Pattern of involvement in the cervical segments in the early stage of motor neurone disease: a single fibre EMG study

Muscle Fiber Diameter and Density Alterations after Stroke Examined by Single-Fiber EMG

This study presents single-fiber electromyography (EMG) analysis for assessment of paretic muscle changes after stroke. Single-fiber action potentials (SFAPs) were recorded from the first dorsal interosseous (FDI) muscle bilaterally in 12 individuals with hemiparetic stroke. The SFAP parameters, including the negative peak duration and the peak-peak amplitude, were measured and further used to estimate muscle fiber diameter through a model based on the quadratic function. The SFAP parameters, fiber density, and muscle fiber diameter derived from the model were compared between the paretic and contralateral muscles. The results show that SFAPs recorded from the paretic muscle had significantly smaller negative peak duration than that from the contralateral muscle. As a result, the derived muscle fiber diameter of the paretic muscle was significantly smaller than that of the contralateral muscle. The fiber density of the paretic muscle was significantly higher than that of the contralateral muscle. These results provide further evidence of remodeled motor units after stroke and suggest that paretic muscle weakness can be due to both complex central and peripheral neuromuscular alterations.

Physiology of the fasciculation potentials in amyotrophic lateral sclerosis: which motor units fasciculate?

We set out to study whether in amyotrophic lateral sclerosis (ALS) fasciculation potentials (FPs) arise from the most excitable motor units (MUs). We studied 70 patients with ALS and 18 subjects with benign fasciculation syndrome (BFS). Of the 56 eligible ALS patients, 31 had signs of reinnervation in the right first dorsal interosseous muscle selected for study, and 25 did not. Two needle electrodes were placed in different MUs in each studied muscle. We defined the most excitable MU as that first activated by minimal voluntary contraction. In muscles without reinnervation, the recording site with most frequent FPs had a higher probability of showing the first recruited MU (p < 0.001). No significant difference was found in other patients or in BFS subjects. In very early affected muscles, fasciculating MUs are the most likely to be recruited volitionally. This probably represents hyperexcitability at lower motor neuronal level.

The onset of amyotrophic lateral sclerosis

Two patients in whom both the neurological examination and electromyography (EMG) were normal prior to the onset of amyotrophic lateral sclerosis (ALS) are reported. In each patient, the onset of ALS some 18 months later was clearly defined clinically and confirmed by subsequent EMG studies. These unique observations show that ALS commences at a defined time, and that there is early generalisation with an initial phase of rapid progression.

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.

Involvement of the external anal sphincter in amyotrophic lateral sclerosis

In amyotrophic lateral sclerosis the striated pelvic floor sphincter muscles are functionally uninvolved, and pathological studies have confirmed the relative resistance of the Onuf nucleus motor neurons. We have evaluated the external anal sphincter (EAS) muscle in 16 patients with ALS using single fiber EMG, and compared the results with the findings in the semimembranosus-semitendinosus (SM-ST) muscles that have innervation from the L-5, S-1, and S-2 segments. The results were compared with a group of controls matched for age and sex. None of the patients or controls had symptomatic sphincter involvement and none of the 4 women studied were parous. Eight patients with ALS showed an increased fiber density in the EAS; 6 had an abnormal neuromuscular jitter. In 1 there was fibrillation in the EAS. In the SM-ST muscle 11 patients showed an increased fiber density, and 7 had an abnormal neuromuscular jitter. In 3 patients with ALS in whom there were abnormal findings in the EAS the bulbocavernosus reflex and pudendal nerve evoked potentials were normal. Neurogenic change was more marked in the SM-ST than in the EAS muscle. These findings show that the EAS is not normal in ALS. However, the relative resistance of the EAS to ALS is sufficient to prevent incontinence, even in the longer-surviving older patients.

Decremental motor responses to repetitive nerve stimulation in ALS

Repetitive nerve stimulation (RNS) of the trapezius muscle at slow rates was performed on 192 patients with amyotrophic lateral sclerosis (ALS). Fifty-six patients (29%) showed classical neuromuscular decrement of 10-43% (mean 16.8%) while 44 patients (23%) had a borderline decrement of 5-9%. The trapezius was significantly more sensitive in revealing the defect than the distal hypothenar muscles. In 30 patients followed serially, the decremental response remained constant or increased with time. However, 25% of patients continued to show no decrement in spite of progression of disease. No statistical correlation was found between decrement and clinical severity, disease staging, or disease progression. The finding that at least 50% of ALS patients show some degree of decrement on RNS of the trapezius muscle suggests that functional alterations of the neuromuscular junction accompany this disease.

Multiple orofacial indices in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by significant speech and swallowing problems resulting from upper and lower motor neuron loss. Weakness is the primary ALS disease-related sign, and measures of muscle strength have revealed nonuniform patterns of muscle weakness in orofacial muscles. To a large extent, muscle strength measures in these studies have not been evaluated in terms of functional significance, and few researchers have addressed the relation between weakness and motor neuron loss. This study addressed whether multiple measures, including static isometric maximum voluntary contraction (MVC), a dynamic measure of the peak rate of change of force (PRCF), an upper motor neuron (UMN) index, and a functional disability score (FDS) might enhance understanding of speech dysfunction in ALS. Ten males diagnosed with sporadic ALS showing mild speech impairment and an equal number of matched controls were studied. Tongue MVC and PRCF were more impaired than those of the lip and jaw, irrespective of the time post onset and site of initial symptoms. Results also suggested that disproportionate tongue impairment may be related to UMN deficits. However, impairments in the rate of contraction did not appear to be related to UMN deficits. Tongue weakness and tongue and lower lip PRCF were related to the degree of speech severity, but none of the measures was related to speech intelligibility. The value of a functional outcome measure like speech intelligibility and its role in characterizing orofacial involvement in the early stages of ALS bulbar impairment are discussed.

Juvenile distal spinal muscular atrophy of upper extremities in Chinese males: a single fibre electromyographic study of arms and legs

Single fibre electromyography (SFEMG) was performed on six young Chinese males with distal spinal muscular atrophy of the upper extremities. Abnormal SFEMG findings of increased fibre density, jitter and blocking were recorded over both arms and legs in all patients, suggesting a more generalised disturbance than would appear clinically.

New insights in motor neuron disease

In motor neuron disease there is a characteristic pattern of nerve cell loss and degeneration of related pathways. In surviving anterior horn cells several morphologically distinct, but generally non-specific, intracytoplasmic inclusion bodies have been recognized. Recently accumulations of previously unrecognized ubiquitinated material have been described in surviving neurons, which cannot be demonstrated with routine histological methods. These changes appear unique to this disease, and provide a new insight into the underlying pathology that may help understand the pathogenesis of this intriguing disorder. In this article we review the new information on the clinical, toxicological and pathological features of the disease.

Motor unit estimates in the biceps-brachialis in amyotrophic lateral sclerosis

A newly developed technique for estimating the number of motor units in the biceps-brachialis muscles and for studying the innervation patterns of motor units in the same muscles has been applied to the study of 17 patients with amyotrophic lateral sclerosis (ALS). Although severe motor unit losses were seen in many ALS cases, in most there were clear indications of increases in innervation densities, linked potentials, and blocking. This technique provides a powerful new tool for quantitatively assessing the extent of motor unit losses and the accompanying changes in innervation patterns in ALS.

Preclinical and subclinical events in motor neuron disease

It is suggested that in motor neuron disease there is a long preclinical period of relative tolerance and compensation before presentation with apparently focal features. During this phase the disease becomes disseminated through the motor system. The mode of acquisition of the disease, its relation to a possible genetic factor, and the processes leading to tolerance, to latency or progression, to the relative involvement of upper and lower motor neurons, to involvement of spinocerebellar pathways, and to asymmetry are fundamental problems in understanding the disease.

Central motor conduction is abnormal in motor neuron disease

Conduction in the central motor pathways of the brain and spinal cord was studied in 12 patients with motor neuron disease. Six healthy volunteers served as controls. Transcutaneous electrical stimulation of the cortex, cervical cord, thoracic cord and conus medullaris was used to determine motor latencies to the biceps brachii, thenar eminence and tibialis anterior muscles. Prominent, and often asymmetrical, slowing of central motor conduction was demonstrated in seven of the 12 patients; these findings were most marked in the spinal cord and in most cases correlated with clinical features of corticospinal involvement. In general it was more difficult to excite motor pathways in the central nervous system in the patients with motor neuron disease than in control subjects. Evidence of subclinical involvement of central motor pathways was found in five patients. The central lesion in motor neuron disease may thus contribute more significantly to the clinical deficit than has been realised, since the clinical signs of the upper motor neuron lesion are often masked by the more obvious lower motor neuron features.

Inhibition of terminal axonal sprouting by serum from patients with amyotrophic lateral sclerosis

To investigate the pathogenesis of amyotrophic lateral sclerosis, we compared the effect of serum from patients with this disease on the regenerative sprouting of terminal axons in botulinum-treated mouse gluteus muscle with the effects of serum from controls and from patients with diabetic peripheral neuropathy. Serum from 9 of 19 patients with the sporadic form of amyotrophic lateral sclerosis and from 2 of 6 patients with the familial form caused a reduction in the proportion of sprouting terminal axons, as compared with that found in muscles treated with serum from controls or diabetic patients. Immunoglobulin from patients with amyotrophic lateral sclerosis, when tested on immunoblots, recognized a 56-kilodalton protein secreted by denervated rat diaphragm muscle; rabbit antiserum raised against this protein also suppressed terminal axonal sprouting. Thus, we have detected an antibody in the serum of patients with amyotrophic lateral sclerosis that inhibits sprouting of neurons and subsequent reinnervation of skeletal muscle. Whether this antibody is of primary pathogenic importance or represents a secondary response to neuromuscular destruction is not known. In either case, serum from patients with amyotrophic lateral sclerosis may provide reagents for studies of the trophic communications between muscle and motor neurons.

A comparison of concentric needle electromyography, quantitative EMG and single fibre EMG in the diagnosis of neuromuscular diseases

Conventional concentric needle electromyography, quantitative electromyography using automatic analysis (Quant-EMG) and single fibre electromyography (SFEMG) were compared in the right biceps muscle of 10 patients with anterior horn cell disease and 20 patients with primary muscle disease. Abnormalities were demonstrable by all 3 techniques in the majority of cases irrespective of whether the biceps was weak. SFEMG was found to be more sensitive than Quant-EMG in neurogenic cases and it also provided an indication of disease activity. In cases of myopathy Quant-EMG was of more diagnostic help and was easier to perform than SFEMG. Large amplitude potentials found in some cases of myopathy were associated with increase in the mean amplitude on Quant-EMG and these probably emanate from hypertrophied muscle fibres.

Suppression of sprouting at the neuromuscular junction by immune sera

Injury of afferent motor axons or pathological loss of motoneurones from the spinal cord causes the remaining axons within a muscle to sprout and to reinnervate the denervated muscle fibres. Sprouting occurs at two sites along intramuscular axons, at nodes of Ranvier (nodal sprouting) and at the neuromuscular junction (terminal sprouting). Terminal sprouting is also produced by treatment with botulinum toxin and by other agents that render muscle inactive. The muscle probably provides a signal for terminal sprouting as restoration of muscle activity by direct electrical stimulation prevents sprouting. Such a signal might be a local change on the muscle fibre surface or a 'soluble' sprouting factor, although the failure to induce terminal sprouting in one muscle by denervating adjacent muscles argues against the latter hypothesis. I now report that rabbit antisera against a 56,000 (56K)-molecular weight protein secreted by denervated rat muscle suppress botulinum toxin-induced terminal sprouting in the mouse gluteus muscle. An immune response against this protein has also been detected in serum of patients with amyotrophic lateral sclerosis (ALS), a disease in which loss of motoneurones from the spinal cord is not accompanied by the degree of sprouting and reinnervation seen in other motoneurone diseases.

A longitudinal study of changes in motor units in motor neuron disease

In a longitudinal investigation of 14 patients with motor neuron disease motor units were studied in the biceps and first dorsal interosseous muscles in both arms, using single fibre EMG. The fibre density usually increased initially and this was occasionally accompanied by temporary improvement in strength. Later, as the fibre density decreased, increasing weakness and atrophy developed. The fibre density was rarely as high at any stage of the disease as in other chronic neurogenic disorders. Marked asymmetry was observed in individual patients at all stages of the disease.