Clinical Focus

  • Neurology
  • Intraoperative Neurophysiologic Monitoring
  • Electromyography
  • Botulinum Toxin Treatment
  • Neurology, Pediatric

Academic Appointments

Professional Education

  • Fellowship:Stanford University School of Medicine (1992) CA
  • Internship:Stanford University School of Medicine (1988) CA
  • Residency:Stanford University School of Medicine (1991) CA
  • Medical Education:University of Washington School of Medicine (1987) WA
  • Board Certification: Neurology, American Board of Psychiatry and Neurology (1995)
  • MD, University of Washington, Medicine (1987)

Research & Scholarship

Current Research and Scholarly Interests

My clinical interests are in the areas of Intraoperative Neurophysiologic Monitoring (IOM), clinical neurophysiology, electromyopgraphy and in the use of botulinum toxins in the treatment of neurologic disorders. Our IOM group’s research is in the development of new and innovative techniques for monitoring the nervous system during surgical and endovascular procedures and how these alter surgical management and patient outcomes. I am also active in formulating national IOM practice guidelines.


2015-16 Courses


All Publications

  • Detection of inferolateral trunk syndrome by neuromonitoring during catheter angiography with provocative testing. Journal of neurointerventional surgery Le, S., Dodd, R., López, J., Nguyen, V., Cho, S. C., Lee, L. 2013; 5 (2)


    It is not uncommon that endovascular balloon test occlusion (BTO) is performed to assess collateral blood flow and risk of injury of permanent occlusion of the internal carotid artery (ICA). This case is the first reported of detection and reversal of the inferolateral trunk (ILT) syndrome in an awake patient during provocative BTO; prompt recognition of the syndrome effectively prevented permanent neurologic deficits.The case of a 42-year-old woman is reported who had a left sphenoid wing meningioma with extension into the cavernous sinus and who underwent awake catheter angiography with provocative BTO of the ICA. Serial examinations by intraoperative monitoring neurologists and neurointerventionalists detected acute progressive left retro-orbital pressure followed by sudden inability to adduct the left eye, or a left medial rectus palsy, indicative of the ILT syndrome which led to immediate balloon deflation and resolution of the deficits. The hypothesis was that hypoperfusion of the ILT, an arterial branch of the ICA which provides blood supply to several cranial nerves (CN) III, CN V1 and CN V2, caused her acute symptoms.Although cerebral ischemia is a well known complication of endovascular procedures, CN ischemia is a rare potential risk. Knowledge of cerebrovascular anatomy and serial examinations prevented neurologic deficits; this case underscores the added utility of examinations by intraoperative monitoring neurologists and interdisciplinary collaboration.

    View details for DOI 10.1136/neurintsurg-2011-010236

    View details for PubMedID 22345146

  • Evidence-Based Guideline Update: Intraoperative Spinal Monitoring with Somatosensory and Transcranial Electrical Motor Evoked Potentials JOURNAL OF CLINICAL NEUROPHYSIOLOGY Nuwer, M. R., Emerson, R. G., Galloway, G., Legatt, A. D., Lopez, J., Minahan, R., Yamada, T., Goodin, D. S., Armon, C., Chaudhry, V., Gronseth, G. S., Harden, C. L. 2012; 29 (1): 101-108


    To evaluate whether spinal cord intraoperative monitoring (IOM) with somatosensory and transcranial electrical motor evoked potentials (EPs) predict adverse surgical outcomes.A panel of experts reviewed the results of a comprehensive literature search and identified published studies relevant to the clinical question. These studies were classified according to the evidence-based methodology of the American Academy of Neurology. Objective outcomes of postoperative onset of paraparesis, paraplegia, and quadriplegia were used because no randomized or masked studies were available.Four class I and eight class II studies met inclusion criteria for analysis. The four class I studies and seven of the eight class II studies reached significance in showing that paraparesis, paraplegia, and quadriplegia occurred in the IOM patients with EP changes compared with the IOM group without EP change. All studies were consistent in showing all occurrences of paraparesis, paraplegia, and quadriplegia in the IOM patients with EP changes, with no occurrences of paraparesis, paraplegia, and quadriplegia in patients without EP change. In the class I studies, 16% to 40% of the IOM patients with EP changes developed postoperative-onset paraparesis, paraplegia, or quadriplegia. IOM is established as effective to predict an increased risk of the adverse outcomes of paraparesis, paraplegia, and quadriplegia in spinal surgery (four class I and seven class II studies). Surgeons and other members of the operating team should be alerted to the increased risk of severe adverse neurologic outcomes in patients with important IOM changes (level A).

    View details for DOI 10.1097/WNP.0b013e31824a397e

    View details for Web of Science ID 000300634700015

    View details for PubMedID 22353994

  • Neurophysiologic Intraoperative Monitoring of the Oculomotor, Trochlear, and Abducens Nerves JOURNAL OF CLINICAL NEUROPHYSIOLOGY Lopez, J. R. 2011; 28 (6): 543-550

    View details for Web of Science ID 000298821700003

    View details for PubMedID 22146351

  • Neurophysiologic Intraoperative Monitoring of Pediatric Cerebrovascular Surgery JOURNAL OF CLINICAL NEUROPHYSIOLOGY Lopez, J. R. 2009; 26 (2): 85-94


    The surgical and endovascular treatment of cerebrovascular disorders (CVDs) in children, such as cerebral arteriovenous malformations, cavernous malformations, and moyamoya disease, have become commonplace and routine in many centers. As in the adult population, these procedures carry the risk of intraoperative cerebral ischemia. Therefore, similar strategies used to reduce the risk of cerebral ischemia in adults should be used in children. Unfortunately, there are no published studies on the intraoperative use of available techniques to identify, prevent, or potentially reverse cerebral ischemia. The goal of this article is to review the neurophysiologic techniques that may be useful and applicable in the surgical and endovascular treatment of pediatric CVDs, to describe the rationale and physiologic basis of their utility, to describe our experience in managing these cases, to present some of our results, and finally, to show the clinical utility of these techniques in the intraoperative management of CVDs.

    View details for Web of Science ID 000264960000006

    View details for PubMedID 19279496

  • Visual field preservation after curative multi-modality treatment of occipital lobe artemovenous malformations NEUROSURGERY Sinclair, J., Marks, M. P., Levy, R. P., Adler, J. R., Chang, S. D., Lopez, J. R., Do, H. M., Bell-Stephens, T. E., Lim, M., Steinberg, G. K. 2005; 57 (4): 655-666


    Occipital lobe arteriovenous malformations (AVMs) provide challenging management decisions because of their proximity to the visual cortex and optic radiations. Preservation of visual function throughout treatment is the mainstay of therapeutic planning. We reviewed visual field (VF) outcomes of all patients who received curative treatment for occipital AVMs at Stanford University to evaluate the efficacy of different treatment strategies.We conducted a retrospective review of 55 patients with occipital AVMs treated at Stanford University between 1984 and 2003. Clinical presentation, AVM morphology, and treatment modality were correlated with VF function before and after therapeutic intervention.Of 55 patients, 48 (87.3%) underwent multimodality AVM treatment (7 patients < 3 yr from radiosurgery were excluded from final analysis). One patient died from intracerebral hemorrhage 11 months post-radiosurgery, and five patients deferred further treatment. Forty-two patients (87.5%) were cured, with no residual AVM on final angiography. Curative therapeutic modalities used included embolization alone (2 patients), microsurgery alone (6 patients), microsurgery with radiosurgery (1 patient), microsurgery with embolization (23 patients), radiosurgery with embolization (4 patients), and embolization with radiosurgery and microsurgery (6 patients). Mean follow-up was 5.8 years including treatment. VF follow-up was available in all 42 patients. Twenty-eight (66.7%) patients experienced no change in VFs, six (14.3%) patients with previously abnormal VFs improved, and eight (19.0%) patients showed worsening of VFs (although none developed a new homonymous VF deficit). Duration of treatment was related to VF outcome in patients who presented without a history of AVM-related hemorrhage.Occipital AVMs can be safely cured using multimodality strategies with minimal risk to visual function despite the proximity of these lesions to the visual cortex and associated pathways.

    View details for DOI 10.1227/01.NEU.0000175547.05291.85

    View details for Web of Science ID 000236681500018

    View details for PubMedID 16239877

  • Wrist hyperextension leads to median nerve conduction block - Implications for intra-arterial catheter placement ANESTHESIOLOGY Chowet, A. L., Lopez, J. R., Brock-Utne, J. G., Jaffe, R. A. 2004; 100 (2): 287-291


    It is common practice to hyperextend the wrist to facilitate insertion of a radial intra-arterial catheter. This position may be maintained for prolonged periods. Although there has been much discussion about optimal patient management to protect the ulnar nerve and brachial plexus, little attention has been paid to the median nerve during wrist hyperextension. The authors report the effects of wrist hyperextension on conduction in the median nerve.Median nerve conduction was studied in 12 awake, healthy volunteers using standard nerve conduction tests consisting of the measurement of compound sensory and motor action potentials, as well as their amplitudes and latencies. With the contralateral hand as a control, the right wrist was placed in hyperextension (angled between 65 and 80 degrees), and compound action potentials were recorded to determine the onset and magnitude of effects. Subsequently, the hand was released from hyperextension and recovery was recorded.In 83% of subjects, hyperextension resulted in a significant decrease in compound sensory action potential amplitudes, sufficient to qualify as conduction block (16.6% of baseline). The average time to conduction block was 43 +/- 13.2 min. All subjects who manifested conduction block showed marked improvement 5 min after release from hyperextension.Wrist hyperextension for arterial line placement and stabilization is likely to result in profound impairment of median nerve function. Although the effects were transient in this study, the results suggest that prolonged hyperextension may be associated with significant changes in median nerve conduction. To minimize the chance for nerve injury, the authors recommend that wrists be returned promptly to the neutral position following arterial line placement.

    View details for Web of Science ID 000188438500015

    View details for PubMedID 14739802

  • The use of evoked potentials in intraoperative neurophysiologic monitoring. Physical medicine and rehabilitation clinics of North America López, J. R. 2004; 15 (1): 63-84


    Although not universally adopted, the growing body of literature provides strong evidence of the clinical utility of IOM in a variety of cerebrovascular surgical and endovascular procedures. The Therapeutics and Technology Subcommittee of the American Academy of Neurology and Fisher et al concluded that the following are useful and noninvestigational: 1. EEG, compressed spectral array, and SSEP in CEA and brain surgeries that potentially compromise cerebral blood flow, 2. BAEP and cranial nerve monitoring in surgeries performed in the region of the brainstem or inner ear, 3. SSEP monitoring performed for surgical procedures potentially involving ischemia or mechanical trauma of the spinal cord. They also came to the conclusion that although promising, motor EPs and visual EPs are still investigational. Further investigation, especially in the area of outcomes research and cost-effectiveness, is required before IOM can become standard practice.

    View details for PubMedID 15029899

  • Neurophysiological monitoring in the endovascular therapy of aneurysms AMERICAN JOURNAL OF NEURORADIOLOGY Liu, A. Y., Lopez, J. R., Do, H. M., Steinberg, G. K., Cockroft, K., Marks, M. P. 2003; 24 (8): 1520-1527


    Endovascular aneurysm therapy has associated risks of ischemic complications. We undertook this study to evaluate the efficacy of neurophysiological monitoring (NPM) techniques in the detection of ischemic changes that may be seen during endovascular treatment of cerebral aneurysms.Thirty-five patients underwent NPM during endovascular treatment of cerebral aneurysms. The patients underwent a total of 50 endovascular procedures, including balloon test occlusion (19 patients), GDC embolization (22 patients), and permanent vessel occlusion (nine patients). NPM included electroencephalography, somatosensory evoked potentials, and/or brain stem auditory evoked potentials, depending on the location of the aneurysm.NPM changes were seen in nine (26%) of 35 patients and altered the management in five (14%) of 35 patients. In three of the five cases, NPM changes were observed without corresponding neurologic physical examination changes after balloon test occlusion (performed while the patients were under general anesthesia in two cases). In the two other cases in which NPM changes altered management, ischemia was detected at the time of intra-aneurysmal therapy while the patients were under general anesthesia. Overall, 18 of 35 patients underwent a total of 19 balloon test occlusion procedures. Of the 17 remaining patients, 13 underwent aneurysm coiling, two were not treated because of inability to safely place coils, and two were treated for distal aneurysms. Two patients developed transient neurologic deficits without concurrent NPM changes, representing false-negative NPM test results.NPM is a valuable adjunct to endovascular treatment of cerebral aneurysms. Our study suggests that these monitoring techniques may reduce ischemic complications and can be used to help guide therapeutic decisions.

    View details for Web of Science ID 000185400100007

    View details for PubMedID 13679263

  • Hyperperfusion syndrome with hemorrhage after angioplasty for middle cerebral artery stenosis AMERICAN JOURNAL OF NEURORADIOLOGY Liu, A. Y., Do, H. M., Albers, G. W., Lopez, J. R., Steinberg, G. K., Marks, M. P. 2001; 22 (8): 1597-1601


    Hyperperfusion syndrome is a well-documented complication of carotid endarterectomy, as well as internal carotid artery angioplasty and stent placement. We report a similar complication after distal intracranial (middle cerebral artery [MCA] M2 segment) angioplasty. To our knowledge, this is the first report of hyperperfusion syndrome after intracranial angioplasty of a distal MCA branch.

    View details for Web of Science ID 000171119500028

    View details for PubMedID 11559514

  • Microsurgical resection of brainstem, thalamic, and basal ganglia angiographically occult vascular malformations NEUROSURGERY Steinberg, G. K., Chang, S. D., Gewirtz, R. J., Lopez, J. R. 2000; 46 (2): 260-270


    To evaluate the clinical results for patients who underwent resection of angiographically occult vascular malformations (AOVMs) of the brainstem, thalamus, or basal ganglia, successfully resected after it exhibited rebleeding and presented to a pial surface.Between January 1990 and May 1998, 56 patients with 57 deep AOVMs underwent 63 operations, at Stanford University Medical Center, to treat AOVMs of the brainstem (42 AOVMs), thalamus (5 AOVMs), or basal ganglia (10 AOVMs). The surgical approach was suboccipital midline (27 operations), far lateral suboccipital (10 operations), transsylvian (9 operations), interhemispheric transcallosal or infracallosal (8 operations), infratentorial supracerebellar (6 operations), or subtemporal (3 operations). Four patients experienced recurrent bleeding from the same lesion after surgical resection, requiring a second operation. One patient required a planned second operation, using a different approach, to completely resect the lesion, and one patient underwent two surgical procedures to resect two separate brainstem AOVMs. One patient initially underwent exploration but not resection of her AOVM, because it did not present to a pial or ependymal surface. The AOVM was successfully resected after it exhibited rebleeding and presented to a pial surface.The immediate outcomes after surgery were unchanged for 31 patients (55%), worsened for 16 (29%), and improved for 9 (16%). The long-term outcomes were unchanged for 24 patients (43%), compared with their presenting grade, worse for 3 (5%), and improved for 29 (52%). Patients who had undergone previous radiotherapy or radiosurgery to treat these lesions experienced more difficult postoperative courses, and radiation necrosis was observed for two patients.AOVMs of the brainstem, thalamus, and basal ganglia can be safely removed, with a long-term neurological morbidity rate of only 5% and a complete lesion resection rate of 93% after the initial planned resection. The use of cranial base surgical approaches and intraoperative electrophysiological monitoring contributes to successful clinical outcomes.

    View details for Web of Science ID 000085191800002

    View details for PubMedID 10690715

  • AAEM news and comments Muscle & nerve Chang, S. D., Lopez, J. R., Steinberg, G. K. 2000; 23 (9): 1450-1

    View details for PubMedID 10951454

  • Reply Muscle & nerve Chang, S. D., Lopez, J. R., Steinberg, G. K. 2000; 23 (9): 1446

    View details for PubMedID 10951453

  • Intraoperative electrical stimulation for identification of cranial nerve nuclei Chang, S. D., Lopez, J. R., Steinberg, G. K. JOHN WILEY & SONS INC. 1999: 1538-1543


    The purpose of this study was to evaluate the feasibility and usefulness of cranial nerve nuclei monitoring during resection of brainstem cavernous malformations. Eleven patients with brainstem cavernous malformations underwent resection of their malformations utilizing cranial nerve nuclei monitoring. Cranial nerves V and VII were monitored by placing electrodes in muscle groups innervated by these nerves and recording manipulation-induced neurotonic discharges and triggered electromyographic (EMG) activity, after electrical stimulation of the corresponding brainstem nuclei. Seven of 11 procedures (64%) with cranial nerve nuclei monitoring were noted to have cranial nerve nuclei activity corresponding to manipulation of the nuclei. The cavernous malformation was completely resected in 5 of 7 cases with cranial nerve nuclei activity and in all 4 cases without activity. In the remaining 2 cases, the cavernous malformation was not resected due to the proximity of the monitored cranial nerve nuclei to the cavernous malformation and to increasing neurotonic activity as the cavernous malformation was approached. None of the 11 patients had new permanent postoperative deficits corresponding to the cranial nerve nuclei monitored; 1 patient had a transient partial facial palsy lasting 2 days. Preliminary results indicate that cranial nerve nuclei monitoring proves useful in preserving neurologic function and reducing surgical morbidity during resection of brainstem cavernous malformations, particularly indicating when lesion resection places these nuclei at risk.

    View details for Web of Science ID 000083306000008

    View details for PubMedID 10514231

  • The usefulness of electrophysiological monitoring during resection of central nervous system vascular malformations. Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association Chang, S. D., Lopez, J. R., Steinberg, G. K. 1999; 8 (6): 412-422


    Goal: The purpose of this study was to evaluate the usefulness of electrophysiological monitoring during the resection of vascular malformations. Methods: Between September 1994 and April 1996, we surgically resected vascular malformations (31 arteriovenous malformations, 22 angiographically occult vascular malformations) from 53 patients (56 procedures) and used intraoperative evoked potential monitoring. Somatosensory evoked potentials (SSEPs) were monitored in 54 procedures (96%), and brain stem auditory evoked potentials (BAEPs) in 17 (30%). The neurological status of the patients was evaluated before and after surgery. Findings: Five of the 54 patients (9%) monitored with SSEPs had SSEP changes (4 transient, 1 persistent) coinciding with new clinical neurological deficits in 4 patients (all transient). In all 4 patients who had transient SSEP changes, the changes resolved with adjustment or removal of clips on feeding vessels (2 patients) or with elevating mean arterial pressure (MAP) (2 patients). Forty-seven patients (91%) had neither SSEP or neurological examination alterations. One of 17 patients (6%) monitored with BAEPs had neurological and persistent BAEP changes, 15 (88%) had neither BAEP or neurological changes, and 1 (6%) had a neurological change despite no change in BAEP (false negative). The sensitivity of SSEP and BAEP for predicting a new postoperative deficit (transient or prolonged) in this series was 86% (6/7); specificity was 98% (55/56). Clinical outcome was excellent in 41 patients, good in 11 and poor in 1 (no patients died) and was largely related to pretreatment grade. Conclusion: SSEPs and BAEPs predict the likelihood of clinical neurological injury during resection of vascular malformations with high sensitivity and specificity and may prove a useful adjunct in treating these lesions.

    View details for PubMedID 17895195

  • Embolization of rolandic cortex arteriovenous malformations NEUROSURGERY Paulsen, R. D., Steinberg, G. K., Norbash, A. M., Marcellus, M. L., Lopez, J. R., Marks, M. P. 1999; 44 (3): 479-484


    To evaluate the safety and efficacy of preradiosurgical and presurgical embolization of arteriovenous malformations (AVMs) involving the rolandic cortex.Seventeen consecutive patients with rolandic AVMs seen during a 31-month period (December 1994-July 1997) were evaluated. All patients underwent superselective sodium amobarbital testing to determine any changes in the results of the neurological examinations before undergoing embolization. In 16 of 17 patients (94.1%), somatosensory evoked potentials augmented physical examinations. Patients were embolized with N-butyl cyanoacrylate (Histoacryl; B. Braun, Melsungen, Germany) and iophendylate (Ethiodol; Savage Labs, Melville, NY). Rigid control of the mean arterial pressure (65-75 mm Hg) was maintained in all patients for 24 to 48 hours after embolization.Twenty-three embolization sessions were performed in 17 patients (mean, 1.5 sessions/patient), and a total of 40 feeding arteries were embolized. Two patients were unable to undergo embolization because of positive results of the amobarbital testing despite repeated attempts to reposition a microcatheter in the AVM circulation. In one case, somatosensory evoked potentials and the results of the physical examination were both positive; in the other case, only the somatosensory evoked potentials were used (in a pediatric patient under general anesthesia). All patients with AVMs that were embolized experienced a significant size reduction of their lesions (range, 20-95%; mean, 63%). There were no permanent complications. Four procedures (10% of the procedures, 23% of the patients) resulted in minor transient neurological deficits, with patients' conditions returning to baseline. Thirteen patients subsequently underwent radiosurgery, three underwent surgical resection, and one underwent combined surgery and radiosurgery. Complete obliteration of the lesions has been achieved in four patients to date (three who underwent surgery and one who underwent radiosurgery), with the remainder undergoing further follow-up.When properly evaluated before treatment, rolandic AVMs can be embolized with a high success rate (measured by completed embolization and size reduction) and a low complication rate.

    View details for Web of Science ID 000078716500020

    View details for PubMedID 10069584

  • The use of electrophysiological monitoring in the intraoperative management of intracranial aneurysms JOURNAL OF NEUROLOGY NEUROSURGERY AND PSYCHIATRY Lopez, J. R., Chang, S. D., Steinberg, G. K. 1999; 66 (2): 189-196


    Somatosensory evoked potentials (SSEPs) and brainstem auditory evoked potentials (BAEPs) have been increasingly utilised during surgery for intracranial aneurysms to identify cerebral ischaemia. Between July 1994 and April 1996, we surgically treated 70 aneurysms in 49 consecutive patients (58 operations) with the aid of intraoperative evoked potential monitoring. This study sought to evaluate the usefulness of SSEP and BAEP monitoring during intracranial aneurysm surgery.Mean patient age was 51.9 (range 18-79) years. The sizes of the aneurysms were 3-4 mm (15), 5-9 mm (26), 10-14 mm (11), 15-19 mm (seven), 20-24 mm (six), and >25 mm (five). SSEPs were monitored in 58 procedures (100%) and BAEPs in 15 (26%). The neurological status of the patients was evaluated before and after surgery.Thirteen of the 58 procedures (22%) monitored with SSEPs had SSEP changes (12 transient, one persistent); 45 (78%) had no SSEP changes. Three of 15 patients (20%) monitored with BAEPs had changes (two transient, one persistent); 12 (80%) had no BAEP changes. Of the 14 patients with transient SSEP or BAEP changes, these changes resolved with adjustment or removal of aneurysm clips (nine), elevating MAP (four), or retractor adjustment (one). Mean time from precipitating event to electrophysiological change was 8.9 minutes (range 3-32), and the mean time for recovery of potentials in patients with transient changes was 20.2 minutes (range 3-60). Clinical outcome was excellent in 39 patients, good in five, and poor in three (two patients died), and was largely related to pretreatment grade.SSEPs and BAEPs are useful in preventing clinical neurological injury during surgery for intracranial aneurysms and in predicting which patients will have unfavourable outcomes.

    View details for Web of Science ID 000078450800011

    View details for PubMedID 10071098

  • Evoked potential monitoring and EKG: A case of a serious "cardiac arrhythmia" ANESTHESIOLOGY Diachun, C. A., Brock-Utne, J. G., Lopez, J. R., Ceranski, J. A. 1998; 89 (5): 1270-1272

    View details for Web of Science ID 000076891400033

    View details for PubMedID 9822022

  • Intraoperative neurophysiological monitoring INTERNATIONAL ANESTHESIOLOGY CLINICS Lopez, J. R. 1996; 34 (4): 33-54

    View details for Web of Science ID A1996VV64300004

    View details for PubMedID 8956063

  • ENTOMOPIA - A REMARKABLE CASE OF CEREBRAL POLYOPIA NEUROLOGY Lopez, J. R., Adornato, B. T., Hoyt, W. F. 1993; 43 (10): 2145-2146

    View details for Web of Science ID A1993MC70400055

    View details for PubMedID 8413985