Cervical paraspinal spontaneous activity in asymptomatic subjects

Paraspinal fibrillation potentials or positive sharp waves (PSWs) reportedly may be the only electrodiagnostic abnormality in patients with radiculopathies. However, spontaneous activity may be present in muscles of asymptomatic subjects. To determine whether abnormal spontaneous activity in the cervical paraspinal muscles is clinically relevant, we evaluated the prevalence of such activity in asymptomatic individuals and examined its relationship with age. Sixty-six asymptomatic subjects underwent a needle electromyographic examination of the paraspinal muscles bilaterally at the C5/6 and C6/7 levels. All of the recorded potentials were captured and their firing rates and waveforms were evaluated. The potentials were considered to be abnormal if reproducible trains of PSWs or fibrillation potentials were present. Eight of the 66 (12%) subjects showed PSWs, five bilaterally; none showed fibrillation potentials. A statistical analysis for the effect of age could not be performed due to the small sample size. Because electromyographic cervical paraspinal abnormalities can be found in asymptomatic subjects, caution should be exercised when attributing the etiology of neck pain to radiculopathy if the only electrodiagnostic findings are electromyographic cervical paraspinal abnormalities.     

An electrophysiological study of the deep peroneal sensory nerve

The electrodiagnosis of peripheral neuropathy is often based on nerve conduction abnormalities in sensory nerves of the lower extremities. We performed nerve conduction studies of the deep peroneal sensory nerve prospectively in 63 limbs of 38 normal subjects. The sensory amplitudes showed a decreasing trend with increasing age. 21% of subjects had absent sensory potentials, especially those in the older age groups. This was seen in contrast with superficial peroneal and sural potentials, which were universally present. Although the deep peroneal sensory nerve is located in the distal lower limb, it should be used with caution in evaluating peripheral neuropathy, in view of the frequent occurrence of absent potentials even in asymptomatic normal subjects.     

Aging of phrenic nerve conduction in the elderly.

OBJECTIVE: We elucidated the possible relationship between age and conduction parameters of phrenic nerve in subjects above the sixth decade, comparing with the data from middle-age controls. METHODS: Diaphragmatic action potentials (DAPs) were recorded on bilateral hemithoraces of 41 volunteers aged 60-101 years (old group) and 25 volunteers aged 35-55 years (middle-age group). Statistical analyses were performed to assess the effects of aging on latency, latency corrected by size (Lat/Dist), amplitude, and the right-left difference of these DAP parameters. RESULTS: In all 61 subjects, age showed a significant quadratic correlation with latency and with Lat/Dist, and a linear correlation with amplitude. The right-left differences ranged from 0.0 to 14.5% for latency and from 6.5 to 112.4% for amplitude in the elderly. CONCLUSIONS: The normal ranges of DAP parameters should be determined according to age. The left-right difference may be a useful reference in diagnosing unilateral phrenic nerve lesion. SIGNIFICANCE: The precise normal ranges of phrenic nerve conduction parameters presented will encourage investigations of neuropathies in subjects aged above 60.     

Fibrillation potential amplitude and muscle atrophy following peripheral nerve injury

Maximum peak-to-peak fibrillation potential amplitude was measured in 69 subjects between 7 days and 10 1/2 years post complete or partial peripheral nerve injury. Mean amplitude during the first 2 months was 612 muV; third and fourth months 512 muV, fifth and sixth months 320 muV. After the first year, no population of fibrillation potentials greater than 100 muV was recorded. The sciatic nerve was sectioned in 13 guinea pigs and animals studied up to 17 weeks. Fibrillation potential amplitude in gastrocnemius muscles declined paralleling that in humans. By the end of the study, type I fibers had lost almost half of their initial diameter and type II fibers had atrophied more than twice this amount. Fibrillation potential amplitude may be useful in estimating the time post nerve injury and appears to correlate with the surface area and fiber diameter of a type I muscle fiber.     

Methods for estimating numbers of motor units in biceps-brachialis muscles and losses of motor units with aging

This paper presents a new method, here applied to the biceps-brachialis muscles, for estimating motor unit numbers in healthy subjects. This method combines isometric contraction, intramuscular needle electrode recordings, and spike-triggered averaging techniques to measure the sizes of motor unit potentials as recorded in the innervation zone with surface electrodes. The number of motor units is then estimated by division of the maximum biceps-brachialis "M" potential recorded with the same surface electrodes and evoked by supramaximal stimulation of the musculocutaneous nerve, by the mean of at least 10 surface-recorded motor unit potentials. The requisite intramuscular recordings provide additional information as to innervation density, incidence of linked potentials, and impulse blocking, phenomena that are particularly common in neurogenic and myogenic disorders. There was clear evidence of losses of motor units in older subjects: subjects over 60 years of age having approximately half the numbers of motor units of subjects under 60 years of age.     

Electrophysiological studies in diabetic neuropathy

In 30 patients with diabetic neuropathy sensory potentials in the median nerve, motor conduction in the lateral popliteal and median nerves, and electromyographic findings in distal and proximal muscles were compared with the severity of symptoms and signs. All patients had abnormalities in at least one of the electrophysiological parameters. The sensory potentials were the most sensitive indicator of subclinical involvement; abnormalities were found in 24 patients, 12 of whom had no sensory symptoms or signs and five of whom had no other clinical or electrophysiological evidence of neuropathy in the upper extremities. This indicates that sensory nerve fibres may be affected before motor. The next most sensitive parameter was the presence of fibrillation potentials, found in more than half the distal muscles examined. Slowing in motor conduction in the lateral popliteal nerve was the only electrophysiological change correlated to the severity of the neuropathy, and no other electrophysiological parameter was correlated to the duration or the severity of the neuropathy or the diabetes. An onset of neuropathy before or simultaneously with the manifestations of the diabetes, as well as the frequent occurrence of asymptomatic changes in sensory conduction, support the evidence at hand that the neuropathy develops concomitantly with and as an integral part of the metabolic disturbance rather than as a consequence of the vascular complications of diabetes. Of three patients with clinical signs or symptoms of a diabetic amyotrophy, two had asymptomatic electrophysiological abnormalities in distal nerves and muscles, consistent with widespread involvement of the peripheral nerves. The third patient had electromyographic changes in the medial vastus muscles suggestive of a myopathy. Motor and sensory conduction in distal and proximal nerves were normal.     

Utility of ultrasound-guided surface electrode placement in lateral femoral cutaneous nerve conduction studies

Introduction: Meralgia paresthetica is a common clinical complaint for which some patients ultimately undergo surgical treatment. The lateral femoral cutaneous nerve (LFCN) has been difficult to reliably test electrophysiologically, likely due to anatomic variability and lack of responses in asymptomatic obese subjects. Methods: We compared a novel ultrasound‐guided antidromic sensory nerve conduction study (NCS) with a technique described previously in a population of normal subjects, of whom 50% had body mass indices within the obese range (>27.5). Results: Responses were obtained in at least 92% of subjects using either technique, and 92% of normal subjects had <60% interside variability using the ultrasound‐guided technique. Conclusions: LFCN sensory nerve action potentials can be obtained in the vast majority of normal subjects, even in an obese population and can provide a useful sensory NCS for evaluation of mid‐lumbar radiculopathy, plexopathy, or meralgia paresthetica. Muscle Nerve, 2011     

Proximal and segmental motor nerve conduction in the sciatic nerve produced by percutaneous high voltage electrical stimulation

Percutaneous high voltage electrical stimulation was applied to the proximal sciatic nerve at the hip in 18 normal subjects to evaluate motor conduction in the proximal sciatic nerve, and short-segment stimulation of the sciatic and posterior tibial nerves was given in 6 normal subjects. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis (AH) and extensor digitorum brevis (EDB) muscles. Supramaximal stimulation was easily obtained at the proximal sciatic nerve and all the sites in the short-segment stimulation. The motor nerve conduction velocity of the sciatic nerve between the hip and the popliteal fossa was 49.2 ± 4.24 m/sec in the tibial division and 54.1 ± 6.48 m/sec in the peroneal division. The respective peak-to-peak amplitude and negative-peak areas of the CMAPs at the hip were reduced to 86.8 ± 5.65% and 97.3 ± 5.36% for the tibial division, and 93.4 ± 7.06% and 96.8 ± 5.09% for the peroneal division as compared to the values for the popliteal fossa. The negative-peak duration of the CMAPs at the hip point were increased to 109.2 ± 7.2% for the tibial nerve and 107.1 ± 5.68% for the peroneal nerve as compared with the duration at the popliteal fossa. This method is non-invasive and useful for evaluating motor nerve conduction in the lower limb.     

Electrophysiological studies in the assessment of polyneuropathies

In many cases, one encounters great difficulties in finding causes of polyneuropathies among some 100 etiologies. However, in current practice, the diagnostic span is not so large. At this point, it is usual to get some aid from electrophysiologic tests in order to determine the nature of the peripheral nerve disorder. Examination with needle electrodes is mainly useful to detect fibrillation potentials or positive sharp waves which are indicative of an acute or subacute axonal neuropathy in which the process of degeneration is more important than the capacities of regeneration. Studies of sensory and motor nerve conduction velocities is of a more important utility to separate the different types of peripheral neuropathies: axonopathies in which nerve conduction velocities are normal or slightly decreased but in which muscular evoked potentials and sensory potentials are reduced, myelin disorders in which nerve conduction velocities are markedly decreased and in which finding of conduction blocks allows to individualize two forms, motor and sensory neuronopathies, where the pure lesion of the motor or sensory cell bodies correlate with the normality of sensory and motor pathways respectively.     

Denervation in hemiplegic muscles

This study examined the frequency of denervation activity in hemiplegic muscles in relation to the size and location of the central lesion. We studied 20 patients, 14 with major unilateral cerebral infarctions in the middle cerebral or internal carotid territories; four with a single lacune in the pons, internal capsule, or thalamus; and two with precentral infarcts. Using somatosensory evoked potentials, motor conduction studies, and assessments of conduction across the plexus and roots, we detected no conduction abnormalities on the affected side. Fibrillation was common in both groups, especially in distal and intermediate muscles. The distribution of the fibrillation and the normal conduction studies suggested that trauma of peripheral nerves was not a factor. Although the normal conduction studies and pattern of fibrillation activity do not exclude peripheral nerve trauma as the cause of the fibrillation, we suggest that transsynaptic degeneration is a reasonable alternative explanation.     

Examination of central and peripheral motor pathways by standardized magnetic stimulation

A standardized magnetic stimulation procedure for evaluation of central and peripheral motor pathways is described together with the results of motor evoked potential (MEP) recordings from 6 muscles in 50 healthy volunteers aged 18 to 60 years. Facilitation of the neuronal pathways was standardized using the integrated electric activity of the EMG as a gauge. The target muscles were: the brachial biceps (BB), the radial carpal flexor (FCR), the first dorsal interosseus of the hand (FDI), the medial vastus of the quadriceps muscle (VM), the anterior tibial (TA) and the abductor hallucis muscles (AH). The parameters used were the conduction times and the amplitudes of the CMAPs evoked by brain and root stimulation. CMAPs could be recorded from all muscles in all but three subjects in whom cortical stimulation was unsuccessful in one TA and two AHs, while root stimulation was negative in two TAs and one AH. Height and conduction times were significantly correlated, while age and conduction times were not. By linear regression 30-60% of the variation in the conduction times could be explained by the variation in height. The residual variation of the conduction times was less than in most other non-standardized studies and comparable to peripheral electrical motor conduction studies.     

Estimates of functional motor axon loss in diabetics

Estimates of the number of motor units in extensor digitorum brevis (EDB) and in the thenar muscles were made electrophysiologically in a group of 66 diabetic subjects. Loss of motor units was common in those with no clinical evidence of neuropathy and was most severe in EDB. The clinical form of the neuropathy was a poor guide to the severity of EDB or thenar motor unit loss. Motor unit losses in diabetics 60 years of age or over did not differ from those found in many control subjects of equivalent age.The finding of motor unit loss, abnormal digital sensory potentials and motor conduction velocity slowing in diabetics without a neuropathy and in unaffected limbs of those with a neuropathy, pointed to a general metabolic disturbance of diabetic peripheral nerves. This may have made diabetic nerves more liable to nerve entrapment and probably accounted for the large number of subjects with local neuropathies, particularly of the median nerve in the region of the carpal tunnel.     

Issues & opinions: Are fibrillation potentials and positive sharp waves the same? No

Electrodiagnostic medicine consultants report electrical activity in muscle recorded at rest and during voluntary movement by means of waveform and firing rate characteristics. This principle allows us to distinguish fibrillation potentials from positive sharp waves. Although in most cases these two potentials have the same clinical significance, there are at least five different situations in which they do not have an identical meaning: (1) positive sharp waves can be recorded earlier after a peripheral nerve injury than can fibrillation potentials; (2) occasionally, nonclinically significant diffuse positive sharp wave activity may be seen in the absence of fibrillation activity (i.e., “EMG disease”); (3) positive sharp waves may be seen in distal muscles of “normal” subjects without the presence of fibrillation activity or clinical significance; (4) positive sharp waves without fibrillation potentials may be seen following local muscle trauma; and (5) positive sharp waves may be seen alone in some demyelinating polyneuropathies. By accurately describing the observed potentials, the electrodiagnostic medicine consultant may be able to obtain more clinically useful information from an electrodiagnostic study. © 1996 John Wiley & Sons, Inc.     

Juvenile progressive bulbar palsy. Clinical and electrodiagnostic findings

Differentiation of juvenile progressive bulbar palsy from bulbar myasthenia gravis is difficult. Characteristics of both may include ocular involvement, fluctuant course, abnormal fatigability, and normal acetylcholine receptor (AChR) antibody titers. Electrodiagnostic evaluation may demonstrate moment-to-moment variability in motor unit action potential amplitude, fibrillation potentials, and decremental motor evoked responses. Increased jitter with blocking may be the most prominent electrodiagnostic abnormality in either disorder, even in asymptomatic extremity muscles. Complete paralysis of facial muscles with electrical silence on needle electromyography, low-amplitude facial evoked responses without a decrement to repetitive stimulation, increased jitter and fiber density in asymptomatic extremity muscles, and normal AChR antibody levels suggested juvenile progressive bulbar palsy in two patients initially thought to have bulbar myasthenia. Early differentiation of these disorders is important because of therapeutic, genetic, and prognostic implications.     

Clinical electrophysiological characterization of the acquired neuromyotonia phenotype of autoimmune peripheral nerve hyperexcitability

Acquired autoimmune neuromyotonia is regarded as part of the spectrum of peripheral nerve hyperexcitability disorders. We aimed to use clinical neurophysiological measurements to study the extent, distribution, and characteristics of spontaneous motor unit potentials in 11 patients with acquired neuromyotonia. Investigations revealed that most spontaneous discharges recorded were motor unit, or partial motor unit potentials of normal size. Bursts of motor unit potentials arose more commonly from distal portions of the peripheral nerve and had abnormal absolute and relative refractory periods. Spontaneous discharges in some patients occurred in semirhythmic bursts in certain muscles. No patient had neurophysiological abnormalities detectable in first-order neurons of the central nervous system when using transcranial magnetic stimulation to estimate the threshold for corticomotor excitation and determine central motor conduction time. Only patients with coexistent myasthenia gravis had neurophysiologically detectable defects in neuromuscular transmission. The pathogenic region of abnormality in peripheral nerve hyperexcitability disorders therefore seems to lie within the terminal branches of peripheral motor nerves.     

Trigeminal motor nerve conduction: Deep temporal and mylohyoid nerves

This article describes nerve conduction studies of the deep temporal nerve (DTN) and the mylohyoid nerve (MHN) motor branches of the trigeminal nerve. These nerves were stimulated intraorally with a pediatric surface stimulator. Compound muscle action potentials were recorded over the temporalis and mylohyoid muscles with surface electrodes. Forty-two subjects were studied. In all subjects the MHN response was elicited bilaterally, giving an upper latency limit of 2.3 ms. The mean MHN amplitude was 4.9 mV (SD = 1.8 mV, minimum = 1.3 mV). The maximal side-to-side latency difference was 0.4 ms, and the maximal side-to-side amplitude difference was 2.2 mV. The DTN response was only elicited bilaterally in 25 (60%) subjects. The average DTN latency was 2.1 ms (SD = 0.3, maximum = 2.7 ms). The average DTN amplitude was 4.3 mV (SD = 2.0, minimum = 0.3 mV). The MHN responses were the least technically demanding, and were more consistently elicited than the DTN responses. These nerve conduction techniques should prove useful in patients with trigeminal nerve disorders. © 1996 John Wiley & Sons, Inc.     

Evoked potentials in HIV infection]

The study of the literature data on the multimodal evoked potentials in HIV infected patients shows many abnormalities as well in asymptomatic subjects without AIDS as in AIDS subjects with or without neurological signs. Visual evoked potentials (VEPs) reveal prolonged P100 wave latency in 22% of HIV asymptomatic subjects and in 26% of HIV symptomatic subjects; brainstem auditory evoked potentials (BAEPs) reveal an increase of the interpeak latency I-V in 16% of asymptomatic subjects and in 32% of symptomatic subjects; somatosensory evoked potentials (SEPs) by median nerve stimulation reveal prolonged central conduction time in 6% of asymptomatic subjects and in 11% of symptomatic subjects; somatosensory evoked potentials (SEPs) by tibial nerve stimulation reveal prolonged central conduction time in 4% of asymptomatic subjects and in 45% of symptomatic subjects; motor evoked potentials (MEPs) by magnetic stimulation reveal prolonged central motor conduction time in 46% of asymptomatic subjects.     

Spinal evoked potentials in normal Japanese infants and children

The spinal evoked potentials on right peroneal nerve stimulation were recorded with surface electrodes in 58 normal children of 41 weeks to 15 years old. Bipolar recordings were performed. In all subjects, tri- or quadri -phasic potentials with poorly defined initial positive phases were recorded. The latency of the evoked potentials increased progressively from the lumbar to cervical location. The peripheral conduction velocity from the stimulating cathode in the popliteal fossa to the lumbar recording location increased until 4 or 5 years, and then reached a plateau. Spinal conduction velocity between the lumbar and cervical locations increased until 7 years, and then remained constant.     

Analysis of motor conduction velocity in the human median nerve by computer simulation of compound muscle action potentials.

A digital computer was used to reconstruct compound muscle action potentials recorded from the human thenar eminence after stimulation of the median nerve. The programme allowed the following parameters to be varied: (1) the dimensions of a representative single motor unit potential; (2) the number of motor units in the muscle and the range and distribution of conduction velocities in their nerve fibres; and (3) the distance along the nerve from the point of stimulation to the muscle. The reconstructed compound muscle action potentials were similar to real compound potentials recorded from normal subjects. The number of single motor units and the range of conduction velocities required for the reconstruction correlated with quantitative histologic studies of the recurrent branch of the median nerve to the thenar muscles. By altering the distribution of conduction velocities it was possible to study the effect of abnormal patterns of nerve conduction on the configuration of the simulated compound muscle action potentials. It was found that abnormally slow conduction caused an increased discrepancy between the main parameters of compound potentials corresponding to stimulation of the nerve at proximal and distal sites. These observations suggest that a careful analysis of the differences between pairs of compound muscle action potentials may provide a method for more detailed assessment of conduction velocity in clinical studies of peripheral nerve disorders.     

Neurophysiological changes in neurologically asymptomatic hypothyroid patients: a prospective cohort study.

This is a prospective cohort study on neurologically asymptomatic patients with primary hypothyroidism. It was conducted to evaluate the frequency and pattern of neurophysiological changes in this group of patients. Twenty-three subjects were included over a period of 2(1/2) years. Neurophysiological evaluation included nerve conduction studies (NCS) of median, ulnar, and peroneal motor nerves as well as median palmar and ulnar and sural sensory responses. Electromyography of deltoid, first dorsal interosseous, vastus lateralis, and tibialis anterior muscles was performed with concentric needle electrodes in which duration, amplitude, and stability of motor unit action potentials, recruitment, and interference pattern were evaluated. NCS showed that 52% of the patients had some abnormality, predominantly of the motor demyelinating pattern, as evidenced by prolonged F-wave and distal latencies with normal amplitudes in most affected nerves. Thirty percent of patients had median mononeuropathy consistent with carpal tunnel syndrome. Nondisfigurative myopathic changes in the form of myopathic motor unit action potentials without spontaneous activity were seen in 74% of the patients, most commonly in deltoid (70%). Frequencies of involvement of other muscles were 39% in the vastus lateralis muscle, 26% in tibialis anterior muscle, and 9% in the first dorsal interosseous muscle. We conclude that electromyographic/NCS changes commonly exist in treated, neurologically asymptomatic patients with hypothyroidism and are most frequently myopathic. Median neuropathy is the most common nerve abnormality. Other nerves are involved, with a higher tendency for motor nerve demyelination. We speculate that some neuromuscular changes secondary to hypothyroidism persist after treatment and that motor nerve abnormalities are less likely to be symptomatic than sensory nerve changes in these patients.