SOMATOSENSORY EVOKED POTENTIALS: CLINICAL USES
Evoked potentials (EPs) are time-locked responses of the nervous system to external stimuli. Somatosensory evoked potentials (SEPs) are one type of EP, which are generated by stimulation of afferent peripheral nerve fibers elicited by electrical, tactile, or other stimuli. Following either mixed nerve or sensory nerve stimulation, SEPs can be recorded over more proximal portions of the peripheral and central nervous system including peripheral nerves, spinal cord, and/or brain. By stimulating the skin in various dermatomal areas, an SEP may also be recorded (dermatomal SEPor DSEP).
“Short-latency” SEPrefers to that portion of the waveform of an SEPnormally occurring within 25 ms after stimulation of upper limb nerves, 40 ms after stimulation of the peroneal nerve, or 50 ms after stimulation of the tibial nerve. “Long-latency” SEPrefers to that portion of the waveform recorded after 100 ms following stimulation; “mid-latency” SEPrefers to the portion of the waveforms occurring between those 2 time periods.1
SEPs may be useful in studying disorders of the brain and brainstem, spinal cord, dorsal roots, and peripheral nerves. The exact sites of stimulation, and the number of nerves/roots tested is dependent upon the clinical problem presented and the information desired. When possible, recordings should be made from peripheral nerves and over the spinal cord, as well as from the scalp. In order to identify the best cortical waveform, multiple scalp montages are frequently required. In most cases, bilateral recordings are appropriate. At times, special montages may be required.
Developed by the American Association of Electrodiagnostic Medicine’s (AAEM) Somatosensory Evoked Potentials Subcommittee: Chair: George H. Kraft, MD, MS; Members: Michael J. Aminoff, MD, FRCP; Ernest M. Baran, MD; William J. Litchy, MD; and Walter C. Stolov, MD.
The AAEM would also like to acknowledge the help of the following:
Andrew A. Eisen, MD; William W. Campbell, MD, MSHA; and Kevin R. Nelson, MD.
Key Words: evoked potentials • intraoperative • spinal cord • neuropathy • plexopathy
SEPs are often helpful in localizing the anatomic site of somatosensory pathway lesions. SEPs may be used to identify impaired conduction caused by axonal loss (which may result in a reduced amplitude or absent response) and/or demyelination (which may produce prolonged or absent waveforms).
SEPabnormalities are not disease specific, but can indicate afferent conduction impairments associated with certain disorders. SEPs are useful in identifying clinically inapparent abnormalities and lesions causing only vague or equivocal signs or symptoms, and offer a noninvasive, often quantifiable, method of assessing known lesions. SEPs may also be useful in certain conditions in which the diagnosis is uncertain, by indicating involvement of central somatosensory pathways, as well as suggesting the type of involvement (e.g., demyelination).
In addition, SEPs are useful in confirming nonorganic sensory loss. In such cases, SEPs generated from stimulation of virtually any “numb” area may be compared to recordings obtained from asymptomatic contralateral stimulation.
BRAIN AND BRAINSTEM
SEPabnormalities may occur in conditions impairing the somatosensory pathways in the brain and brainstem, including both diffuse and focal disorders. Some of the conditions in which SEPtesting provides useful clinical information are discussed below.
SEPabnormalities, reflecting pathology in the brain or spinal cord, are present in up to 90% of patients with definite multiple sclerosis (MS) and in approximately 50% of MS patients without current sensory signs or symptoms.10
Lower limb (e.g., tibial) SEPs are more likely to be abnormal than upper limb (e.g., median) SEPs.81
However, both upper and lower limb SEPtesting are often indicated because patients may demonstrate abnormalities in only one of these regions.
The most frequently observed SEPchange in MS is the prolongation of central latencies. Amplitude reductions or absence of responses may also be seen. SEPabnormalities in MS are sometimes detected only in montages that selectively record subcortically generated potentials, which are more easily recorded following median nerve stimulation than posterior tibial nerve stimulation.
Other Diseases of Myelin
Other diseases affecting myelin, such as adrenoleukodystrophy,29
and Pelizaeus-Merzbacher disease18
also produce SEPabnormalities. In adrenoleukodystrophy and adrenomyeloneuropathy, SEPs may be abnormal in asymptomatic heterozygotes.
Hereditary System Degenerations
Many patients with Friedreich’s ataxia have abnormal SEPs, demonstrating delayed central conduction or absent short-latency scalp responses.42
Similar abnormalities are found in patients with disorders such as hereditary cerebellar ataxias and hereditary spastic paraparesis.65
SEPs are useful in classifying the type or origin of myoclonus. Abnormally high amplitude SEPs, reflecting enhanced cortical excitability, have been reported in patients with cortical myoclonus.34
These findings are observed in progressive myoclonic epilepsy, late infantile ceroid lipofuscinosis, and in some patients with photosensitive epilepsy.45
EPs are useful in evaluating comatose patients in whom the scope of neurological examination is often limited or pharmacologic paralysis is confounding. Although they are sensitive to lesions impinging on the afferent sensory pathways, mixed nerve SEPs are affected only minimally by the patient’s level of arousal. SEPabnormalities in the comatose patient can, therefore, be interpreted as reflecting specific lesions affecting neural pathways independent of the comatose state, per se. Caution should be exercised when interpreting SEPs in patients on neurosuppressive medications.
Bilateral SEPs may provide prognostic information in patients with severe cerebral injury resulting in coma.6,17,27,39,60
Following severe cerebral injury, absence of both right and left cortical response to median nerve stimulation is a dependably poor prognostic sign. Patients in whom there is unilateral preservation of the initial cortical response, however, may still have functional recovery.32
SEPs can be used to localize the Rolandic fissure, facilitating intraoperative identification of the sensory and motor cortices. This is important clinically in order to avoid excision of the motor cortex, which would be likely to produce clinical deficits.58,59
Similarly, the primary sensory cortex within the interhemispheric fissure may be identified using cortical SEPs following posterior tibial nerve stimulation. SEPs are also used in some medical centers to monitor for cerebral ischemia during vascular surgery or surgery following aneurysmal
In addition, SEPs can be used for functional localization of the thalamus prior to thalamotomy.
In many of the disorders affecting the ascending pathways of the spinal cord (e.g., MS), abnormal findings may be recorded over the spinal cord. Where possible, it is useful to record ascending potentials at appropriate standardized sites over the spinal cord, as well as over the somatosensory cortex. This is technically more feasible in children or young people than in older persons, and in slender persons than in obese persons. Spinal recordings can be obtained with mixed nerve or sensory nerve stimulation, but not with dermatomal stimulation.
Spinal Cord Trauma
The scalp SEPis absent in complete spinal cord injuries when stimulating a nerve below the level of injury, while the SEPis normal or shows a variety of abnormalities in incomplete spinal cord injury.70,74
Segmental SEPs have been used to localize sensory levels in traumatic cervical spinal cord injury.57
SEPs have also been shown to have prognostic value in functional outcome of acute spinal cord injury.41,55,103
Subacute Combined Degeneration
Short- and mid-latency SEPabnormalities have been found in upper- and lower-limb stimulation in patients with vitamin B12
EPdelays generally correlate with the degree of neurological dysfunction, although some abnormalities may be present without clinical evidence of involvement.
Cervical Spondylosis and Myelopathy
Upper- and lower-limb SEPs may be helpful in assessing cervical spondylosis when spinal cord compression is present.100
SEPs appear to be more sensitive to sensory pathway involvement than clinical sensory testing in myelopathy; however, the correlation of SEPs with radiographic data may be poor.101
Additional montages may be required to obtain the most information about cervical spondylotic myelopathy.71
SEPs are useful in evaluating the effect of compression of the posterior columns in syringomyelia.7
Segmental (i.e., dermatomal [DSEP]) testing may be useful to help delineate the neurophysiologic boundaries of the syrinx.
Hereditary Spastic Paraplegia
Abnormal cervical SEPs to median nerve stimulation in hereditary spastic paraplegia with normal peripheral nerve conduction have been reported.91
These findings indicate selective degeneration of the centripetal processes derived from the dorsal root ganglion cells.
SEPabnormalities have been shown to be helpful in assessing peripheral and central sensory fibers in chronic renal failure73
and in juvenile diabetes.13
Transverse Myelitis and Multiple Sclerosis
Spinal cord lesions may produce conduction slowing or block. SEPs elicited by stimulation below the level of the lesions can have prolonged latencies, low amplitudes, or absent responses.44,80
Lower-limb SEPs have a higher yield for detecting abnormalities in MS81
(see previous section: Brain and Brainstem).
SEPs have been used to help clarify deficits in patients with vascular spinal cord lesions and arteriovenous malformations.80
Abnormalities typically consist of low amplitude or absent responses, rather than prolonged latencies.49
Spinal Cord Tumors
SEPs have been used for assessment of spinal cord tumors to determine the impairments in the various physiologic pathways. In addition, DSEPstudies can help establish the boundaries of physiological unaffected neural tissue; this assists in surgical management.
SEPs have been found useful in patients with myelomeningocele by providing information about physiologic and functional deficits.77
Tethered Cord Syndrome
Posterior tibial SEPs have been shown to be sensitive indicators of neurological impairment in children and young adults with tethered cord syndrome.98
Abnormalities in lumbar spine EPs, delayed or reduced amplitude scalp responses, and/or delays in central conduction have been documented.75
The severity of the SEPresponses correlates with the severity of both clinical and intraoperative findings. Changes in preoperative versus postoperative SEPs correlate with functional outcome after untethering.
Spinal Cord Monitoring
In many medical centers, SEPmonitoring during spinal surgery is the standard of practice. The purpose is to warn of physiologic compromise of the spinal cord or dorsal nerve roots in an anesthetized patient during scoliosis correction, fracture reduction surgery, or other procedures which might injure neural tissue. Change in waveforms is more reliable when recorded over the cord than over the scalp. The most commonly monitored procedures include surgery for scoliosis and surgery following spinal trauma (e.g., stabilization after cervical fracture).16,20,56,66
Intraoperative monitoring is not of proven benefit for routine lumbar or cervical laminectomy or fusion.
VENTRAL ROOTLETS AND ROOTS
SEPand DSEPtechniques are still under evaluation for the study of root disease. In some limited situations, they can be useful in studying disorders peripheral to the spinal cord. Although initial evaluations of nerve root dysfunction were conducted using mixed nerve and sensory nerve SEPtechniques, they were often not useful because they are never single root pathways.25More recent studies have indicated that sensory nerve SEPs and single root DSEPs may provide useful information about rootlet and root dysfunction.83,84,97 Since cutaneous afferent fibers are smaller in diameter (and therefore conduct more slowly) than the 1Aafferent fibers stimulated in standard mixed nerve SEPs, specific reference data are required to analyze the values obtained. Sensory nerve SEPand DSEPlatencies are longer than mixed nerve SEPlatencies obtained over the same distance.69,83 DSEPs have been used to evaluate acute radicu-lopathies.3,4,14,21,24,33,46,47,54,57,61,72,76,78,83,89 Generally speaking, these studies indicate that the yield obtained from DSEPs for acute radiculopathies in an otherwise healthy back is low compared to information obtained from the neurological examination, needle electromyography (EMG) and H-reflex studies.
Lumbosacral Root (Rootlet) Disease:
Radiculopathy and Lumbar Stenosis
SEPs and DSEPs are generally not useful in the evaluation of acute radiculopathies, offering no more information than can be obtained by a careful clinical and needle electromyographic evaluation. For this reason, DSEPstudies for acute lumbosacral radiculopathy are considered investigational at this time. In the assessment of chronic, multi-level multiple rootlet disease, such as that associated with lumbosacral spinal stenosis (LSSS) resulting in chronic compression of relatively long segments of dorsal rootlets, there is a greater physiologic rationale for expecting abnormal DSEPs.47,84,86,93
Preliminary data suggest that DSEPs and sensory nerve SEPs may be useful in defining the neurophysiologic deficits of LSSS and, therefore, potentially may be useful to direct further evaluation and treatment.84,97
Level-bylevel waveforms may be absent, prolonged, and/or reduced in amplitude.
Thoracic Root Disease
While DSEPs may be used to evaluate chronic compressive syndromes at the lumbar and sacral root levels, no data are available for their use in thoracic root disorders. Therefore, DSEPstudies for the evaluation of thoracic root disease must be considered investigational at this time.
Cervical Root Diseases
Although the few studies of DSEPtesting for cervical root disease report sensitivities in the range of 65% to 85%, specificities are poor. There is still controversy about whether or not they provide more useful information than does the clinical evaluation and needle EMG examination.14,54,78,89
Further research is needed to determine their clinical value.
PERIPHERAL NERVOUS SYSTEM
SEPs can be especially useful in assessing the peripheral nerves when severe peripheral nerve disease is present and nerve conduction study (NCS) techniques are inadequate, or when the afferent nerves to be studied present insurmountable technical difficulties.2
In generalized peripheral neuropathies, SEPs have been useful in measuring the afferent fiber conduction velocity of proximal segments and the presence of central responses when the peripheral responses were absent or low. SEPs have been used to evaluate a variety of peripheral nerve disorders, including hereditary neuropathies,8,12
diabetic neuropathy, 9,64,102
and toxic neuropathies.50
The value of SEPs for diagnostic purposes in peripheral nerve disease, particularly acute inflammatory demyelinating polyradiculoneuropathy (AIDP), is not yet established; some reports suggest they are valuable, if the results of conventional electrodiagnostic medicine (EDX) testing methods are normal.30,67,95
In addition, SEPs may be useful in peripheral neuropathies with unobtainable peripheral sensory responses. In such circumstances, they may be the only means of obtaining information about the conduction velocity of peripheral afferent fibers. SEPs may also be helpful in the presence of focal lesions, or when it may be important to know if there are both central and peripheral abnormalities.
Focal nerve lesions,23,40
including entrapment neuropathies, have been studied using SEPs. Carpal tunnel syndrome, lateral femoral cutaneous neuropathy,52
medial and lateral plantar neuropathy,22
and trigeminal neuropathy85
are examples of focal nerve lesions that have been evaluated. These reports have not provided convincing evidence that SEPs provide information that cannot be better obtained with conventional NCS techniques.
Several studies have reported using SEPs to evaluate brachial plexopathy.5,15
In patients with idiopathic brachial plexopathy, there appears to be little advantage over conventional EDX techniques (needle EMG and NCS) for diagnosis or localization. In traumatic plexopathies,35,36
however, SEPs may be useful for detecting superimposed root avulsion by identifying a pattern of preserved peripheral nerve action potentials and absent SEPs. SEPs have also been used to evaluate patients with neurogenic and nonneurogenic thoracic outlet syndrome.11,31,88,96,99
In general, SEPs do not provide additional information beyond that obtained from needle EMG and NCSs.
Evidence of the utility of SEPs for monitoring the integrity of the peripheral nervous system during surgery is insufficient. Nevertheless, SEPtechniques are useful for evaluating the integrity of very proximal peripheral nerve lesions where peripheral nerve recording methods may not be possible. In such cases, intrafieldstimulation with SEPrecording is essential for establishing whether continuity of afferent fibers is present through questionable regions of the peripheral nervous system.48,56,82
The sciatic nerve can be stimulated during hip surgery with SEPrecording. This technique may be useful where peripheral nerve recordings are not feasible.56
Intraoperative monitoring of the brachial and lumbosacral plexus may be valuable. By stimulation of individual components of the plexus, it may be possible to determine the roots that are in continuity with the spinal cord.35,38,43
This summary of the various uses of SEPs is meant to outline the useful indications for these procedures. It is neither meant to serve as an exclusive indicator of recommended uses, nor as a comprehensive source of references. New research is constantly being conducted in this area and, as it is evaluated, indications may change. The physician is therefore urged to closely follow developments in this rapidly changing field.
The review was undertaken by the AAEM at the request of members and third parties. This report is provided as an educational service of the AAEM. It is based on an assessment of the current scientific and clinical information. It is not intended to include all possible methods of care of a particular clinical problem, or all legitimate criteria for choosing to use a specific procedure. Neither is it intended to exclude any reasonable alternative methodologies. The AAEM recognizes that specific patient care decisions are the prerogative of the patient and his/her physician and are based on all of the circumstances involved. This statement was not written with the intent that it be used as a basis for reimbursement decisions.
Approved by the American Association of Electrodiagnostic Medicine: March 5, 1997.
- AAEE: Glossary of terms in clinical electromyography. Muscle Nerve 1987; 10:G12, G18.
- Aminoff MJ: Use of somatosensory evoked potentials to evaluate the peripheral nervous system. J Clin Neurophysiol 1987; 4:135-144.
- Aminoff MJ, Goodin DS, Barbaro NM: Dermatomal somatosensory evoked potentials in unilateral lumbosacral radiculopathy. Ann Neurol 1985; 17:171-182.
- Aminoff MJ, Goodin DS, Barbaro NM: Electrophysiologic evaluation of lumbosacral radiculopathies: Electromyography, late responses, and somatosensory evoked potentials.Neurology1985; 35:1514-1518.
- Aminoff MJ, Olney RK, Parry GJ, Raskin NH: Relative utility of different electrophysiologic techniques in the evaluation of the brachial plexus. Neurology 1988; 38:546-555.
- Anderson D, Bundlie S, Rockswold G: Multimodality evoked potentials in closed head trauma. Arch Neurol 1984; 41:369374.
- Anderson NE, Frith RW, Synek VM: Somatosensory evoked potentials in syringomyelia. J Neurol Neurosurg Psychiatry 1986; 49:1407-1410.
- Aramideh M, Hoogendijk JE, Aalfs CM, Posthumus-Meyjes FE, DeVisser J, Ongerboeer de Visser BW: Somatosensory evoked potentials, sensory nerve potentials and sensory nerve conduction in hereditary motor and sensory neuropathy type I. J Neurol 1992; 239:277-283.
- Bartholomi L, Leili S, Negrin P: Somatosensory evoked potentials in diabetes type I.Electromyogr Clin Neurophysiol 1991; 31:43-46.
- Chiappa K: Short-latency somatosensory evoked potentials: Interpretation, in Chiappa K (ed): Evoked Potentials in Clinical Medicine.New York, Raven Press, 1990, pp 400-407.
- Chodroff G, Lee DJ, Honet JC: Dynamic approach in the diagnosis of thoracic outlet syndrome using somatosensory evoked responses. Arch Phys Med Rehabil1985; 66:3-6.
- Cosi V, Lombardi M, Zandrini C, Gerosa E, Callieco R: Somatosensory evoked potentials in Charcot-Marie-Tooth disease.Neurophysiol Clin 1989; 19:359-365.
- Cracco JB, Castells S, Mark E: Spinal somatosensory evoked potentials in juvenile diabetes. Ann Neurol 1984; 15:55-58.
- D-Alpa F, Sallemi G, Triffiletti L: Cervical SEPs from radicular (digital) upper limb nerves stimulation. Acta Neurol 1986; 8:602-609.
- Date ES, Rappaport M, Ortega HR: Dermatomal somatosensory evoked potentials in brachial plexus injuries. Clin Electroencephalogr 1991; 22:236-249.
- Dawson EG, Sherman JE, Kanim LE, Nuwer MR: Spinal cord monitoring. Results of the Scoliosis Research Society and the European Spinal Deformity Society Survey. Spine 1991; 16:S361-S364.
- De Weerd A, Groeneveld C: The use of evoked potentials in the management of patients with severe cerebral trauma. Acta Neurol Scand 1985; 72:489-494.
- DeMeirleir L, Taylor M, Logan W: Multimodal evoked potential studies in leukodystrophies in children. Can J Neurol Sci1988; 15:26-31.
- Dreyfuss P, Dumitru D, Prewitt-Buchanan L: Intercostal somatosensory evoked potentials. Anew technique. Am J Phys Med Rehabil 1993; 72:144-150.
- Ducker TB, Brown RH: Neurophysiology and Standards of Spinal Cord Monitoring.New York, Springer-Verlag, 1988.
- Dumitru D, Dreyfuss P: Dermatomal/segmental somatosensory evoked potential evaluation of L5/S1 unilateral/ unilevel radiculopathies. Muscle Nerve 1996; 19:442-449.
- Dumitru D, Kalantri A, Dierschke B: Somatosensory evoked potentials of the medial and lateral plantar and calcaneal nerves.Muscle Nerve 1991; 14:665-671.
- Dumitru D, Maquis S: Posterior femoral cutaneous nerve neuropathy and somatosensory evoked potentials. Arch Phys Med Rehabil1988; 69:44-45.
- Dvonch V, Scarff T, Bunch WH, Smith D, Boscardin J, Lebarge H, Ibrahim K: Dermatomal somatosensory evoked potentials: Their use in lumbar radiculopathy. Spine 1984; 9:291-293.
- Eisen AA: AAEE Minimonograph #19: The Somatosensory Evoked Potential. Rochester, Minnesota, American Association of Electromyography and Electrodiagnosis, 1982: (Renamed American Association of Electrodiagnostic Medicine.)
- Fine EJ, Hallett M: Neurophysiological study of subacute combined degenertion. J Neurol Sci1980; 45:331-336.
- Frank L, Murgiuele T, Etheridge J Jr: Prediction of chronic vegetative state in children using evoked potentials. Neurology 1985; 35:931-934.
- Friedman W, Chadwick G, Venhoeven F, Mahla M, Day A: Monitoring of somatosensory evoked potentials during surgery for middle cerebral artery aneurysms. Neurosurgery 1991; 29:83-88.
- Garg B, Markand O, Demyer W, Warren C: Evoked response studies in patient with adrenoleukodystrophy and heterozygous relatives. Arch Neurol 1983; 40:356-359.
- Gilmore RL, Nelson KR: SSEPand F-wave studies in acute inflammatory demyelinating polyradiculoneuropathy. Muscle Nerve 1989; 12:538-543.
- Glover JL, Worth RM, Bendick PJ: Evoked responses in the diagnosis of the thoracic outlet syndrome. Surgery 1981; 89:86-93.
- Goldie W: Brainstem auditory and short latency somatosensory evoked responses in brain death. Neurology 1981; 31:248-256.
- Green J, Gildemeister R, Hazelwood C: Dermatomally stimulated somatosensory cerebral evoked potentials in the clinical diagnosis of lumbar disc disease. Clin Electroencephalogr 1983; 14:152-160.
- Hallett M, Chadwick D, Marsden C: Cortical reflex myoclonus.Neurology1979; 29:1107-1125.
- Hallikainen H, Partenen J, Mervaala E: The importance of neurophysiologic evaluation of plexus brachial injury. Electromyogr Clin Neurophysiol 1993; 33:67-71.
- Hashimoto T, Mitomo M, Hirabuki N, Miura T, Kawai R, Nakamura H, Kawai H, Oho K, Kozuka T: Nerve root avulsion of birth palsy: Comparison of myelography with CT myelography and somatosensory evoked potential. Radiology 1991; 178:841-845.
- Haupt W, Horsch S: Evoked potential monitoring in carotid surgery. Areview of 994 cases. Neurology1992; 42:335-383.
- Hickey C, Gugiono LD, Aglio LS, Mark JB, Son SL, Maddi R: Intraoperative somatosensory evoked potential monitoring predicts peripheral nerve injury during cardiac surgery. Anesthesiology1993; 78:29-35.
- Hume A, Cant B: Central somatosensory conduction after head trauma.Ann Neurol 1981; 10:411.
- Ito J, Yamao S, Kameeyama M: Analysis of somatosensory evoked potentials in peroneal palsy. Acta Neurol Scand 1987; 75:385-390.
- Jacobs S, Sarlo F, Baran E, Herbison G, Ditunno J: Extensor carpi radialis recovery predicted by qualitative SEPand clinical examination in quadriplegia. Arch Phys Med Rehabil 1992; 73:790-793.
- Jones P, Carroll W, Halliday A: Peripheral and central somatosensory nerve conduction in Charcot-Marie-Tooth disease and comparison with Friedreich’s Ataxia.J Neurol Sci 1983; 61:135-146.
- Jones SJ: Diagnostic and prognostic value of somatosensory evoked potentials in lesions of peripheral nerve and spinal cord. Electroencephalogr Clin Neurophysiol 1987; 39:297301.
- Jorg J, Dullberg W, Koeppen S: Diagnostic value of segmental somatosensory evoked potentials in cases with chronic progressive para- or tetraspastic syndromes, in Dourjon J, Mauguiere F, Revol M (ed): Clinical Application of Evoked Potentials in Neurology.New York, Raven Press, 1982, pp 347-358.
- Kakigi R, Shibasaki H: Generator mechanisms of giant somatosensory evoked potentials in cortical reflex myoclonus. Brain 1987;110:1359-1375.
- Katifi HA, Sedgwick EM: Somatosensory evoked potentials from posterior tibial nerve and lumbosacral dermatomes. Electroencephalogr Clin Neurophysiol 1986; 65:249-259.
- Katifi HA, Sedgwick EM: Evaluation of the dermatomal somatosensory evoked potentials in the diagnosis of lumbosacral root compression. J Neurol 1987; 50:1204-1210.
- Kline DG, Hudson AR: Nerve Injuries.Philadelphia, WB Saunders, 1995.
- Kraft GH, Janczakowski JJ, Slimp JC: Comparison of MRI and SEPin patients with MS and stroke. J Clin Neurophysiol 1993; 10(April):243.
- Krarup-Hansen A, Fugleholm K, Helweg-Larsen S, Hauge EN, Scmalbruch H, Trojaborg W, Krarup C: Examination of distal involvement in cisplatin-induced neuropathy in man. An electrophysiological and histological study with particular reference to touch receptor function. Brain 1993; 116:10171041.
- Krumholz A, Weiss HD, Goldstein PJ, Harris KC: Evoked responses in vitamin B12 deficiency. Ann Neurol 1981; 9:407409.
- Lagueny A, Deliac MM, Deliac P, Durandeau A: Diagnostic and prognostic value of electrophysiologic tests in meralgia paresthetica.Muscle Nerve 1991; 14:51-56.
- Lam A, Manninem P, Ferguson G, Natau W: Monitoring electrophysiologic function during carotid endarterectomy. Anesthesiology1991; 75:15-21.
- Leblhuber F, Reisecker F, Boehm-Jurkovic H: Diagnostic value of different electrophysiologic tests in cervical disk prolapse.Neurology 1988; 38:1879-1881.
- Li C, Houlden DA, Rowed DW: Somatosensory evoked potentials and neurological grades as predictors of outcome in acute spinal cord injury. J Neurosurg 1990; 72:600-609.
- Loftus CM, Traynelis VC: Intraoperative Monitoring Techniques in Neurosurgery.New York, McGraw-Hill Inc, 1994.
- Louis AA, Gupta P, Perkash I: Localization of sensory levels in traumatic quadriplegia by segmental somatosensory evoked potentials. Electroencephalogr Clin Neurophysiol 1985; 62:313-316.
- Lueders H, Dinner D, Lesser R, Morris H: Evoked potentials in cortical localization. J Clin Neurophysiol 1986; 3:75-84.
- Lueders H, Lesser R, Hahn J, Dinner D, Klem G: Cortical somatosensory evoked potentials in response to hand stimulation. J Neurosurg1983; 58:885-894.
- Lutschg J, Pfenninger J, Ludin H: BAEPs and early SEPs in neurointensively treated comatose children. Am J Dis Child 1983; 137:421-426.
- Machida M, Asai T, Sato K, Toriyama S, Yamada T: New approach for diagnosis in herniated lumbosacral disc. Dermatomal somatosensory evoked potentials (DSEPs). Spine 1986; 11:380-384.
- Moglia A, Zandrini C, Alfonsi E, Rondanelli EG, Bono G, Nappi G: Neurophysiological markers of central and peripheral involvement of the nervous system in HIV infection. Clin Electroencephalogr 1991; 22:193-198.
- Momma F, Wang A, Symon L: Effects of temporary arterial occlusion on somatosensory evoked responses in aneurysm surgery. Surg Neurol 1987; 27:343-352.
- Nakamura R, Noritake M, Hosoda Y, Kamakura K, Nagata N, Shibasaki H: Somatosensory conduction delay in central and peripheral nervous system of diabetic patients. Diabetes Care 1992; 15:532- 535.
- Nuwer M, Perlman S, Packwood J, Kark R: Evoked potential abnormalities in the various inherited ataxias. Ann Neurol 1983; 13:20-27.
- Nuwer MR, Daube J, Fischer C, Schramm J, Yingling CD: Neuromonitoring during surgery. Report of an IFCN Committee. Electroencephalogr Clin Neurophysiol 1993; 87:263-276.
- Olney RK, Aminoff MJ: Electrodiagnostic features of the Guillain- Barré syndrome: The relative sensitivity of different techniques.Neurology 1990; 40:471-475.
- Parry GJ, Aminoff MJ: Somatosensory evoked potentials in chronic demyelinating peripheral neuropathy. Neurology 1987; 37:313-316.
- Perlik S, Fisher MA, Dushyant VP, Slack C: On the usefulness of somatosensory evoked responses for the evaluation of lower back pain. Arch Neurol 1986; 43:907-913.
- Perot PL, Vera CL: Scalp-recorded somatosensory evoked potentials to stimulation of nerves in the lower extremities and evaluation of patients with spinal cord trauma. Ann NY Acad Sci1982; 388:359-368.
- Restuccia D, Di Lazzaro V, Valeriani M, Aulisa L, Galli M, Tonali P, Mauguière F: The role of upper limb somatosensroy evoked potentials in the management of cervical spondylotic myelopathy: Preliminary data. Electroencephalogr Clin Neurophysiol 1994; 92:502-509.
- Rodriguez AA, Kanis L, Rodriguez AA: Somatosensory evoked potentials from dermatomal stimulation as an indicator of L5 and S1 radiculopathy. Arch Phys Med Rehabil1987; 68:366-368.
- Rossini PM, Treviso M, DiStefano E, DiPaolo B: Nervous impulse propagation along peripheral and central fibers in patients with chronic renal failure. Electroencephalogr Clin Neurophysiol 1983; 56:293-303.
- Rowed DW, McLean JAG, Tator CH: Somatosensory evoked potentials in acute spinal cord injury: Prognostic value. Surg Neurol 1978; 9:203-210.
- Roy MW, Gilmore R, Walsh JW: Evaluation of children and young adults with tethered spinal cord syndrome. Utility of spinal and scalp recorded somatosensory evoked potentials. Surg Neurol 1986; 26:241-248.
- Scarff TB, Dallmann DE, Toleikis JR: Dermatomal somatosensory evoked potentials in the diagnosis of lumbar root entrapment. Surg Forum 1981; 32:489-491.
- Scarff TB, Toleikis JR, Bunch WH, Parrish S: Dermatomal somatosensory evoked potentials in children with myelomeningocele.Z Kinderchir Grenzgeb1979; 28:384-387.
- Schimscheimer RJ, Ongerboer de Visser BW, Bour LJ: Digital nerve somatosensory evoked potentials and flexor carpi radialis H reflexes in cervical disc protrusion and involvement of the sixth or seventh cervical root: Relations to clinical and myelographic findings. Electroencephalogr Clin Neurophysiol 1988; 70:313-324.
- Schramm J, Koht A, Schmidt G, Pechstein V, Taniguichi M, Fahlbusch R: Surgical and electrophysiological observations during clipping of 134 aneurysms with evoked potentials monitoring. Neurosurgery 1990; 26:61-70.
- Schramm J, Oettle GJ, Pichert T: Clinical application of segmental somatosensory evoked potentials (SEP) - Experience in patients with non-space occupying lesions, in Barber C (ed):Evoked Potentials. Lancaster, MTPPress, 1980, pp 455-465.
- Slimp JC, Janczakowski J, Seed MD, Kraft GH: Comparison of median and posterior tibial nerve somatosensory evoked potentials in ambulatory patients with definite multiple sclerosis.Am J Phys Med Rehabil1990; 69:293-296.
- Slimp JC, Kliot M: Electrophysiological monitoring: Peripheral nerve surgery, in Andrews RJ (ed): Intraoperative Neuroprotection Baltimore, Williams & Wilkins, 1996, pp 375-392.
- Slimp JC, Rubner DE, Snowden ML: Dermatomal somatosensory evoked potentials: Cervical, thoracic, and lumbosacral levels.Electroencephalogr Clin Neurophysiol 1992; 84:55-70.
- Snowden ML, Haselkorn J, Kraft GH, Bronstein A, Slimp J, Stolov W: Dermatomal somatosensory evoked potentials in lumbosacral spinal stenosis. Muscle Nerve 1992; 15:10361044.
- Stechison MT: The trigeminal evoked potential: Part II, Intraoperative recording of short latency responses. Neurosurgery 1993; 33:639-643.
- Stolov WC, Turella G, Slimp JC, Bigos SJ. Somatosensory evoked potentials (SSEPs) to mixed nerve and dermatomal stimulation and EMG in lumbar spinal stenosis. VII International Congress of Electromyography and Related Clinical NeurophysiologySorrento, Italy, 1987.
- Symon L, Momma F, Murota T: Assessment of reversible cerebral ischaemia in man: Intraoperative monitoring of somatosensory evoked response. Acta Neurochir Suppl 1988; 42:3-7.
- Synek VM: Diagnostic importance of somatosensory evoked potentials in the diagnosis of the thoracic outlet syndrome. Clin Electroencephalogr 1986; 117:112-116.
- Synek VM: Somatosensory evoked potentials after stimulation of digital nerves in upper limbs: Normative data. Electroencephalogr Clin Neurophysiol 1986; 65:460-463.
- Takakura H, Nakano C, Kasagi S: Multimodality evoked potentials in progression of metachromatic leukodystrophy. Brain Dev 1985; 7:424-430.
- Thomas PK, Jeffreys JGR, Smith IS, Loulakakis D: Spinal somatosensory evoked potentials in hereditary spastic paraplegia.J Neurol Neurosurg Psychiatry1981; 44:243-246.
- Tobimatsu S, Fukui R, Kato M: Multimodality evoked potentials in patients and carriers with adrenoleukodystrophy and adrenomyeloneuropathy. Electroencephalogr Clin Neurophysiol 1985; 62:18-24.
- Tokuhashi Y, Santoh K, Funami S: Aquantitative evaluation of sensory dysfunction in lumbosacral radiculopathy. Spine 1991; 16:1321-1328.
- Tranier S, Durey A, Chevailler B, Liot F: Value of somatosensory evoked potentials in saphenous entrapment neuropathy. J Neurol Neurosurg Psychiatry1992; 55:461-465.
- Vajsar J, Taylor MJ, MacMillan LJ, Murphy EG, Logan WJ: Somatosensory evoked potentials and nerve conduction studies in patients with Guillain-Barré syndrome. Brain Dev 1992; 14:315-318.
- Veilleux M, Stevens JC, Campbell JK: Value of somatosensory evoked potentials in the diagnosis of thoracic outlet syndrome. Muscle Nerve 1986; 9:655-662.
- Walk D, Fisher MA, Doundoulakis SH, Hemmati M: Somatosensory evoked potentials in the evaluation of lumbosacral radiculopathy. Neurology1992; 42:1197-1202.
- Yamada S, Knierim D, Yonekura M, Schultz R, Maeda G: Tethered cord syndrome. J Am Paraplegia Soc 1983; 6:58-61.
- Yiannikas C, Walsh JC: Somatosensory evoked responses in the diagnosis of the thoracic outlet syndrome. J Neurol Neurosurg Psychiatry1983; 46:234-240.
- Yiannikas C, Shahani BT, Young RR: Short-latency somatosensory evoked potentials from radial, median and ulnar peroneal nerve stimulation in the assessment of cervical spondylosis: Comparison with conventional electromyography.Arch Neurol 1986; 42:1264-1271.