Reflex effects of vibration in patients with spinal cord lesions.

The vibration reflex was studied in 49 patients with traumatic spinal cord lesions. It was elicited in all patients, even after presumably complete division of the cord. The vibration relfex consisted of a short-latency, brief outburst of phasic activity of motor units, followed by rapidly decreasing phasic component and a later slowly declining tonic component. When periods of vibration were repeated at short intervals of 2 to 10 seconds, the responses showed an approximately exponential decline, although the beginning of each subsequent response was always larger than the end of the preceding response. A large part of this decline can be characterized as a habituation of the vibration reflex. In comparison with the vibration reflex in normal subjects, the phasic component was increased and the tonic one reduced. The tonic component was especially susceptible to potentiation and dishabituation by voluntary effort to contract the vibrated muscle, even in some patients with no other evidence that the lesion was incomplete. We suggest that the tonic component of the human vibration reflex depends, at least in part, on segmental interneurons and their descending spinal pathways, while the phasic component depends mainly on the excitability level of spinal motoneurons.

Multiple sclerosis and myasthenia gravis. A case report with single fiber electromyography.

A 34-year-old woman with long-standing multiple sclerosis had a 2-year history and physical signs of myasthenia gravis. The edrophonium chloride (Tensilon) test was positive. Repetitive stimulation of the ulnar nerve at 3 Hz did not show evidence of myasthenic response; however, a single-fiber electromyography demonstrated evidence of neuromuscular block as seen in myasthenia gravis, which was reversed to normal after intravenously administered edrophonium. The patient improved on anticholinesterase medication. It is suggested that patients with multiple sclerosis who have unusual features such as in the patient reported here should be investigated for the presence of myasthenia gravis to ensure proper treatment.

Flexion withdrawal reflex as recorded from single human biceps femoris motor neurones.

Reflex responses were elicited in the biceps femoris muscle of patients with cervical spinal cord lesions by stimulating the sural nerve and recording from single motor neurones by single fibre EMG technique. The consecutive responses within the surface-recorded early component displayed a latency jitter between 500 and 600 microsec (S.D.), suggesting an oligosynaptic reflex arc. These responses were rarely seen; they were suppressed by increasing the stimulus strength. The surface-recorded late component consisted in the single fibre EMG recordings of repetitive discharges of individual motor neurones. The latency jitter of the earliest of these discharges was about 1440 microsec, and it progressively increased in the later discharges, reflecting increasingly more variable central conduction time. Ischaemia of the leg made some of the late discharges at a latency of about 0.5 sec remarkably stable and reduced their jitter. They may represent responses to the activity of slowly conducting afferent fibres, normally suppressed by inflow along the fast conducting fibres. Stimulation of dorsal columns through epidurally placed electrodes at T1 and T2 levels resulted in a complete suppression of repetitive discharges, outlasting the actual stimulation. TENS and light stroking of the skin below the level of the spinal cord lesion, as well as subthreshold stimuli to the sural nerve, had a similar effect. These results suggest that the late component of the flexion reflex may share some of the neural mechanisms responsible for feeling pain.

The study of normal and abnormal neuromuscular transmission with single fibre electromyography.

The use of single fibre electromyography (SFEMG) in the study of neuromuscular transmission across individual motor endplates in situ is reviewed. The neuromuscular jitter can be studied both during voluntary contraction and electrical activation of the muscle fibre. The differences, pitfalls and advantages of these methods are discussed. Findings in myasthenia gravis and other disorders of the neuromuscular transmission are examined.

Percutaneous stimulation of human corticospinal tract: a single-fibre EMG study of individual motor unit responses.

The technique of electrical stimulation of the brain through intact scalp was applied to activate the corticospinal tract (CST) of healthy human volunteers. Single motoneurone responses were picked up by a special (single fibre EMG) needle electrode. Our finding of relatively small latency variation of consecutive single motor unit responses seems to support the concept of predominantly monosynaptic transmission at the spinal level. The alternation between several discrete latencies seems to reflect a complexly shaped spinal motoneurone excitatory postsynaptic potential (EPSP), which could be due to either alternating direct/indirect (via other cerebral neurones) activation of the corticospinal tract (CST) neurones, or alternating mono- or oligosynaptic transmission at the spinal level, or multiple CST impulses in response to a single stimulus.

Single fibre electromyography in various processes affecting the anterior horn cell.

SFEMG recordings were carried out in patients with amyotrophic lateral sclerosis, progressive muscular atrophy, familial spinal muscular atrophy and syringomyelia. The fibre density was increased in all conditions, especially in progressive muscular atrophy indicating marked collateral sprouting. The duration of the action potential was increased indicating a mixture of hypertrophic and atrophic fibres and slowly conducting newly formed nerve sprouts. The action potentials were unstable with varying degree of impulse blocking especially in the more progressive cases (ALS), representing recent re-innervation. The SFEMG method is used to characterize the functional status of the motor unit and helps in diagnosis and in predicting prognosis. In addition, SFEMG recordings reveal abnormalities in clinically and electromyographically normal muscles.

Brainstem auditory evoked potential (BAEP) abnormalities in brucellosis.

Twelve patients with neurobrucellosis and 17 patients with systemic brucellosis without neurological involvement underwent a brainstem auditory evoked potentials (BAEP) study. All neurobrucellosis patients (100%) showed abnormalities in their BAEP recordings, suggestive of brainstem lesions at various levels. On the other hand, only 5 (29%) of the 17 patients with systemic brucellosis had mild unilateral BAEP abnormalities, while the remaining 12 had normal responses. Comparison of pooled data between the systemic brucellosis and neurobrucellosis groups showed highly significant differences in all BAEP parameters. The recording of BAEP is thus considered a sensitive supplementary method to reveal CNS lesions in patients with neurobrucellosis.

Brainstem auditory evoked potentials in Wilson's disease.

Twelve patients with Wilson's disease, aged 11-25 years, underwent brainstem auditory evoked potential (BAEP) study. The results were correlated to clinical, neuroradiological and laboratory data. Ten had prominent to severe neurological manifestations, suggestive of involvement of one or several CNS structures, and 2 were neurologically free. All had evidence of abnormal copper metabolism, and 8 had CT scan evidence of brain atrophy, or hypodense areas in basal ganglia, or both. The 2 patients without neurological manifestations as well as one with neurological signs had normal BAEP. One patient with neurological signs had increased N1 latency due to cochlear hearing loss, but normal interpeak intervals, while 8 of 10 patients with prominent neurological symptoms and signs had abnormal BAEPs (prolongation of NIII-NV interpeak interval). The value of NIII-NV interpeak interval correlated with the number of different neurological signs (neurological score) attributable to involvement of different CNS structures (r = 0.64 at P = 0.001). Abnormal BAEPs do not seem to be an early finding in Wilson's disease.

Electrical microstimulation with single-fiber electromyography: a useful method to study the physiology of the motor unit.

This article reviews the essential technical principles and findings with electrical microstimulation as used in conjunction with single-fiber electromyography (SFEMG). It highlights the details in the microphysiology of the motor unit that can be conveniently studied with these methods, particularly the neuromuscular transmission at the individual motor endplates, muscle fiber recovery functions, and a variety of late responses. The differences, advantages, and disadvantages of the stimulation method of jitter measurement, compared to the original method, in the voluntarily activated muscle are described. Special attention is given to the pitfalls of the technique. Indications for clinical use of stimulation SFEMG in the electromyography laboratory are suggested.

Segmental neurophysiological mechanisms in scoliosis.

Segmental spinal reflexes (stretch reflexes) were studied in patients with scoliosis. The proprioceptive responses to the phasic stretch of the paraspinal muscles were asymmetric in all patients, and were increased on the convex side. The asymmetry was more pronounced when the patients were standing. The observed asymmetry of the reflex responses was taken to indicate asymmetry in the tone and postural activity of the superficial layer of the paraspinal muscles. A reciprocal relationship was found in the segmental reflex organisation between the superficial and deep layers of the paraspinal muscles. The increase in reflex response of the superficial muscles on the convex side can be due to diminished reciprocal inhibition from weak, deep muscles. Thus a segmental neurogenic disorder involving predominantly the deep paraspinal muscles of the convexity of the curve may be the primary lesion responsible for the development of scoliosis.

Single fiber electromyography in studies of neuromuscular function.

Single-fiber electromyography (SFEMG) allows precise study of the microphysiology of the human motor unit under normal conditions. The physiological parameters that can be quantified include impulse transmission along the intramuscular axon collaterals, pre- and post synaptic events at the neuromuscular junction, and muscle fiber membrane properties. This chapter illustrates some of the advantages of SFEMG in studies of neuromuscular fatigue in normal muscle, as well as in disorders of neuromuscular transmission, and conditions associated with disturbed muscle fiber depolarization-repolarization.

Muscle fiber conduction velocity changes with length.

While recording activity from individual muscle fibers by single fiber EMG (SFEMG), stimulated either through their axons or directly, the length of the recorded muscle fiber was changed--stretched or made shorter--by manipulating the recording needle or by passive joint movements. This resulted in significant changes of latency corresponding to an increase in propagation velocity on shortening of the muscle fiber and to a slowing of its lengthening. The maximum increase in velocity was estimated to 33% and slowing to about 22%. These length-dependent changes of muscle fiber propagation velocity are suggested to contribute to the supernormal phase of propagation velocity recovery function and to be responsible for an important part of the myogenic, interdischarge interval-dependent, jitter.

A study of the H-reflex by single fibre EMG.

The latency of consecutive H-reflex responses of single human triceps surae motoneurones varies up to 2,500 µs. A large part of this variation was shown to occur at the synaptic transmission. A moderate increase in stimulus strength from the threshold value shortened the mean latency and reduced the latency variation, presumably as a result of spatial summation of excitatory inputs. Further increase to maximum strength lengthened the mean latency, increased the variation, and resulted in a dropping out of some responses which was not produced by collision by antidromic impulses. These effects are believed to be due to an active inhibition. Changes of the latency were also obtained by Jendrassik's manoeuvre and facilitatory and inhibitory conditioning stimuli.

Multiple innervation of muscle fibers in myasthenia gravis.

Single fiber EMG recordings from patients with myasthenia gravis obtained during axonal microstimulation revealed an occasional bimodal distribution of response latencies. This phenomenon could be dependent on stimulus strength, however, in a way different from that in the axon reflex. It is suggested to be due to dual neuromuscular junctions (NMJs) supplied by two different motor neurons. Some cases of bimodal jitter were not dependent on stimulus strength and are assumed to be due to dual innervation by the same neuron. The phenomenon could only be demonstrated at abnormal NMJs with partial impulse blocking. It is suggested to reflect multiple reinnervation of muscle fibers that had undergone functional or structural denervation in the course of the immune attack against the original NMJ. This study suggests that the coexisting NMJs from the same or different motor neurons may be functional at the same time.

Single fiber EMG in juvenile idiopathic scoliosis.

A single fiber EMG (SFEMG) study was performed in 51 patients with idiopathic juvenile scoliosis of moderate degree (mean 23.8 degrees of Cobb), aged 7-18 years (mean 13.2 years). The findings in the extensor digitorum communis muscle (EDC) include a moderate but significant increase in fiber density (mean 2.02, +/- 0.21, P less than 0.001), a mild but significant (P less than 0.001) neuromuscular transmission abnormality (7.6% of fibers showed increased jitter and 4.5% intermittent blocking), and a moderately prolonged mean interspike interval (mean 0.98 msec, +/- 0.20, P less than 0.005) in EDC. Five of the patients had normal fiber density, 9 had a normal jitter study, and further 7 had a normal mean interspike interval. However only one had all the parameters normal. The paraspinal and intercostal muscles at the apex of the scoliotic curvature examined in some of the patients showed similar abnormalities. The study thus suggests the existence of a subclinical systemic neuromuscular disorder in nearly all of our patients with idiopathic scoliosis, which might have a pathogenetic significance.