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 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.     

The value of ulnar somatosensory evoked potentials (SEPs) in cervical myelopathy

In 57 patients with clinical signs and surgical documentation of compressive myelopathy, ulnar nerve somatosensory evoked potentials (SEPs) were more sensitive (with 74% abnormal) than either median or tibial nerve SEPs. The most frequent abnormalities were reduced or absent neck evoked responses and prolonged central conduction time. All subjects who had an SEP abnormality were identified by combined tibial and ulnar SEPs. Median nerve SEP added no additional information. Normal ulnar and tibial nerve SEPs were also able to exclude major cord damage in patients with cervical radiculopathy but little evidence of myelopathy.     

Validity of median nerve somatosensory evoked potentials in the diagnosis of supraclavicular brachial plexus lesions

Experience with median nerve SEPs in the diagnosis of brachial plexus lesions is analysed in 49 patients selected from a total material of 264 cases with brachial plexus problems tested by SEP techniques. Median nerve SEPs were always compared with the results of SEPs after stimulation of at least one other nerve relevant to the site of the lesion as suspected clinically and electromyographically. All patients presented with unilateral brachial plexus problems and all root lesions were verified by clinical presentation, EMG studies, myelogram or surgery. There were 19 brachial plexus injuries, 13 cases with cervical spondylopathic radiculopaties without myelopathy and 7 patients presented brachial plexopathy with systemic cancer. It was found that median nerve SEPs were always normal in injuries of upper trunk and root avulsions confined to one or two root levels. Median nerve SEPs were abnormal in multiple trunk lesions and multiple root avulsions. In patients with spondylopathic radiculopathies median nerve SEPs were normal apart from one case where involvement of multiple roots was present. Median nerve SEPs were useful in assessing patients presenting brachial plexus problems in the presence of systematic cancer apart from cases where lower trunk involvement was present. In general, median nerve SEPs are useful if they are combined with SEP testing of other nerves anatomically more closely related to the problem as outlined clinically and electromyographically.     

Abnormal somatosensory evoked potentials indicate compressive cervical myelopathy in mucopolysaccharidoses

Compressive myelopathy at the cranio-cervical junction is a complication of mucopolysaccharidoses (MPS). To detect cervical myelopathy we recorded median and posterior tibial nerve SEPs in 15 patients aged 2.4-33.4 years (median 8.8 years) with MPS I-S (n = 3), MPS IVA (n = 8) and MPS VI (n = 4). In addition to the cortical waveforms we recorded the subcortical median nerve SEPs N13b and P13 generated near the cranio-cervical junction and the lemniscal P30 after posterior tibial nerve stimulation. MRI studies in 13 subjects revealed spinal cord compression at the cranio-cervical junction in 10 patients; 5 patients had an increased signal intensity on the T2-weighted initial MRI indicating high cervical myelomalacia and 4 patients had clinical signs of cervical myelopathy. We did not find a relationship between the SEPs and spinal cord compression. Abnormal SEPs were found in the patients with MRI evidence of myelomalacia (sensitivity 1.0, specificity 1.0) and correspondingly in the patients with clinical signs (sensitivity 1.0, specificity 0.91). The SEPs consequently deteriorated in 2 subjects of 7.3 and 10.3 years of age. Abnormal SEPs indicated subclinical cervical myelopathy in 3 subjects. Cervical cord compression may be present before occurrence of clinical or electrophysiological evidence of myelopathy. However, we feel that the SEP analysis is useful to detect functional impairment of the cervical cord in patients with MPS.     

Somatosensory conduction times and peripheral, cervical and cortical evoked potentials in patients with cervical spondylosis.

Peripheral, cervical and cortical somatosensory evoked potentials after median or ulnar nerve stimulation were recorded in 21 patients with cervical spondylosis with radiculopathy or myelopathy. The test was normal when pain and paraesthesias were the only symptoms, while pathological in radiculopathy with objective neurological signs. The results varied in patients with cervical myelopathy.     

Somatosensory evoked potentials in patients with cervical spondylotic myelopathy

Somatosensory evoked potentials (SEPs) to posterior tibial nerve (PTN) and median nerve (MN) stimulations were recorded in 30 patients with cervical spondylotic myelopathy. Measurements performed include N20-P2 interpeak latency (IPL) for PTN-SEPs, EP-N13 IPL and EP-N20 IPL for MN-SEPs. Limits of normal IPL were defined by the mean + 3S.D. of the normal control group. PTN-SEPs was more sensitive (with 73.3% abnormal) than MN-SEPs (with 33.3% abnormal) and strongly correlated with the clinical signs of posterior column, but not with those of anterolateral column indicated by superficial sensory disturbances and spasticity of lower limbs. Severities of cord compression (sagital diameter/transverse diameter ratio) calculated from the picture of metrizamide CT were not correlated with SEPs findings and clinical signs. In patients with cervical myelopathy, SEPs, especially PTN-SEPs, were thought to be very useful examination.     

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.     

Somatosensory evoked responses in the diagnosis of thoracic outlet syndrome.

A study was made of 11 patients with cervical rib, and one patient with Klippel-Fiel syndrome and enlarged transverse processes to determine whether evoked potentials recorded from both Erb's points and the cervical spine in response to median and ulnar nerve stimulation provided information additional to that obtained by EMG and peripheral conduction studies. It was found that in seven patients who had pain and paraesthesias but no objective neurological signs both the peripheral and central conduction studies were within normal limits. By contrast, of five patients who had objective signs, conventional EMG and conduction studies were abnormal in three patients, but abnormalities of the evoked potentials obtained from ulnar nerve stimulation were obtained in all five patients. It is suggested that this application of evoked potential estimation is a useful addition to the more conventional peripheral investigations.     

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.     

Short latency somatosensory evoked potentials from radial, median and ulnar nerve stimulation in man

Short latency somatosensory evoked potentials (SEPs) were elicited by stimulation at the wrist of median, radial, and ulnar nerves, singly or in combination, using normal subjects. Amplitude of P10 was strikingly lower with radial stimulation than with median stimulation, while ulnar-derived P10 was intermediate in amplitude. This difference probably reflects the antidromic firing of motor fibers contained in median nerves as compared with the superficial branch of radial nerve, which is entirely sensory. Beyond P10, there appear to be no significant differences between median, radial and ulnar-derived SEPs. With simultaneous stimulation of several nerves within one arm, larger potentials were sometimes achieved but with poorer definition of P12 and P14. The clinical utility of radial, ulnar, and median stimulation for localizing peripheral lesions derives from the distinct anatomical pathways of the stimulated fibers through the brachial plexus and from the separable motor and sensory components of P10. SEP is less invasive than EMG; this fact, plus its freedom from sampling error, make it potentially more suitable than conventional EMG for sequentially following a patient's clinical course.     

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.     

Electrophysiologic evaluation of lumbosacral radiculopathies: electromyography, late responses, and somatosensory evoked potentials

We compared the diagnostic utility of EMG, F wave and H-reflex studies, and peroneal and dermatomal SEPs in evaluating 28 patients with clinically unequivocal L-5 or S-1 compressive root lesions. The single most useful electrophysiologic technique was EMG, which often provided evidence of denervation in a myotomal pattern when other electrophysiologic findings were normal. We found abnormal late responses in 14 patients, but always in association with EMG abnormalities. Peroneal-derived SEPs were always normal. Dermatomal SEPs confirmed the diagnosis in seven patients, including two in whom other electrophysiologic studies were normal.     

The use of evoked potentials for clinical correlation and surgical outcome in cervical spondylotic myelopathy with intramedullary high signal intensity on MRI

OBJECTIVE: To investigate the use of motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) for clinical significance and surgical outcome in patients with cervical spondylotic myelopathy (CSM) with intramedullary high signal intensity on T2 weighted MRI. METHODS: Forty nine patients were scored according to the modified Japanese Orthopaedic Association (JOA) score for cervical myelopathy. MEP and SEP studies were performed and the results were categorised as normal or abnormal. Thirty nine patients who had received surgical decompression were re-evaluated after 6 months. Surgical outcome was represented by the recovery ratio of the JOA score. RESULTS: Abnormal MEPs were observed in 44 patients (arm: 43; leg: 30). Abnormal SEPs were found in 32 patients: (median: 24; tibial: 23). Patients with abnormal SEPs had a worse JOA score than those with normal SEPs. Thirty nine patients received surgical treatment. Patients younger than 55 had better recovery ratios than those who were 55 or older (p = 0.005, two sample Student's t test). Patients with normal median SEPs also had better recovery ratios than those with abnormal median SEPs (p = 0.007, two sample Student's t test). Among median SEP variables, only N9-20 was significantly associated with recovery ratio (p = 0.016, stepwise linear regression), with age factor controlled (p = 0.025, stepwise linear regression). CONCLUSION: Arm MEP was the most sensitive EP test for detecting myelopathy in patients with chronic CSM. Median and tibial SEPs correlated well with the severity of myelopathy while normal median SEPs correlated with good surgical outcome. Among median SEP variables, only N9-20 correlated with surgical outcome.     

Subcortical somatosensory evoked potentials after median nerve and posterior tibial nerve stimulation in high cervical cord compression of achondroplasia

Children with achondroplasia may have high cervical myelopathy from stenosis of the cranio-cervical junction resulting in neurological disability and an increased rate of sudden death. To detect myelopathy we recorded somatosensory evoked potentials after median nerve (MN) and posterior tibial nerve (PTN) stimulation in 77 patients with achondroplasia aged 0.3–17.8 years (mean 2.7 years). In addition to the conventional technique of recording the cortical components and the central conduction time (CCT) we employed non-cephalic and mastoid reference electrodes to record the subcortical waveforms N13b and P13 (MN-SEP) as well as P30 (PTN-SEP), respectively, which are generated near the cranio-cervical junction. The findings were related to the MRI results. Thirty-four patients had abnormal MRI findings including spinal cord compression (n = 28) and/or myelomalacia (n = 24) at or below the cranio-cervical junction. The sensitivity of the MN-SEPs was 0.74 including all abnormal upper cervical cord MRI findings (specificity 0.98), and the sensitivity was 0.79 (specificity 0.92) for cervical cord compression, respectively. The sensitivity of the PTN-SEPs was 0.52 (specificity 0.93) for all abnormal MRI findings and 0.59 (specificity 0.92) for cervical cord compression. The subcortical SEPs N13b and P13 as well as P30 were more sensitive than the conventional recordings. The MN-SEPs, notably the subcortical tracings, are useful for the detection of cervical myelopathy in children with achondroplasia. The PTN-SEPs are less sensitive. However, the tibial nerve SEPs might contribute additional information from the lumbar or thoracic spinal cord, which was, however, not tested in this study.     

The role of somatosensory evoked potentials in the diagnosis of AIDS-associated myelopathy

BACKGROUND: Although AIDS-associated vacuolar myelopathy is detected in >50% of autopsy cases, it is often unrecognized during life. The clinical assessment is often difficult because of concurrent peripheral neuropathy and lack of specific diagnostic markers. Somatosensory evoked potentials (SEPs) have been successfully used to evaluate central conduction in a number of diseases involving the spinal cord. OBJECTIVES: To assess the diagnostic yield of SEPs in AIDS-associated myelopathy. METHODS: We recorded tibial and median nerve SEPs in 69 HIV-infected subjects referred for evaluation of lower extremity neurologic abnormalities. Stimulation of the peroneal nerve at the popliteal fossa was performed in patients with absent response to ankle stimulation. RESULTS: HIV-infected subjects had significantly delayed latencies of both peripheral and central potentials, suggesting a combination of peripheral and CNS abnormalities. Analysis of peripheral and central latencies allowed us to discriminate between neuropathy and myelopathy in individual patients. Abnormalities of tibial central conduction time (CCT) correlated with clinical diagnosis of myelopathy. There was no significant difference in median CCTs between patients and controls, suggesting that conduction abnormalities were restricted to the thoracolumbar spinal cord. A derived spinal conduction time was a sensitive indicator of central conduction abnormalities in AIDS patients with myelopathy. CONCLUSIONS: The combination of median, posterior tibial, and peroneal SEPs is a valuable tool in the diagnosis of AIDS-associated myelopathy, particularly when myelopathy and peripheral neuropathy coexist. The use of a derived spinal conduction time improves the diagnostic yield of SEPs in AIDS-associated myelopathy.     

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.     

Cutaneous silent periods in intramedullary spinal cord lesions

OBJECTIVE: The neurophysiological assessment of intramedullary spinal cord lesions has been unsatisfactory. Previous studies in patients with syringomyelia suggest that testing of cutaneous silent periods (CSPs) may be useful to assess centromedullary lesions. METHODS: The authors studied nine patients with intramedullary spinal cord lesions of different etiologies. Eight patients with cervical lesions presented with hypalgesia, hypothermesthesia, or pain in at least one upper extremity; five of them had also upper limb weakness or sensory impairment. One patient with a thoracic lesion had normal upper limb function. The authors recorded CSPs in abductor pollicis brevis muscle following digit II and digit V stimulation. Somatosensory evoked potentials (SEPs) were obtained following median and tibial nerve stimulation. Motor evoked potentials (MEPs) were obtained in biceps brachii, abductor digiti minimi and tibialis anterior muscles following transcranial magnetic or electrical stimulation. RESULTS: CSP abnormalities were found in all patients with cervical lesions, but not in the patient with a thoracic lesion. Cortical median nerve SEPs had normal latencies in all patients, while tibial nerve SEPs, upper limb MEPs, and lower limb MEPs were delayed in five patients each. In one patient, abnormal CSP were the only neurophysiological finding. CSP abnormalities were associated with hypalgesia and hypothermesthesia in 95% of the studies. CONCLUSION: Upper extremity CSP testing is a sensitive neurophysiological technique for the assessment of cervical intramedullary lesions. In particular, abnormal CSPs are highly associated with spinothalamic dysfunction.     

Motor and somatosensory evoked potentials in asymptomatic spondylotic cord compression.

To assess whether electrophysiological tests are of use in differentiating between patients with asymptomatic cervical stenosis and patients with clinical evidence of myelopathy, we studied motor evoked potentials (MEPs) to magnetic brain stimulation and somatosensory evoked potentials (SEPs) in patients with asymptomatic cervical cord compression and compared the results to healthy age-matched controls. The MEPs were normal in 23 of 25 patients and SEPs in 22 of 23 patients. Thus, MEPs and SEPs are normal in most cases of asymptomatic cervical stenosis. As previous studies have shown MEPs, and to a lesser extent SEPs, to be sensitive in the detection of spondylotic myelopathy, our data indicate that MEP and SEP may be clinically useful for differentiating patients with cervical stenosis who have myelopathy from those who have not.     

Somatosensory evoked potentials in Charcot-Marie-Tooth disease

SEPs by median nerve stimulation have been performed in 18 adult patients (12 males and 6 females) affected by CMTD (type I, 13 patients; type II, 5 patients). All patients underwent MCV studies (median, ulnar, peroneal nerve), SCV studies (median and sural nerve), VEP, BAEP. N9 and N13 peaks were not detectable in 7/13 and 5/13 cases (HMSN type I) while cortical N19 were always recorded. Latency values of all responses were moderately or markedly delayed in all cases with HMSN type I, but proved normal or slightly delayed in HMSN type II cases. The prolonged latencies were mainly related to slowing of peripheral conduction. N9-N13 inter-peak was abnormally prolonged in 2 cases and N13-N19 in 2 other cases; both were prolonged in another case. In another 3 cases an abnormal BAEP was recorded. The few patients with abnormal CCT and BAEP probably belong to a borderline form between HMSN and hereditary ataxias.