The investigation of traumatic lesions of the brachial plexus by electromyography and short latency somatosensory potentials evoked by stimulation of multiple peripheral nerves.

A study of 10 patients with brachial plexus trauma was performed to determine whether the diagnostic accuracy of sensory evoked potentials (SEPs) may be improved by using stimulation of multiple peripheral nerves (median, radial, musculocutaneous and ulnar). In addition, the relative advantages of SEPs and peripheral electrophysiological studies were considered. SEP patterns following most common brachial plexus lesions were predictable. Injuries to the upper trunk affected the musculocutaneous and radial SEPs predominantly. Lower trunk or medial cord lesions primarily affected ulnar SEPs. Diffuse brachial plexus lesions affected SEPs from all stimulation sites. In the majority of cases, the necessary information was obtainable from conventional EMG: however, for lesions involving the upper segments only, SEP techniques were more useful. It is suggested that selective SEPs from appropriate peripheral nerves when interpreted in combination with conventional EMG may add useful additional information.     

Interactions of somatosensory evoked potentials: simultaneous stimulation of two nerves.

To analyse the mechanism by which sensory inputs are integrated, interactions of somatosensory evoked potentials (SEPs) in response to simultaneous stimulation of two nerves were examined in 12 healthy subjects. Right, left and bilateral median nerves were stimulated in random order so that a precise comparison could be made among the SEPs. The arithmetical sum of the independent right and left median nerve SEPs was almost equal within 40 msec of stimulus onset to that evoked by the simultaneous stimulation of bilateral median nerves. However, a difference emerged after 40 msec. The greatest difference was recorded after 100 msec. Sensory information from right and left median nerves may interact in the late phase of sensory processing. Left median, left ulnar, and both nerves together were stimulated. The sum of the SEPs of left median and ulnar nerves was not equal to that evoked by the simultaneous stimulation of the two nerves even at early latencies. Differences between them were first recorded at 14-18 msec and became greater after 30-40 msec. It is suggested that the neural interactions between impulses in the median and ulnar nerves begin below the thalamic level.     

Short-latency somatosensory-evoked potentials from radial, median, ulnar, and peroneal nerve stimulation in the assessment of cervical spondylosis. Comparison with conventional electromyography

A study of data on 30 patients with cervical spondylosis was carried out to determine whether short-latency somatosensory-evoked responses (SEPs) to median, ulnar, radial, and peroneal nerve stimulation provided additional information to that obtained by electromyography (EMG), late responses, and peripheral conduction studies. Peripheral studies, EMG results and SEPs were within normal limits in ten patients with pain, but without objective neurological deficit. By contrast, of ten patients who had objective signs of root compression, conventional EMG results were normal in nine, but abnormalities of the SEPs from radial nerve stimulation were obtained in only five patients, and were normal from ulnar and median nerve stimulation. In ten patients with clinical features of myelopathy, seven had abnormal median SEPs and all had abnormal peroneal SEPs, whereas EMG results were abnormal in only five patients. It is suggested that SEPs and EMG are both of limited use in patients with only symptoms of root compression. In patients with signs of root compression, EMG is the most sensitive procedure; however, some additional information can be obtained from superficial radial SEPs. In patients with cervical myelopathy, SEP was the most useful procedure, especially when upper and lower limbs were studied.     

Segmental dysfunction of the cervical cord revealed by abnormalities of the spinal N13 potential in cervical spondylotic myelopathy.

We studied somatosensory potentials (SEPs) evoked by stimulation of radial, median, and ulnar nerves in 11 patients with MRI evidence of cervical spondylosis. All patients presented with progressive spastic paraparesis that was either isolated or associated with lower motor neuron signs in the upper limbs, with preserved joint, touch, pain, and temperature sensations in the four limbs. In all patients, scalp SEPs reflecting the activity of the dorsal column system up to the parietal cortex were normal while segmental cervical cord dysfunction was manifested by an abnormal spinal N13 potential in 95% of radial, 90% of median, and 54% of ulnar nerve SEPs. These subclinical abnormalities of the spinal N13 SEP probably result from reduced blood supply due to compression of the anterior spinal artery in patients with cervical spondylotic myelopathy.     

Somatosensory evoked potentials in chronic acquired demyelinating peripheral neuropathy

We recorded somatosensory evoked potentials (SEPs) over the scalp in eight patients with chronic acquired demyelinating peripheral neuropathy. They were obtained from 15 nerves in which sensory nerve action potentials (SNAPs) were absent or not more than 1 microV, but from which motor responses could be elicited. Motor and sensory (SEP-derived) conduction velocity was determined from the difference in response latency with wrist and elbow stimulation. In 11 nerves, afferent conduction velocity was slowed. In 10, there was relatively equal slowing in sensory and motor axons, whereas in 1 there was disproportionate slowing in afferent fibers. In four nerves, afferent conduction velocity was within the normal range despite slowing of motor conduction. We conclude that SEPs may be useful in evaluating peripheral sensory conduction in the absence of SNAPs, but can provide misleadingly normal data, presumably because of central amplification of an attenuated response arising from a few axons that conduct normally.     

Somatosensory evoked potentials after multisegmental upper limb stimulation in diagnosis of cervical spondylotic myelopathy.

Radial, median, and ulnar nerve somatosensory evoked potentials (SEPs) were recorded, with non-cephalic reference montage, in 38 patients with clinical signs of cervical myelopathy and MRI evidence of spondylotic compression of the cervical cord. Upper limb SEPs are useful in spondylotic myelopathy because SEPs were abnormal in all patients for at least one of the stimulated nerves and SEP abnormalities were bilateral in all patients but one. Reduction of the amplitude of the N13 potential indicating a segmental dysfunction of the cervical cord was the most frequent abnormality; it occurred in 93.4%, 84.2%, and 64.5% of radial, median, and ulnar nerve SEPs respectively. A second finding was that the P14 far-field potential was more sensitive than the cortical N20 potential to slowing of conduction in the dorsal column fibres. The high percentage of N13 abnormalities in the radial and median rather than in the ulnar nerve SEPs correlated well with the radiological compression level, mainly involving the C5-C6 vertebral segments. Therefore the recording of the N13 response is a reliable diagnostic tool in patients with cervical spondylotic myelopathy and P14 abnormalities, though less frequent, can be useful in assessing subclinical dorsal column dysfunction.     

Localization of sensory levels in traumatic quadriplegia by segmental somatosensory evoked potentials

We studied the usefulness of cortical somatosensory evoked potentials (SEPs) elicited by segmental sensory stimulation in traumatic quadriplegia. By stimulating sensory branches of musculocutaneous (C5, C6), median (C7, C8), and ulnar nerves (C8), we studied 10 chronic traumatic quadriplegics and compared them with age-matched controls. In all traumatic quadriplegics tested, the SEP abnormalities provided a direct linear relationship with clinical localization of posterior column sensory levels. Our findings suggest that segmental SEPs can enhance the clinical assessment of posterior column sensory levels in chronic traumatic quadriplegia. Further studies may find this technique useful in acute quadriplegia, particularly during surgical monitoring.     

Forearm ulnar-to-median nerve anastomosis of sensory axons

A 22-year-old man showed electrophysiological evidence of an ulnar-to-median nerve communication involving only sensory fibers. The nerve action potentials evoked by stimulation of the middle finger (ulnar side) and the ring finger (radial side) digital nerves were propagated with the median nerve at the wrist and the ulnar nerve at the elbow. He was the only subject among 30 studied with this abnormality.     

Sensory deficits of a nerve root lesion can be objectively documented by somatosensory evoked potentials elicited by painful infrared laser stimulations: a case study.

Somatosensory evoked potentials (SEPs) in response to painful laser stimuli were measured in a patient with a unilateral sensory deficit due to radiculopathy at cervical levels C7 and C8. Laser evoked potentials (LEPs) were compared with SEPs using standard electrical stimulation of median and ulnar nerves at the wrist and mechanical stimulation of the fingertips by means of a mechanical stimulator. Early and late ulnar and median nerve SEPs were normal. Mechanical stimulation resulted in w shaped early SEPs from all five fingertips with some degree of abnormality at the fourth and fifth digits of the affected hand. Late LEPs were completely absent for stimulations at affected dermatomes and normal in the unaffected control dermatomes. The border between skin areas with normal or absent LEPs was very sharp and fitted the dermatomes of intact C6 and damaged C7 and C8 nerve roots. It is suggested that pain dermatomes are narrower than tactile dermatomes because thin fibres of the nociceptive system, activated by laser stimuli, probably do not overlap between adjacent spinal segments to the same extent as thick fibres of the mechanoreceptive system, activated by standard electrical or mechanical stimulation.     

Assessment of peripheral nerve crush injury with cortical somatosensory evoked potentials in the cat

Somatosensory evoked potentials (SEPs) were recorded from anesthetized cats to assess regeneration of the superficial radial nerve after crush injury. SEPs were recorded by epidural electrodes chronically implanted over the primary somatosensory cortex (SI) and elicited by electrical stimulation of the dorsal surface of the contralateral forepaw. The stimulation intensity and impedances measured across the skin-stimulating electrodes were maintained constant for each animal throughout the experimental period. SEPs which disappeared after the radial nerve crush were elicited within the first week by stimulation applied to skin nearest the nerve crush site. Radial nerve crush also affected the SEP elicited by stimulating the intact ulnar side of the forepaw. In all animals examined, the SEP amplitude evoked by stimulation of the skin supplied by the ulnar nerve increased immediately after radial nerve crush. As early as 4 days after nerve crush, SEPs were elicited by stimulating the distal region of the digits that had been denervated. This phenomenon might be accounted for by peripheral collateral sprouting of intact neighboring nerves and/or by central unmasking of ulnar median input from the denervated radial skin area. Within 117 days, SEPs were elicited by stimulation applied anywhere in the previously denervated forepaw area. The topographical amplitude distribution of SEPs after reinnervation was not identical to that obtained under baseline conditions. The use of SEPs for chronic recording is an effective means to monitor reinnervation of skin after peripheral nerve injury.     

Mixed nerve action potentials in acquired demyelinating polyneuropathy

Uncertainty about motor and sensory contributions in abnormal nerves has limited the use of mixed nerve action potentials (MNAPs). We recorded MNAPs in 21 patients with an acquired demyelinating neuropathy, 18 age-matched control subjects, and 10 patients with an axonal polyneuropathy. Bipolar and unipolar recordings from median and ulnar nerves were made above the elbow after electrical stimulation of the nerves at the wrist. Antidromic digital sensory action potentials and motor conduction velocity were also recorded for both nerves. In 19 median and 12 ulnar nerves from demyelinating polyneuropathy patients, compared with control subjects, MNAP amplitudes were significantly reduced (mean, 6 μV vs. 31 μV), MNAP velocities were mildly reduced (mean, 50 m/s vs. 62 m/s), motor conduction velocities were significantly reduced (mean, 33 m/s vs. 57 m/s), and MNAPs were significantly dispersed, with markedly prolonged rise times (mean, 2.0 ms vs. 1.0 ms). Compared with the axonal polyneuropathy group, MNAP amplitudes from the median nerve were similarly reduced (mean, 8 μV vs. 9 μV), MNAP velocities were only slightly slower (mean, 52 m/s vs. 58 m/s), but the rise times were significantly prolonged (mean, 2.0 ms vs. 1.2 ms). We conclude that, in acquired demyelinating neuropathies, the onset and, in some cases, the whole MNAP is from afferent fibers, which can be abnormally dispersed, and that, over the same segment, MNAP velocity is less affected than motor conduction velocity. 1995.© 1995 John Wiley &Sons, Inc.     

Somatosensory evoked potentials recorded directly from human thalamus and Sm I cortical area.

Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded from the nucleus ventralis caudalis. They consisted of monophasic or diphasic potentials with mean onset latency of 13.8 ms. More complex SEPs to median nerve stimulation were obtained from the cortex. The SEPs consisted of two major positive waves, P1 and P2, and were recorded over both the precentral and postcentral gyri, suggesting that somatosensory information converges to the motor cortex, probably to be used for the integration of critical motor activity. In two patients, it was noted that the motor representation of facial movements was larger than the correspondent sensory representation on the postcentral gyrus. This larger motor representation of the face and more specifically of the lips and tongue may be related to human acquisition of mimicry and articulation of language.     

An electrophysiological quantitation of the cubital tunnel syndrome

Four hundred and ninety-two ulnar nerves were studied in 237 patients with cubital tunnel syndrome and 233 subjects without clinically apparent ulnar neuropathy. Terminal motor and sensory latencies, motor and sensory conduction velocities, sensory action potential amplitudes and dispersons, and needle electromyography were analysed by a 0 to 10 rating--the EMG score. The patients were clinically graded from 1 (least severe) to 4 (most severe). The median EMG scores of these were 0.9/10 (N = 70); 1.6/10 (N = 81); 4.7/10 (N = 46); and 7.1/10 (N = 56), respectively. The median EMG score for the controls was 0.6/10 (N = 239) and 14.7% had asymptomatic ulnar entrapments. This incidence reached 30% in controls who were 60 years or older. In 25 other controls, the above sulcus sensory action potential was analysed. Its mean dispersion was 4.9 +/- 1.0 s-3. This measurement was significantly prolonged in 84.6% of 13 studies in which the EMG score was 0/10. These patients had either sensory symptoms only or an additional mild sensory deficit. Comparison of the EMG score obtained with sequential studies would allow one to objectively evaluate improvement or deterioration of the clinical state, giving a rational means of determining the need for surgery.     

A case of hereditary motor and sensory neuropathy of neuronal type with retardation of motor development

An atypical case of hereditary motor and sensory neuropathy of neuronal type with retardation of motor development was described. The patient was a 15-year-old boy who had suffered from distal muscle weakness with atrophy of four limbs and deformities of hands and feet since age 6 months. These symptoms were slowly progressive. He had never walked. His parents were not consanguinous. His parents and two siblings were unremarkable on neurological examination and on nerve conduction studies. On neurological examination, he showed severe degree of muscle weakness and atrophy in the distal upper and lower limbs, moderate degree of muscle weakness and atrophy in the proximal upper limbs and slight degree of made weakness and atrophy in the proximal upper limbs. Deep tendon reflexes in four limbs were decreased or absent. Vibration sensation was moderately decreased in the distal parts of four limbs. On the nerve conduction studies, no sensory nerve potential was recorded in the median, ulnar and sural nerves bilaterally. Motor nerve conduction velocity of the right tibial nerve was 21 m/sec and the amplitude of the compound muscle action potential (M-wave) was 0.15 mV, and no M-wave was elicited with the electrical stimulation of the median, ulnar and peroneal nerves. Neelde EMG showed fibrillation potentials and giant spikes with a reduction of the number of motor units. On sural nerve biopsy, the densities of both myelinated and unmyelinated fibers were severely decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spinal segmental somatosensory evoked potentials in lumbosacral radiculopathies

We studied 21 patients with lumbosacral radiculopathy with segmental somatosensory evoked potentials (SEPs) recorded over both spine and scalp following saphenous, superficial peroneal, and sural nerve stimulation. Spinal SEPs were abnormal in 10 patients. In 3 patients, SEPs detected abnormalities not seen on EMG examination. With 1 exception, all anatomic levels of SEP abnormalities matched that of radiographic, EMG, or clinical abnormalities. SEPs were abnormal in 41% of nerve roots shown to be involved by other techniques. SEPs added to the clinical evaluation in 4 patients, but were less accurate than a combination of EMG and radiography in indicating the extent of nerve root involvement. We conclude that spinal SEPs following segmental sensory stimulation are useful in the evaluation of lumbosacral radiculopathies and complement information provided by the EMG. In contrast, scalp-recorded segmental SEPs rarely provide additional useful clinical information.     

Diagnostic importance of somatosensory evoked potentials in the diagnosis of thoracic outlet syndrome

Somatosensory evoked potentials (SEPs) after stimulation of median and ulnar nerves were analyzed retrospectively in a group of 14 patients presenting with rudimentary cervical ribs or ill-healed clavicular fractures, where clinically the possibility of thoracic outlet syndrome was raised. In 5 patients who presented with pain in the arm and hypoesthesia along the ulnar border of the forearm without weakness and wasting in the muscles supplied by the lower trunk of the brachial plexus, the SEPs after both median and ulnar nerve stimulation were normal. In the second group of 9 patients there was weakness and wasting of the lower trunk-supplied muscles. All these patients were treated surgically by excision of abnormal tissues; all of them improved subjectively, and most of them improved strength in the previously affected muscles. SEPs in this group recorded preoperatively showed normal findings after median nerve stimulation, while the potentials after stimulation of ulnar nerve were always abnormal from the affected arm, being delayed, attenuated or even absent at Erb's point, cervical spinal cord and contralateral scalp. The results of this study, which were based on 314 investigations performed in patients with different lesions of the brachial plexus, suggest that abnormal ulnar nerve SEPs in the presence of normal median nerve SEPs are supportive means in the diagnosis of thoracic outlet syndrome, where nervous structures have been endangered. This is in accordance with the most recent reports in the literature.     

Relevance of stimulus duration for activation of motor and sensory fibers: implications for the study of H-reflexes and magnetic stimulation.

Electric stimuli with durations of 0.5-1.0 msec are optimal for studies of H-reflexes. It is more difficult to obtain H-reflexes with shorter duration stimuli or with magnetic stimulation. In order to understand this behavior, we studied the excitation thresholds for motor and sensory fibers in the ulnar, median and tibial nerves using both electric and magnetic stimulation. For short duration electrical stimuli (0.1 msec) the threshold for motor fibers is lower than for sensory fibers. For longer duration electric stimuli (1.0 msec) the threshold for sensory fibers is lower. For magnetic stimulation the threshold for motor fibers is much lower than for sensory fibers. Thus, stimulus duration is a critical parameter for sensory fiber excitation, and current magnetic stimulators are not optimal.     

Riche-Cannieu anastomosis as an inherited trait.

OBJECTIVE: To explore the basis for the Riche-Cannieu anastomosis (RCA) and specifically whether this anomaly is an hereditary characteristic. METHODS: Three individuals from the same family were evaluated after initial studies in the index case indicated an RCA. Nerve conduction, needle electromyography (EMG), and axonal excitability studies of the median and ulnar nerves were undertaken in each case. RESULTS: In all subjects onset thresholds for CMAPs from abductor pollicis brevis (APB) were lower with ulnar nerve stimulation, but of similar latencies when compared with median nerve stimulation. Larger CMAP amplitudes were obtained with ulnar nerve stimulation, at lower stimulus intensities. No sensory anomalies were detected. Needle EMG confirmed dual innervation of APB by both median and ulnar nerves. Nerve excitability studies recorded from APB following ulnar nerve stimulation were within previously established normative limits for the median nerve. In the index case, no innervation anomaly was visible on magnetic resonance imaging from the forearm to hand. CONCLUSIONS: Dual innervation of APB by the median and ulnar nerves consistent with RCA was demonstrated in all 3 family members without co-existent sensory anomalies. SIGNIFICANCE: These findings infer an hereditary basis for RCA, consistent with an autosomal dominant pattern of inheritance.     

Clinical features of the peripheral nerve involvement in necrotizing angitis--characteristics in polyarteritis nodosa and allergic granulomatous angitis

Thirteen patients with peripheral neuropathy caused by necrotizing vasculitis were clinico-pathologically analyzed. These patients consisted of nine classical periarteritis nodosa (PN), four allergic granulomatous angitis (Churg-Strauss syndrome, AGA). All of them were proven to have a necrotizing vasculitis by sural nerve biopsy. The characteristics of peripheral neuropathy of these patients were summarized as follows. 1) Mononeuritis multiplex was a principal features in all patients preferentially localized in common peroneal, sural, radial median and ulnar nerves, with all modality of sensory impairment. 2) Radiation or diffuse deep-pain was a major initial symptom. Since this pain occurs frequently in the manner of sudden onset, the patient can tell the day of onset. 3) Local edema on the skin of involved region was initially observed. 4) Muscular atrophy and weakness was distributed more widely than sensory impairment. 5) Morphometric and teased-fiber study of biopsied sural nerves revealed axonal degeneration as a major pathological process. As compared to myelinated fibers, unmyelinated fibers were likely to be well preserved in morphology and population, which suggests that unmyelinated fibers are relatively resistant to ischemia. 6) Motor and sensory conduction study showed greatly decreased sensory and motor action potentials frequently resulting in absent of recordings. Conduction velocity is almost within normal range or just below the normal. Routine EMG recordings showed active denervation potentials in the involved muscles. 7) Protein in CSF was rarely elevated which suggested involvement of the spinal roots is infrequent. 8) Hypereosinophilia, thrombocythemia, fever, increased erythrocyte sedimentation rate, positive CRP and RA, and polyclonal hypergammaglobulinemia (IgG, IgA) were observed in most cases.     

Nerve conduction studies show no exclusive ulnar or median innervation of the ring finger.

In 2047 hands of 1260 patients referred for an analysis of their brachialgia, distal antidromic sensory conduction was investigated in the median and ulnar nerves. No median sensory nerve action potentials (SNAPs) were obtained from the ring finger (D4) in 257 hands, while ulnar D4 SNAPs were lacking in 38 hands. An obvious lesion of the relevant nerve could be demonstrated in each of these cases. In all remaining cases, in which D4 SNAPs were obtained with both median and ulnar stimulation, it could be excluded that they were due to co-stimulation. These findings are not in agreement with the occurrence of mononeural innervation of D4 as a physiological variation, which has been reported in some clinical and experimental studies. Comparison of SNAP parameters in 183 hands with increased median nerve distal latencies showed conduction to be more impaired in the fibers innervating D4 than in those supplying D3.