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.     

Assessing sensory involvement in lower limb nerve lesions using somatosensory evoked potential techniques

Somatosensory evoked potential (SEP) investigations in 18 patients with lower limb lesions are summarized. Seven patients had problems involving the lateral femoral cutaneous nerve, four the femoral nerve, and seven the sciatic nerve. All lesions were unilateral. SEP techniques were accurate in meralgia paresthetica, and all five patients with demonstrable SEP abnormalities were successfully treated surgically. Delayed recovery of sensory function was shown in two patients with femoral nerve lesions and two patients with sciatic nerve lesions. In patients with sensory symptoms, only an SEP abnormality confined to the nerve distribution provides evidence of a lesion in the sensory pathways and helps to exclude psychologic causes. In a case of peripheral nerve Schwannoma, the presence of a small delay in a case of peripheral SEP supported the preoperative assessment that the tumor was not intrinsic in nature, and this was confirmed at surgery and on subsequent full recovery. The SEP technique allows quantitative assessment of sensory nerve conduction through the peripheral neuron and centripetal pathways.     

New methods for diagnosing lumbar foraminal stenosis using dynamic digital tomosynthesis radiculography

The symptoms of lumbar radiculopathy, in particular foraminal stenosis, often exacerbated when the patient is upright. However, it is difficult to detect the compression of nerve roots while the patient is upright using conventional MRI. In this study, we analyzed the compression of lumbar nerve roots using dynamic digital tomosynthesis radiculography (DTRG) in patients diagnosed with lumbar radiculopathy. And we determined the relationship between leg pain and nerve compression while the patients are either prone or upright. We evaluated 30 patients with unilateral leg pain diagnosed as lumbar radiculopathy by physical examination and MRI. The patients were divided in two groups, one with foraminal stenosis (17 patients) and the other with canal stenosis (13 patients), based on MRI findings. All patients underwent DTRG to determine the diameter of their nerve roots in the foramen while prone and upright. Pain while prone or upright was assessed using a 100-point visual analogue scale (VAS) questionnaire. The VAS for leg pain while upright was significantly higher in the foraminal stenosis group (58 ± 24.7) than it was in the canal stenosis group (19.6 ± 13.2; p = 0.0002)). The nerve root diameter while prone or upright was significantly smaller in the foraminal stenosis group (1.2 ± 0.2 mm) than it was in the canal stenosis group (0.2 ± 0.1 mm; p < 0.0001). DTRG has the potential to visualize nerve compression while the patient is upright to reveal the relevance of foraminal stenosis to clinical findings. DTRG is useful for diagnosis of lumbar foraminal stenosis.     

Cirugía de los tumores neurales del sacro

ObjectivesOur objective is to share our experience in neurogenic tumors of the sacral area, an uncommon disease, and assess approaches, intraoperative techniques, complications and clinical course of patients in a case series.MethodsWe conducted a retrospective analysis of 19 cases of patients with neurogenic tumors in the sacral area who were diagnosed and underwent surgery at our center. Of them, 8 were male and 11 were female. They had a mean age at diagnosis of 51 years (with an age range of 25-78 years). Six patients were asymptomatic and were diagnosed incidentally, while the majority (11 patients) presented with lumbar pain accompanied by other symptoms: pain radiating to the legs, pelvic pain, sensory alterations and loss of strength in the legs. Two patients presented with another primary symptom on diagnosis: pain in the pelvic region and in the left leg. All patients underwent a least one imaging test (MRI/CT scan). Nine patients had tumors limited to the sacrum or with subsequent spread, with surgery via the posterior route. In 6 cases, an exclusively anterior approach was employed owing to the pre-sacral location of the tumor; 4 cases required both an anterior and posterior approach.ResultsThe 6 patients who were asymptomatic at diagnosis continued to have no symptoms after surgery. In 8 patients, symptoms resolved after surgery, and at discharge 4 had pain in the lumbar region or legs, which improved in subsequent consultations. One patient had symptoms consistent with motor and sensory deficit in the right leg deriving from impairment of the external popliteal sciatic nerve. The mean follow-up period was 69 months (6-178 months). Histologically, 17 cases were classified as schwannomas, one case was classified as neurofibroma, and one case was classified as neurofibrosarcoma, which received radiotherapy. Three patients with benign histologies had further surgery for local recurrences.ConclusionsWhen selecting the approach, the large size that these tumors can reach, their relationship with structures, and their anterior or posterior spread should be taken in to account. Resecting the tumor mass as much as possible provides greater benefit to the patient, as this decreases the odds of tumor recurrence without increasing intraoperative and postoperative complications when multidisciplinary teams are also used.     

Spontaneous epidural hematoma as a cause of sciatic pain in a schoolboy

A previously healthy 13-year-old boy began to manifest radiating pain in his left leg after heavy physical exertion during judo training. He also had a sensation of numbness in his left buttock and leg. Initially, the patient was treated conservatively with a clinical diagnosis of disc herniation. However, following 3 months of conservative treatment, there was no relief of pain. Magnetic resonance imaging of the lumbar spine demonstrated an epidural mass causing compression of the dural sac at the L4-L5 disc level. During surgery, the L5 nerve root was found to be severely compressed in the spinal canal because of a chronic epidural hematoma. Following microsurgical removal of this hematoid mass, the patient had a good recovery. Spontaneous epidural hematomas in the lumbar region are rare, and only a few cases presenting with features simulating those caused by a disc herniation have been reported. Our patient represents the first such case described in a child.     

Sciatica due to unusual causes: Tarlov cysts and nerve roots anomalies

Tarlov cysts and nerve roots anomalies usually involve lumbosacral roots and are often asymptomatic. MRI has enabled recognition of many conditions that used to be missed by CT or myelography investigations performed for back and leg pain. However, even without additional compressive impingement (disc hernia, spondylolisthesis or lumbar canal stenosis) these anomalies can be responsible for sciatica, motor deficit and bladder sphincter dysfunction. Tarlov cysts are perinervous dilatations of the dorsal root ganglion. CT and especially MRI can reveal these cysts and their precise relations with the neighboring structures. Delayed filling of the cysts can be visualized on the myelogram. MRI is more sensitive than CT myelography for a positive diagnosis of nerve root anomalies, a differential diagnosis with disc hernia and classification of these anomalies. Surgical treatment is indicated for symptomatic Tarlov cysts and nerve root anomalies resistant to conservative treatment. Better outcome is observed in patients with an additional compressive impingement component. We report two cases of sciatica: one caused by Tarlov cysts diagnosed by MRI and the other by nerve root anomalies diagnosed by CT myelography. In both cases, conservative treatment was undertaken. The clinical, radiological and therapeutic aspects of these disorders are discussed.     

Disturbances of C-fibre-mediated sensibility in lumbosacral disc disease.

In nine patients with chronic lumbosacral disc disease and radicular symptoms clearly restricted to one leg, C-fibre-mediated sensibility was measured by determination of the thresholds for heat pain and warmth on the foot, ipsi- and contralaterally to the nerve root compression. The thresholds were compared with the values for 19 healthy subjects. In the patients the warmth threshold was increased in the ipsilateral dermatome and normal in the contralateral dermatome. In contrast, the heat pain threshold was near normal ipsilaterally but was clearly decreased contralaterally. These findings are discussed with respect to a possible pain sensitisation resulting from nerve root compression.     

椎旁定位腰骶体感诱发电位对腰椎间盘突出症的诊断意义

目的探讨椎旁定位腰骶体感诱发电位（LSSEP）在腰椎间盘突出症中的变化及其诊断意义。方法对84例有L4、L5和S1神经根损害表现的腰椎间盘突出症的患者进行胫后神经体感诱发电位（SEP）、皮节体感诱发电位（DSEP）和椎旁定位LSSEP检查，测定其N40的潜伏期，并对多水平突出症患者的LSSEP与腰椎MRI比较。结果胫后神经SEP检测异常率为42．86％；L5、S1 DSEP检测的异常率为90．48％；椎旁定位LSSEP异常率为95．24％，比胫后神经SEP检测异常率明显增高（P〈0．005）。在L3。椎间盘突出中，以L4的LSSEP异常为主；在L4-5椎间盘突出中以L5的LSSEP为主。结论椎旁定位LSSEP检测可能是诊断腰椎间盘突出症快捷、可靠、敏感的检测方法，其结果与神经根受累水平相一致。     

Proposal of a new criterion for electrodiagnosis of meralgia paresthetica by evoked potentials.

We examined 19 subjects with meralgia paresthetica (bilateral in three cases), recording bilateral somatosensory-evoked potentials (SSEPs) after stimulation of the tibial posterior nerve (TPN) and cutaneous stimulation in the region of the lateral femoral cutaneous nerve (LFCN). We calculated the difference between TPN SSEPs and LFCN SSEPs cortical potentials, identifying a temporal parameter that we termed D(SEP). We defined D(SEP) normal values in a control group. D(SEP) evaluation showed good sensitivity and specificity (85.7% and 82.4%, respectively; accuracy, 83.3%) in discriminating affected limbs from unaffected. The main advantage of this method is to disengage from the necessity of contralateral comparison of LFCN recordings, joined with a reduction of interindividual variability of LFCN SSEPs amplitude and latency that often causes a lower sensitivity of other methods. As an interesting consideration, D(SEP) evaluation appears to mark out a possible subclinical involvement of LFCN in the asymptomatic side of patients with meralgia paresthetica.     

Occult lumbar spinal stenosis.

Twenty-eight patients presenting with low back pain, associated with sciatic or femoral neuropathy, were found to have lateral recess stenosis occurring as a result of hypertrophy of the facet joints, with preservation within normal limits of the sagittal AP diameter of the lumbar canal. Pathology was believed to be traumatic in origin, and the variable nature of the adhesions suggested recurrent inflammation; the hypertrophy of the facet joints may have been the result of traumatic inflammatory hyperaemia. Radiological investigations were unhelpful. The diagnosis of the condition was made at the time of surgical exploration by the findings of alteration of the facet joints, adhesions and fixity of the nerve roots, normal sagittal AP diameter of the canal, and absence of other significant lesions. Gratifying results were obtained with decompression by wide laminectomy with excision of overhanging facet joints and release of adhesions.     

Dermatomal somatosensory evoked potential demonstration of nerve root decompression after VAX-D therapy.

Reductions in low back pain and referred leg pain associated with a diagnosis of herniated disc, degenerative disc disease or facet syndrome have previously been reported after treatment with a VAX-D table, which intermittently distracts the spine. The object of this study was to use dermatomal somatosensory evoked potentials (DSSEPs) to demonstrate lumbar root decompression following VAX-D therapy. Seven consecutive patients with a diagnosis of low back pain and unilateral or bilateral L5 or S1 radiculopathy were studied at our center. Disc herniation at the L5-S1 level was documented by MRI or CT in all patients. All patients were studied bilaterally by DSSEPs at L5 and S1 before and after VAX-D therapy. All patients had at least 50% improvement in radicular symptoms and low back pain and three of them experienced complete resolution of all symptoms. The average pain reduction was 77%. The number of treatment sessions varied from 12 to 35. DSSEPs were considered to show improvement if triphasic characteristics returned or a 50% or greater increase in the P1-P2 amplitude was seen. All patients showed improvement in DSSEPs after VAX-D therapy either ipsilateral or contralateral to the symptomatic leg. Two patients showed deterioration in DSSEPs in the symptomatic leg despite clinically significant improvement in pain and radicular symptoms. Overall, 28 nerve roots were studied before and after VAX-D therapy. Seventeen nerve root responses were improved, eight remained unchanged and three deteriorated. The significance of DSSEP improvement contralateral to the symptomatic leg is emphasized. Direct compression of a nerve root by a disc herniation is probably not the sole explanation for referred leg pain.     

Normal sensory conduction in the saphenous nerve in man.

Measurements of the sensory conduction velocity and the parameters of nerve action potentials in the saphenous nerve offer many advantages, compared with measurements in other nerves of the leg, regarding accuracy and the time required to complete the investigations. Therefore, the electroneurographical examination of the saphenous nerve is recommended in the early diagnosis of polyneuropathies and is indispensable in the exact diagnosis of proximal neuropathies and lesions of the femoral nerve. In the present study we indicate the proximal and distal segments of the saphenous nerve and illustrate the nerve action potentials from 70 normal subjects.     

Isolated posterior femoral cutaneous neuropathy following intragluteal injection

Isolated posterior femoral cutaneous nerve lesions are rarely encountered. Electrophysiological documentation has only been made in a few cases. In this study we evaluated a 22‐year‐old woman with sensory loss and pain in the lower buttock and posterior thigh after left gluteal intramuscular injection. We assessed the posterior femoral cutaneous nerve using an accepted conduction technique. The results showed a normal response on the asymptomatic side, but no response on the symptomatic side. Muscle Nerve, 2009     

Distal lesion of the lateral femoral cutaneous nerve

We report three patients with a typical clinical picture of unilateral meralgia paresthetica in whom routine nerve conduction studies were normal. However, cortical somatosensory evoked potentials were absent after lateral femoral cutaneous nerve (LFCN) stimulation on the affected side. After stimulation of the LFCN in the anterosuperior iliac spine (ASIS) region and recording the responses distal to conventional sites (20 cm from the ASIS), sensory nerve action potentials (SNAPs) were absent in the symptomatic leg, but present in the normal leg. We suggest that thigh paresthesias may be caused by a distal LFCN lesion. Eliciting this requires recording SNAPs distal to conventional sites.     

神经电生理监测辅助下显微手术治疗高颈段椎管内肿瘤

目的 探讨神经电生理监测在显微手术治疗高颈段椎管内肿瘤中应用效果。方法 2011年3月至2014年3月收治高颈段椎管内肿瘤66例,均在神经电生理监测下行显微手术。结果 66例中,11例出现体感诱发电位监测异常,其中8例波幅下降20%~30%,3例波幅下降>50%,均在30min后波幅恢复至20%以下;61例肿瘤全部切除,5例肿瘤部分切除;术后随访12个月,1例复发,1例再次手术。结论 在神经电生理监测下显微手术治疗高颈段椎管内肿瘤,可显著提高临床疗效。     

Cutaneous and mixed nerve silent periods in syringomyelia.

OBJECTIVES AND METHODS: We studied cutaneous and mixed nerve silent periods (CSP, MNSP) in 4 patients with cervical syringomyelia documented by magnetic resonance imaging who on clinical examination presented with unilateral hypalgesia and hypothermesthesia. In addition, we recorded upper and lower extremity somatosensory and motor evoked potentials (SEP, MEP), and cortical silent periods. RESULTS: In all patients, CSP and the later portion of MNSP were absent or shortened on their affected side, while both were normal on their unaffected side. In all patients, SEP latencies were normal following both median and tibial nerve stimulation. In two patients, the amplitude N13 (median nerve SEP), and in one patient each the amplitudes N20 (median nerve SEP) and P37 (tibial nerve SEP) were reduced. Central motor conduction time was prolonged to abductor digiti minimi muscle in one patient on the affected side, but was normal to tibialis anterior muscle in all patients. Cortical silent periods where present bilaterally in spite of unilateral complete absence of CSP and MNSP in two subjects tested. Loss of CSP and MNSP were a sensitive parameter of spinal cord dysfunction in syringomyelia. The cervical median nerve SEP response N13 reflected gray matter involvement, while corticospinal tract dysfunction was less frequently observed. CONCLUSION: Our data suggest that CSP and later portion of MNSP are generated at the spinal level by the same small myelinated A-delta fibers, and that their central network is distinct from large diameter fiber afferents and efferents.     

Dermatomal somatosensory evoked potential demonstration of nerve root decompression after VAX-D therapy

Abstract

Reductions in low back pain and referred leg pain associated with a diagnosis of herniated disc, degenerative disc disease or facet syndrome have previously been reported after treatment with a VAX-D table, which intermittently distracts the spine. The object of this study was to use dermatomal somatosensory evoked potentials (DSSEPs) to demonstrate lumbar root decompression following VAX-D therapy. Seven consecutive patients with a diagnosis of low back pain and unilateral or bilateral L5 or S1 radiculopathy were studied at our center. Disc herniation at the L5-S1 level was documented by MRI or CT in all patients. All patients were studied bilaterally by DSSEPs at L5 and S1 before and after VAX-D therapy. All patients had at least 50% improvement in radicular symptoms and low back pain and three of them experienced complete resolution of all symptoms. The average pain reduction was 77%. The number of treatment sessions varied from 12 to 35. DSSEPs were considered to show improvement if triphasic characteristics returned or a 50% or greater increase in the P1-P2 amplitude was seen. All patients showed improvement in DSSEPs after VAX-D therapy either ipsilateral or contralateral to the symptomatic leg. Two patients showed deterioration in DSSEPs in the symptomatic leg despite clinically significant improvement in pain and radicular symptoms. Overall, 28 nerve roots were studied before and after VAX-D therapy. Seventeen nerve root responses were improved, eight remained unchanged and three deteriorated. The significance of DSSEP improvement contralateral to the symptomatic leg is emphasized. Direct compression of a nerve root by a disc herniation is probably not the sole explanation for referred leg pain. [Neurol Res 2001; 23: 706-714]     

Laminar organization of the extraocular muscles of the rabbit.

Studies of bilateral hemispheric somatosensory evoked potentials (SEP) were carried out on 17 comatose patients following closed-head injury. Control evoked potentials were obtained from 74 normal volunteers. A prognosis of potential recovery or nonrecovery from coma was made in all 17 patients based on the SEP analyses. All subjects underwent bilateral median and peroneal nerve stimulation and responses were averaged from scalp electrodes placed over the somatotopic sensory cortex for the wrist and leg. The prognostic outcome of all 17 patients was accurately predicted following SEP analysis. Results show that 4 of 17 patients with prognoses of “positive recovery” had eight defined SEP peaks present within a time base analysis of 300 ms. Twelve patients with prognoses of “negative recovery” had five or less SEP peaks present within a time base of 500 ms. The majority of the “negative recovery” patients showed only SEP primary waveform components consisting of two peaks. The data suggest a potentially useful method using SEP analysis to prognosticate the possible recovery from clinical coma.     

Recovery functions of common peroneal, posterior tibial and sural nerve somatosensory evoked potentials.

We studied recovery functions of the somatosensory evoked potentials (SEPs) of common peroneal (CPN), posterior tibial (PTN) and sural nerves (SN) using a paired conditioning-test paradigm. The interstimulus interval (ISI) of paired stimuli ranged from 2 to 400 msec. In all SEPs with ISIs of 12-20 msec, the amplitude recovery was close to or beyond 100% of the control response, though their latencies and wave forms were not the same as the control. Further increases of the ISI resulted in significant depression of SEP (late phase suppression), most markedly in CPN, and less prominently in SN-SEP. With a longer than 50 msec ISI there was progressive recovery of SEP, but full recovery differed depending on the nerve stimulated; 400 msec ISI was required for CPN-, 250 msec for PTN- and 100 msec for SN-SEP. The peroneal nerve block by local anesthetic injected just distal to the stimulus electrodes abolished the late phase SEP suppression observed before the nerve block. These findings suggest that the late phase SEP suppression is attributable to the "secondary" afferents as a result of activation of peripheral receptors (muscle, joint and/or cutaneous) by the efferent volley initiated from the stimulus point. The greater and longer duration of peripheral receptor activation in CPN than in PTN or SN stimulation could explain the more pronounced and the longer duration of late phase suppression in CPN-SEP.     

Sensory (VEP, BAEP, SEP) and motor-evoked potentials, liquoral and magnetic resonance findings in multiple sclerosis

In order to define the most suitable instrumental protocol for the diagnosis of multiple sclerosis (MS), 41 patients with definite (D = 14), probable (P = 14) and suspected (S = 13) MS were examined with CSF immunology, brain MRI and multimodal evoked potentials. The central motor tracts were also tested. The following alteration rates were found: MRI = 78%, CSF = 63.6%, VEP = 70.0%, median nerve SEP = 50%, peroneal nerve SEP = 68.0%, BAEPs = 35.7%, motor-evoked potentials (MEPs) = 74.0%. Altogether, EPs were abnormal in 90% of cases. Normal MRI with altered EPs were found in 22% of cases, whilst a normal EP battery with defective CSF or MRI findings were found in 7%. Twenty-six out of 27 patients with P or S forms were reclassified into a D one when considering EPs and MRI features.