for the lower limbs. The alterations of CMCT in various neurological conditions are reviewed in this chapter. Prolongation of CMCT occurs due to slowing of conduction through rapidly conducting corticospinal fibers, as seen in various disorders such as demyelinating diseases (multiple sclerosis, MS), amyotrophic lateral sclerosis, structural lesions in the corticospinal tract such as stroke and compressive myelopathy, and neurodegenerative disorders including multiple system atrophy and progressive supranuclear palsy. As CMCT is prolonged in certain clinical conditions, it is of diagnostic value in some neurological disorders such as myelopathy, amyotrophic lateral sclerosis, and MS when used together with other clinical and electrophysiological measures. It could also be used as a prognostic marker in some of neurological conditions, such as myelopathy and MS.

Discharge rate modulation of trapezius motor units differs for voluntary contractions and instructed muscle rest

This study examined discharge rate modulation at respiratory (0-0.5 Hz) and beta (16-32 Hz) frequencies in trapezius motor units active during voluntary contractions and during periods of instructed rest under conditions of low and high psychosocial stress. In separate sessions, single motor unit activity was recorded from the trapezius muscle of healthy women during low-intensity voluntary contractions and during periods of instructed muscle rest that followed voluntary contractions. The level of psychosocial stress during periods of instructed muscle rest was manipulated using a verbal math task combined with social evaluative threat which increased perceived anxiety, heart rate, and blood pressure (P ≤ 0.002). Discharge rate modulation was quantified by the mean power of motor unit discharge rate profiles within frequency bands of interest. Under low stress conditions, motor units active during instructed rest had greater power at 0-0.5 Hz (P = 0.002) and less power at 16-32 Hz (P = 0.009) compared to those active during voluntary contraction. Exposure to the stressor increased the amount of motor unit activity during instructed rest (P = 0.021) but did not alter the power of discharge rate modulation at 0-0.5 Hz (P = 0.391) or 16-32 Hz (P = 0.089). These results indicate that sustained motor unit activity during periods of instructed muscle rest has a lesser contribution from inputs at beta frequencies and a greater contribution from inputs at respiratory frequencies than present during low-intensity voluntary contractions. Furthermore, increases in motor unit activity when exposed to stressors during periods of instructed rest are not caused by changes in inputs at respiratory or beta frequencies.

Prospective, blind study of the triple stimulation technique in the diagnosis of ALS

OBJECTIVE

To evaluate the diagnostic yield of magnetic cortical stimulation with the triple stimulation technique (TST) to identify upper motor neuron (UMN) involvement in patients suspected of having ALS.

METHODS

Fifty-nine patients were recruited to undergo TST in addition to the standard work-up for suspected motor neuron disease. TST combines transcranial magnetic stimulation of the motor cortex with collision studies, which results in a higher sensitivity in detecting UMN involvement. Primary outcome was the number of abnormal TST results in patients with possible ALS. The positivity rate was converted to the number needed to test with TST (NN-TST) for one extra diagnosis of ALS.

RESULTS

Fifty patients underwent TST. In the total group (n=59), 18 patients had a motor neuron disorder but did not fulfil criteria for 'probable' or 'definite' ALS. In four of these patients TST was abnormal (NN-TST, 4.5). One TST was erroneously interpreted as abnormal. TST findings were normal in inclusion body myositis and peripheral nerve disorders.

CONCLUSION

This prospective and blind study confirms open studies of TST in the evaluation of ALS. We suggest that TST can be used to arrive at a diagnosis of 'probable' or 'definite' ALS in patients lacking UMN signs in the upper extremities.

Trapezius motor evoked potential in evaluations of corticospinal tract lesions

BACKGROUND

We wanted to know whether trapezius motor evoked potentials (MEPs) are helpful in the evaluation of corticospinal (CS) lesions above the fifth cervical segment (C5) and compared trapezius MEP measurements in patients with and without radiological evidence of CS lesions.

METHODS

Trapezius MEPs were routinely recorded in all MEP studies performed in our hospital. Patients who had MEP studies as well as brain and cervical spine imaging were retrospectively assigned to two groups. Group 1 had radiological evidence of CS lesion above the level of C5 whilst group 2 did not.

RESULTS

Forty-nine patients were included in the study. Twenty-eight patients were assigned to group 1 and 21 patients to group 2. The frequencies of abnormal values in the two groups were compared. Twelve (43%) patients in group 1 and three (14%) in group 2 had prolonged MEP latencies. Thirteen patients in group 1 had indentation or impingement of the cervical cord by intervertebral discs as the only relevant radiological abnormality. Seven (54%) of these patients were found to have prolonged trapezius MEP latencies, providing functional correlates to the radiological abnormalities.

CONCLUSIONS

Our study gives evidence to the usefulness of trapezius MEP study in the evaluation of CS lesions.

Differential control of the scapulothoracic muscles in humans

The control of the scapulothoracic muscles trapezius (Tr) and serratus anterior (SA) has been examined in normal human subjects. Electromyographic recordings were made from the SA and Tr muscles (upper trapezius UTr, lower trapezius LTr) using surface electrodes placed bilaterally. Magnetic stimulation of the motor cortex and electrical stimulation of peripheral nerves were used to examine their descending and reflex control. The average optimal site of cortical stimulation was found to be the same for SA, UTr and LTr (an approximate centre of gravity of -0.6 cm, 3.7 cm where the centre of gravity is expressed as the mean anterio-posterior position, the mean medio-lateral position). Some asymmetry in the cortical representation of UTr was found in each individual tested. Magnetic stimulation evoked bilateral MEPs in Tr (latency contralateral (c) UTr 8.5 +/- 1.6 ms, ipsilateral (i) UTr 19.0 +/- 2.7 ms) but only contralateral responses were evoked in SA (11.2 +/- 2.6 ms). Electrical stimulation of the long thoracic nerve at two sites was used to examine homonymous and heteronymous reflexes of SA, while electrical stimulation of cervical nerve of C3/4 was used to examine the heteronymous reflexes of Tr. Ipsilateral SA H reflexes were evoked at a latency of 9.9 +/- 0.8 ms (proximal site) and 10.8 +/- 1.2 ms (distal site). No group I reflexes were evoked from SA to its contralateral homologue. No group I reflexes were evoked between Tr and SA. Finally, cross-correlation of activity from the Tr muscle pairs and the SA muscle pair revealed that the motoneurones of the Tr muscles share some common presynaptic input whereas there was no detectable common presynaptic input to the SA muscle pair. This study extends and consolidates knowledge regarding the neural control of trapezius and for the first time explores the neural control of SA. The study demonstrates a contrasting bilateral control of Tr and SA. These patterns of connections are discussed in relation to the contrasting bilateral functional roles of these muscles.

Transcallosal inhibition in amyotrophic lateral sclerosis

OBJECTIVE

Assessment of upper motor neuron (UMN) involvement is essential for the diagnosis of amyotrophic lateral sclerosis (ALS). In a number of ALS cases, mirror movements (MM) suggest an involvement of transcallosal fibre tracts in conjunction with UMN involvement. The present study analysed whether deficient transcallosal inhibition (TI) tested by TMS enables detection of cortical affection in ALS, even at early stages of the disease.

METHODS

In three patients with definite ALS and 12 patients with early ALS (aged 64.1+/-7.8 years) TMS investigation included analysis of contralateral (cMEP) and ipsilateral (iMEP) motor evoked potentials as well as measurement of TI (latency, duration) with recording from both first dorsal interosseus muscles.

RESULTS

Clinical UMN signs were present in four patients. 83.3% of patients showed a pathological TI (prolongation or loss of TI). Five out of eight ALS patients showing a pathological TI had no clinical UMN signs. Two of these patients showed MM. One patient displayed also pathological findings in TI investigation.

CONCLUSIONS

Our findings suggest a functional deficit of transcallosal fibre tracts even at early stages of the disease still lacking clinical UMN signs.

SIGNIFICANCE

Measurement of TI tested by TMS can detect an involvement of the cortical output system in ALS and may be helpful in an early assessment of the diagnosis.

Clinical utility of trapezius muscle studies in the evaluation of amyotrophic lateral sclerosis

Needle electromyography (EMG) and determining the motor evoked potential (MEP) of the genioglossus (tongue) are difficult to perform in evaluation of the craniobulbar region in patients with amyotrophic lateral sclerosis (ALS). Needle EMG and MEP determination in the upper trapezius were carried out in 17 consecutive ALS patients. The needle EMG parameters recorded included abnormal spontaneous activity and motor unit action potential morphology. An upper motor neuron lesion was presumed when either response to cortical stimulation was absent, or the central conduction time was delayed (>mean + 2 SD). Of the 12 patients with limb-onset ALS, using needle EMG, 11 were found to have abnormalities in the upper trapezius, and only five in the tongue. Three of the six patients with isolated limb involvement had abnormal MEP findings. In conclusion, electrophysiological studies of the upper trapezius are useful in ALS patients without bulbar symptoms.

Optimising the detection of upper motor neuron function dysfunction in amyotrophic lateral sclerosis?a transcranial magnetic stimulation study

Evidence of upper motor neuron (UMN) dysfunction is essential in making the diagnosis of amyotrophic lateral sclerosis (ALS). Central motor conduction (CMC) abnormalities detected using transcranial magnetic stimulation (TMS) are presumed to reflect UMN dysfunction. CMC is, however, often normal in patients with classical sporadic ALS. The aim of the study was to determine whether the utility of the CMC measure in ALS could be enhanced. We measured CMC to four pairs of muscles (abductor digiti minimi (ADM), biceps, vastus medialis (VM) and abductor hallucis (AH) in 20 controls and 25 ALS patients. The commonest abnormality detected in the ALS patients was an absent MEP, found in 11 patients (44 %) and in 25 of 200 muscles examined. Studying a minimum of three muscles increased the probability of detecting UMN dysfunction. Weakness in the muscle as well as selecting a distal rather than a proximal muscle was significantly associated with an abnormal CMC. Interside differences in CMC were significantly more pronounced in the patient group. In 30% of patients a significant interside difference in AH CMC time was the sole abnormality, suggesting mild UMN dysfunction on the side with the longer CMC.

The triple stimulation technique to study central motor conduction to the lower limbs

OBJECTIVE

To quantify the percentage of motor units of a foot muscle that can be activated by transcranial magnetic stimulation (TMS) in normal subjects and patients.

METHODS

We adapted the recently described triple stimulation technique (TST) for recordings from abductor hallucis (AH). Conventional motor evoked potentials (MEPs) of this muscle are usually small and variable in shape, because of an important temporal desynchronization of the TMS induced spinal motor neuron discharges. The TST allows 'resynchronization' of these discharges and thereby a quantification of the proportion of motor units activated by TMS. The lower limb (LL-) TST was applied to 33 sides of 18 normal subjects and 51 sides of 46 patients with multiple sclerosis, amyotrophic lateral sclerosis, or spinal cord disorders.

RESULTS

In healthy subjects, the LL-TST demonstrated that TMS achieves activation of virtually all motor neurons supplying the AH. In 33 of 51 patient sides, abnormal LL-TST responses suggested corticospinal conduction failures of various degrees. The LL-TST was 2.54 times more sensitive to detect central conduction failures than the conventional LL-MEPs. Combining the LL-TST with TST of the upper limbs further increased the sensitivity to detect a conduction failure by 1.50 times.

CONCLUSION

The LL-TST markedly improves the examination of corticospinal pathways.