Coverage Policy Manual
Policy #: 1998095
Category: Surgery
Initiated: February 1998
Last Review: September 2018
  Intraoperative Neurophysiologic Monitoring

Description:
Intra-operative neurophysiologic monitoring describes a variety of procedures that have been used to monitor the integrity of neural pathways during high-risk neurosurgical, orthopedic, and vascular surgeries. The principal goal of intra-operative monitoring is the identification of nervous system impairment in the hope that prompt intervention will prevent permanent deficits. Correctable factors at surgery include circulatory disturbance, excess compression from retraction, bony structures, or hematomas, or mechanical stretching. The various different methodologies of monitoring are described below:
 
Sensory-evoked Potentials
Sensory-evoked potential describes the responses of the sensory pathways to sensory or electrical stimuli. Intra-operative monitoring of sensory-evoked potentials is used to assess the functional integrity of central nervous system (CNS) pathways during operations that put the spinal cord or brain at risk for significant ischemia or traumatic injury. The basic principles of sensory-evoked potential monitoring involve identification of a neurological region at risk, selection and stimulation of a nerve that carries a signal through the at-risk region, and recording and interpretation of the signal at certain standardized points along the pathway. Monitoring of sensory-evoked potentials is commonly used during the following procedures: carotid endarterectomy, brain surgery involving vasculature, surgery with distraction compression or ischemia of the spinal cord and brainstem, and acoustic neuroma surgery. Sensory-evoked potentials can be further broken down into the following categories according to the type of simulation used:
    • Somatosensory-evoked potentials (SSEPs) are electrical waves that are  generated by the response of sensory neurons to stimulation. Peripheral  nerves, such as the median, ulnar, or tibial nerve are typically stimulated but  in some situations the spinal cord may be stimulated directly. Recording is done either cortically or at the level of the spinal cord above the surgical procedure. Intra-operative monitoring of SSEPs is most commonly used during orthopedic or neurologic surgery to prompt intervention to reduce surgically induced morbidity and/or to monitor the level of anesthesia. One of the most common indications for SSEP monitoring is in patients undergoing corrective surgery for scoliosis. In this setting, SSEP monitors the status of the posterior column pathways, and thus does not reflect ischemia in the anterior (motor) pathways. Several different techniques are commonly used, including stimulation of a relevant peripheral nerve with monitoring from the scalp, from interspinous ligament needle electrodes, or from catheter electrodes in the epidural space.
    • Brainstem auditory-evoked potentials (BAEPs) are generated in response to auditory clicks and can define the functional status of the auditory nerve. Surgical resection of a cerebellopontine angle tumor, such as an acoustic neuroma, places the auditory nerves at risk, and BAEPs have been extensively used to monitor auditory function during these procedures.
    • Visual-evoked potentials (VEPs) are used to track visual signals from the retina to the occipital cortex light flashes. VEP monitoring has been used for surgery on lesions near the optic chiasm. However, VEPs are very difficult to interpret due to their sensitivity to anesthesia, temperature, and blood pressure.
 
EMG (Electromyogram) Monitoring and Nerve Conduction Velocity Measurements
Electromyogram monitoring and nerve conduction velocity measurements can be performed in the operating room and may be used to assess the status of the peripheral nerves, e.g., to identify the extent of nerve damage prior to nerve grafting or during resection of tumors. In addition, these techniques may be used during procedures around the nerve roots and around peripheral nerves to assess the presence of excessive traction or other impairment. Surgery in the region of cranial nerves can be monitored by electrically stimulating the proximal (brain) end of the nerve and recording via EMG in the facial or neck muscles. Thus monitoring is done in the direction opposite that of sensory-evoked potentials, but the purpose is similar — to verify that the neural pathway is intact.
 
Motor-Evoked Potential Monitoring
Motor-evoked potentials are recorded from muscles following direct or transcranial electrical stimulation of motor cortex or by pulsed magnetic stimulation provided by a coil placed over the head. Stimulation induces an electrical current in the brain or spinal cord which in turn can stimulate the motor neurons. Muscle activity is recorded by electrodes placed on the skin at prescribed points along the motor pathways. Motor evoked potentials, especially when induced by magnetic stimulation, can be affected by anesthesia. The Digitimer electrical cortical stimulator received FDA premarket approval in 2002. Devices for transcranial magnetic stimulation have not yet received approval from the U.S. Food and Drug Administration (FDA) for this use.
 
 
EEG (Electroencephalogram) Monitoring
Spontaneous EEG monitoring can also be recorded during surgery and can be subdivided as follows:
    • EEG monitoring has been widely used to monitor cerebral ischemia secondary to carotid cross clamping during a carotid endarterectomy. EEG monitoring may identify those patients who would benefit from the use of a vascular shunt during the procedure to restore adequate cerebral perfusion. Conversely, shunts, which have an associated risk of iatrogenic complications, may be avoided in those patients in whom the EEG is normal. Carotid endarterectomy may be done with the patient under local anesthesia so that monitoring of cortical function can be directly assessed.
    • Electrocorticography (Cog) is the recording of the EEG directly from a surgically exposed cerebral cortex. Cog is typically used to define the sensory cortex and to map the critical limits of a surgical resection. ECoG recordings have been most frequently used to identify epileptogenic regions for resection. In these applications, electrocorticography does not constitute monitoring per se.

Policy/
Coverage:
Effective April 2019
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Intraoperative monitoring is considered reimbursable as a separate service only when a licensed physician, other than the operating surgeon or performing anesthesiologists, performs the monitoring while in attendance in the operating room throughout the procedure or from outside the operating room (remote or nearby), per patient, [attention directed exclusively to one patient (one on one monitoring)].
 
Intraoperative monitoring which includes somatosensory-evoked potentials, motor-evoked potentials using transcranial electrical stimulation, brainstem auditory-evoked potentials, EMG of cranial nerves, EEG, and electrocorticography (ECoG), meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes during spinal, intracranial, or vascular procedures.
 
NOTE: Intraoperative monitoring typically is done in the operating room (OR) by a technician, with a physician as a remote backup. In some operating rooms there is a central physician monitoring room, where a physician may simultaneously monitor several cases.
 
Intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes in patients undergoing:
    • high-risk thyroid or parathyroid surgery, including:  
            • total thyroidectomy  
            • repeat thyroid or parathyroid surgery  
            • surgery for cancer  
            • thyrotoxicosis  
            • retrosternal or giant goiter  
            • thyroiditis  
    • anterior cervical spine surgery associated with any of the following increased risk situations:
            • prior anterior cervical surgery, particularly revision anterior cervical discectomy and fusion, revision surgery through a scarred surgical field, reoperation for pseudarthrosis or revision for failed fusion  
            • multilevel anterior cervical discectomy and fusion  
            • preexisting recurrent laryngeal nerve pathology, when there is residual function of the recurrent laryngeal nerve.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve during anterior cervical spine surgery not meeting the criteria above or during esophageal surgeries does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve during anterior cervical spine surgery not meeting the criteria above or during esophageal surgeries is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Intraoperative monitoring of visual-evoked potentials and intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intraoperative monitoring of visual-evoked potentials is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Due to the lack of FDA approval, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, Intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Effective Prior to April 2019
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage
Criteria
 
Intraoperative monitoring is considered reimbursable as a separate service only when a licensed physician, other than the operating surgeon or performing anesthesiologists, performs the monitoring while in attendance in the operating room throughout the procedure.
 
Intraoperative monitoring which includes somatosensory-evoked potentials, motor-evoked potentials using transcranial electrical stimulation, brainstem auditory-evoked potentials, EMG of cranial nerves,
EEG, and electrocorticography (ECoG), meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes during spinal, intracranial, or vascular procedures.
 
NOTE: Intraoperative monitoring typically is done in the operating room (OR) by a technician, with a physician as a remote backup. In some operating rooms there is a central physician monitoring room, where a physician may simultaneously monitor several cases.
 
Intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes in patients undergoing:
  • high-risk thyroid or parathyroid surgery, including:
      • total thyroidectomy
      • repeat thyroid or parathyroid surgery
      • surgery for cancer
      • thyrotoxicosis
      • retrosternal or giant goiter
      • thyroiditis
  • anterior cervical spine surgery associated with any of the following increased risk situations:
      • prior anterior cervical surgery, particularly revision anterior cervical discectomy and fusion, revision surgery through a scarred surgical field, reoperation for pseudarthrosis or revision for failed fusion
      • multilevel anterior cervical discectomy and fusion
preexisting recurrent laryngeal nerve pathology, when there is residual function of the recurrent laryngeal nerve.
 
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary
Coverage Criteria
 
Intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve during anterior cervical spine surgery not meeting the criteria above or during esophageal surgeries does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intraoperative neurophysiologic monitoring of the recurrent laryngeal nerve during anterior cervical spine surgery not meeting the criteria above or during esophageal surgeries is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Intraoperative monitoring of visual-evoked potentials and intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intraoperative monitoring of visual-evoked potentials is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Due to the lack of FDA approval, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, Intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Effective Prior to August 2017
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Intraoperative monitoring is considered reimbursable as a separate service only when a licensed physician, other than the operating surgeon or performing anesthesiologists, performs the monitoring while in attendance in the operating room throughout the procedure.
 
Intraoperative monitoring which includes somatosensory-evoked potentials, motor-evoked potentials using transcranial electrical stimulation, brainstem auditory-evoked potentials, EMG of cranial nerves, EEG, and electrocorticography (ECoG), meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes during spinal, intracranial, or vascular procedures.
 
NOTE: Intraoperative monitoring typically is done in the operating room (OR) by a technician, with a physician as a remote backup. In some operating rooms there is a central physician monitoring room, where a physician may simultaneously monitor several cases.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Intraoperative monitoring of visual-evoked potentials and intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intraoperative monitoring of visual-evoked potentials is considered investigational.  Investigational services are exclusions in the member benefit certificate of coverage.
 
Due to the lack of FDA approval, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For contracts without primary coverage criteria, intra-operative monitoring of motor-evoked potentials using transcranial magnetic stimulation is considered investigational. Investigational services are exclusions in the member benefit certificate of coverage.
 
Effective prior to May 2011
Intraoperative monitoring which includes somatosensory-evoked potentials, brainstem auditory-evoked potentials, EMG of cranial nerves, EEG, and electrocorticography (ECoG), meet primary coverage criteria for effectiveness and are covered during spinal, intracranial, or vascular procedures.
 
Intraoperative monitoring typically is done in the operating room (OR) by a technician, with a physician as a remote backup. In some operating rooms there is a central physician monitoring room, where a physician may simultaneously monitor several cases.
 
Intraoperative monitoring is considered reimbursable as a separate service only when a licensed physician, other than the operating surgeon or performing anesthesiologists, performs the monitoring while in attendance in the operating room throughout the procedure.
 
Intraoperative monitoring of visual-evoked potentials and intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves is not covered based on benefit certificate primary coverage criteria that there be scientific evidence of effectiveness.
 
For contracts without primary coverage criteria, intraoperative monitoring of visual-evoked potentials is considered investigational.  Investigational services are an exclusion in the member certificate of coverage.
 
For contracts without primary coverage criteria, intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves is considered not medically necessary.  Medically unnecessary services are an exclusion in the member certificate of coverage.

Rationale:
At the present time, intra-operative monitoring of neurologic function is a widely diffused practice, particularly during cervical and thoracic spinal surgery. There have been several references that have looked at the efficacy of this technology and the controversies surrounding its use.  A literature search through March 2004, which again revealed that intraoperative monitoring is a widely accepted practice without a strong evidence-based support through controlled trials.
 
2007 Update
There continues to be controversy about the type of intraoperative monitoring and under what circumstances it might be appropriate despite the fact that it is widely used.
 
Resnick and colleagues concluded: "Based on the medical evidence provided by the literature reviewed, there does not appear to be support for the hypothesis that any form of intraoperative monitoring improves patient outcomes following lumbar decompression or fusion procedures for degenerative spinal disease."  "There is no substantial evidence to indicate that the use of intraoperative monitoring of any kind provides useful information to the surgeon in terms of assessing the adequacy of nerve root compression at the time of surgery."
 
2011 Update
This policy was updated with a search of the MEDLINE database from through January 2011 focusing on intraoperative evoked potentials that had previously not met primary coverage criteria or had been considered investigational. It appears that monitoring of motor-evoked potentials, particularly for spine surgery and open abdominal aorta aneurysm repairs, has broad acceptance although the evidence base consists mainly of observational studies. There is ongoing controversy about its utility in some surgical procedures.
 
Most of the literature is from Europe and the United Kingdom and, while many papers report the sensitivity and specificity of motor evoked potentials for predicting post-surgical neurological deficits, few papers report intraoperative interventions undertaken in response to information from monitoring. Authors of a study from a U.S. center reviewed records of 1121 patients with scoliosis treated at 4 pediatric spine centers between 2000 and 2004 and monitored with a multimodality technique (Schwartz, 2007). Thirty-eight had recordings that met criteria for signal change. Of these, 17 showed suppression of the amplitude of transcranial electrical motor evoked potentials in excess of 65% without evidence of changes in somatosensory evoked potentials. In 9 of the 38 patients, the signal change was related to hypotension and was corrected with augmentation of the blood pressure. In the remaining 29 patients, the alert was related directly to a surgical maneuver (segmental vessel clamping and posterior instrumentation and correction). Nine of the 26 patients with an instrumentation related alert woke with a transient motor and/or sensory deficit. Seven of these 9 patients presented solely with a motor deficit, which was detected by monitoring of motor evoked potentials in all cases. Two patients had only sensory symptoms. SEPs failed to identify a motor deficit 4 of the 7 patients and, when changes in sensory-evoked potentials (SEPs) occurred, they lagged behind changes in transcranial electric motor evoked potentials by an average of approximately 5 minutes. In a review, Malhotra and Shaffrey note that although motor evoked potential monitoring is considered to be safe, relative contraindications include epilepsy, cortical lesion, skull defect, proconvulsant medication, cardiac pacing and implantable device (Malhotra, 2010).  
 
Several articles from Asia describe potentially useful methods of utilizing intraoperative visual evoked potentials to assess the integrity of visual pathway structures including optic nerves in order to detect visual impairment before it is irreversible (Sasaki, 2010) (Ota, 2010). More research is required to identify the role and utility of intraoperative visual invoked potentials.
 
Guidelines
Recommended Standards for Neurophysiologic Intraoperative Monitoring (NIOM) were published in 2009 by American Clinical Neurophysiology Society. Guideline 11A includes the following statement. The monitoring team should be under the direct supervision of a physician with training and experience in NIOM. The monitoring physician should be licensed in the state and privileged to interpret neurophysiologic testing in the hospital in which the surgery is being performed. He/she is responsible for real-time interpretation of NIOM data. The monitoring physician should be present in the operating room or have access to NIOM data in real-time from a remote location and be in communication with the staff in the operating room. There are many methods of remote monitoring, however any method used must conform to local and national protected health information guidelines. The monitoring physician must be available to be in the operating room, and the specifics of this availability (i.e., types of surgeries) should be decided by the hospital credentialing committee. In order to devote the needed attention, it is recommended that the monitoring physician interpret no more than three cases concurrently.
 
The coverage statement is being changed to indicate motor-evoked potentials using transcranial electrical stimulation meets primary coverage criteria and due to the lack of FDA approval motor-evoked potential using transcranial magnetic stimulation does not meet primary coverage criteria.
 
2014 Update
This policy is updated with a literature search through December 2013. Two case series and a position statement were identified but there was no new literature identified that would prompt a change in the coverage statement.
 
A few small case series of neurophysiologic monitoring of peripheral nerves in patients undergoing orthopedic procedures including tibial/fibular osteotomies and hip arthroscopy for femoroacetabular impingement were identified (Ochs, 2012; Jahangiri, 2013).
 
The ASNM 2013 position statement on intraoperative motor evoked potential monitoring includes the statement that MEPs are an established practice option for cortical and subcortical mapping and for monitoring during surgeries risking motor injury in the brain, brainstem, spinal cord or facial nerve (Macdonald, 2013).
  
2015 Update
A literature search conducted through April 2014 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
In a 2011 report, Clarkson et al describe the use of intraoperative nerve recording for suspected brachial plexus root avulsion (Clarkson, 2011). Included in this retrospective review were 25 consecutive patients who underwent intraoperative nerve recording during surgery for unilateral brachial plexus injury. Of 55 roots thought to be avulsed preoperatively, 14 (25%) were found to be intact with intraoperative nerve recording. Eleven of these were then used for reconstruction, of which 9 (82%) had a positive functional outcome.
 
A correlation between specific EMG signals from motor cranial nerves and postoperative facial palsy was reported in a series of patients who underwent surgery on acoustic neuroma (n=24) or meningioma (n=6) (Romstock, 2000). During surgery, direct electrical stimulation was used to ensure that the nerve bundle remained intact. EMG was recorded from muscles targeted by the facial, trigeminal, and lower cranial nerves and analyzed off-line. The occurrence of the A train (a sinusoidal, symmetrical sequence of high-frequency and low-amplitude signals) was identified in 19 patients, of whom 18 had postoperative facial nerve paresis. With on false-positive and 3 false-negative measurements, sensitivity and specificity were calculated at 86% and 89%, respectively. Intervention was not performed during the surgery.
 
Neurophysiologic monitoring of peripheral nerves has also been reported in patients undergoing orthopedic procedures including tibial/fibular osteotomies, hip arthroscopy for femoroacetabular impingement, and shoulder arthroplasty (Ochs, 2012; Jahangiri, 2013; Nagda, 2007).
 
Clinical Input Received through Physician Specialty Societies and Academic Medical Centers
 
While the various physician specialty societies and academic medical centers may collaborate with and make recommendations during this process through the provision of appropriate reviewers, input received does not represent an endorsement or position statement by the physician specialty societies or academic medical centers, unless otherwise noted.
 
In response to requests, input was received from 5 physician specialty societies (7 responses) and 2 academic medical centers while this policy was under review in 2014. Input agreed that intraoperative monitoring with somatosensory-evoked potentials, motor-evoked potentials using transcranial electrical stimulation, brainstem auditory-evoked potentials, electromyogram (EMG) of cranial nerves, electroencephalogram (EEG), or electrocorticography (ECoG), may be medically necessary during spinal, intracranial, or vascular procedures. There was general agreement that intraoperative monitoring of visual-evoked potentials and motor-evoked potentials using transcranial magnetic stimulation is investigational. Input was mixed on whether intraoperative neurophysiological monitoring of peripheral nerves would be considered medically necessary. Some reviewers recommended monitoring of some peripheral nerves during spinal surgery (eg, nerve roots, percutaneous pedicle screw placement, lateral transpsoas approach to the lumbar spine). Other reviewers suggested neurophysiological monitoring for resection of peripheral nerve tumors or during surgery around the brachial plexus or facial/cranial nerves.
 
Practice Guidelines and Position Statements
 
A 2012 position statement on electrophysiological monitoring during routine spinal surgery by the American Association of Neurological Surgeons (AANS)/Congress of Neurological Surgeons (CNS) states that intraoperative electrophysiological monitoring during spinal surgery may assist in diagnosing neurological injury (AANS, 2014). However, the AANS/CNS finds no evidence that such monitoring either 1) reduces the incidence of neurological injury or 2) mitigates the severity of it. The position of the
AANS/CNS is that routine use of intraoperative electrophysiological monitoring is neither warranted nor recommended, although intraoperative electrophysiological monitoring should be performed if the diagnostic information gained is of value, particularly in high risk cases such as deformity, gross instability, navigation through or around peripheral nerves, or intramedullary procedures.
 
A 2013 position statement on somatosensory evoked potentials (SEPs) from the American Association of
Neuromuscular & Electrodiagnostic Medicine (AANEM) states that intraoperative SEPs have demonstrated usefulness for monitoring of spinal cord, brainstem, and brain sensory tracts (ANEM, 2013). AANEM states that intraoperative SEP monitoring is indicated for selected spine surgeries in which there is a risk of additional nerve root or spinal cord injury. Indications for SEP monitoring may include, but are not limited to, complex, extensive, or lengthy procedures, and when mandated by hospital policy. However, intraoperative SEP monitoring may not be indicated for routine lumbar or cervical root decompression.
 
A 2005 guideline from the AANS/CNS on the performance of lumbar fusion for degenerative disease of the lumbar spine found insufficient evidence to recommend a treatment standard for intraoperative electrophysiological monitoring (ANNS/CNS, 2005). The AANS/CNS provided a guideline recommendation for use of intraoperative somatosensory evoked potential (SSEP) or dermatomal sensory evoked potential (DSEP) monitoring as an adjunct in those circumstances during instrumented lumbar spinal fusion procedures in which the surgeon desires immediate intraoperative information regarding the potential of a neurological injury. The occurrence of a postoperative neurological deficit is highly correlated with intraoperative changes in these monitoring modalities. An abnormal SSEP or DSEP during surgery, however, often does not correlate with a postoperative neurological injury because of a high false-positive rate. Intraoperative evoked EMG recording was recommended as an option during lumbar spinal fusion surgery in those situations in which the operating surgeon desires immediate information regarding the integrity of the pedicle wall, as a normal evoked EMG response is correlated with an intact pedicle wall. A normal evoked EMG response is highly predictive of the lack of a neurological injury. An abnormal EMG response during the surgical procedure may or may not be associated with a clinically significant injury.
 
The AAN published a model policy on principles of coding for intraoperative neurophysiologic monitoring (IOM) and testing in 2012 (AAN, 2012). The background section of this document provides the following information on the value of IOM in averting neural injuries during surgery:
 
  1. Value of EEG Monitoring in Carotid Surgery. Carotid occlusion, incident to carotid endarterectomies, poses a high risk for cerebral hemispheric injury. EEG monitoring is capable of detecting cerebral ischemia, a serious prelude to injury. Studies of continuous monitoring established the ability of EEG to correctly predict risks of postoperative deficits after a deliberate, but necessary, carotid occlusion as part of the surgical procedure. The surgeon can respond to adverse EEG events by raising blood pressure, implanting a shunt, adjusting a poorly functioning shunt, or performing other interventions.
  2.  Multicenter Data in Spinal Surgeries. An extensive multicenter study conducted in 1995 demonstrated that IOM using SEP reduced the risk of paraplegia by 60% in spinal surgeries. The incidence of false negative cases, wherein an operative complication occurred without having been detected by the monitoring procedure, was small: 0.06%.
  3. Technology Assessment of Monitoring in Spinal Surgeries. A technology assessment by the McGill University Health Center reviewed 11 studies and concluded that spinal IOM is capable of substantially reducing injury in surgeries that pose a risk to spinal cord integrity. It recommended combined SEP/MEP monitoring, under the presence or constant availability of a monitoring physician, for all cases of spinal surgery for which there is a risk of spinal cord injury.
  4. Value of Combined Motor and Sensory Monitoring. Numerous studies of post-surgical paraparesis and quadriparesis have shown that both SEP and MEP monitoring had predicted adverse outcomes in a timely fashion. The timing of the predictions allowed the surgeons the opportunity to intervene and prevent adverse outcomes. The two different techniques (SEP and MEP) monitor different spinal cord tracts. Sometimes, one of the techniques cannot be used for practical purposes, for anesthetic reasons, or because of pre-operative absence of signals in those pathways. Thus, the decision about which of these techniques to use needs to be tailored to the individual patient’s circumstances.
  5. Protecting the Spinal Cord from Ischemia during Aortic Procedures. Studies have shown that IOM accurately predicts risks for spinal cord ischemia associated with clamping the aorta or ligating segmental spinal arteries. IOM can assess whether the spinal cord is tolerating the degree of relative ischemia in these procedures. The surgeon can then respond by raising blood pressure, implanting a shunt, reimplanting segmental vessels, draining spinal fluid, or through other interventions.
  6. Value of EMG Monitoring. Selective posterior rhizotomy in cerebral palsy significantly reduces spasticity, increases range of motion, and improves functional skills. Electromyography during this procedure can assist in selecting specific dorsal roots to transect. EMG can also be used in peripheral nerve procedures that pose a risk of injuries to nerves.
  7. Value of Spinal Monitoring using SSEP and MEPs. According to a recent review of spinal monitoring using SSEP and MEPs by the Therapeutics and Technology Assessment Subcommittee of the AAN and the American Clinical Neurophysiology Society, IOM is established as effective to predict an increased risk of the adverse outcomes of paraparesis, paraplegia, and quadriplegia in spinal surgery (4 Class I and 7 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).
 
Limitations on Coverage
 
To derive optimal benefits from this technology it is incumbent on the IOM team to understand the limits of the technology, listed below.
  1. Use of Qualified Personnel IOM must be furnished by qualified personnel. For instance, the beneficial results of monitoring with SSEPs demonstrated by the 1995 multicenter study (Nuwer et al., 1995) showed fewer neurological deficits with experienced monitoring teams. While false positive events were significant in only 1% of cases, the negative predictive value for this technique was over 99%. Thus, absence of events during monitoring signifies and assures safety of the procedure. In general it is recommended that the monitoring team strive to optimize recording and interpreting conditions such that:
    • A well-trained, experienced technologist, present at the operating site, is recording and monitoring a single surgical case; and
    • A monitoring clinical neurophysiologist supervises the technologist.
2. Effects of the Depth of Anesthesia and Muscle Relaxation. The level of anesthesia may also significantly impact on the ability to interpret intraoperative studies; therefore, pre-operative planning and continuous communication between the anesthesiologist and the monitoring team is expected.AAN.com
3. Recording Conditions. It is also expected that a specifically trained technologist or non-physician monitorist, preferably with credentials from the American Board of Neurophysiologic Monitoring or the American Board of Registration of Electrodiagnostic Technologists (ABRET), will be in continuous attendance in the operating room, with either the physical or electronic capability for real-time communication with the supervising physician.
4. Monitoring Necessity. Intraoperative monitoring is not medically necessary in situations where historical data and current practices reveal no potential for damage to neural integrity during surgery. Monitoring under these circumstances will exceed the patient’s medical need (Social Security Act (Title XVIII); Medicare Benefit Policy Manual).
5. Communications. Monitoring may be performed from a remote site, as long as a well-trained technologist (see detail above) is in continuous attendance in the operating room, with either the physical or electronic ability for prompt real-time communication with the supervising monitoring physician.
6. Supervision Requirements. Different levels of physician supervision apply to different kinds of IOM procedures. Code 95940 supervision require continuous physician monitoring in the operating room (OR). Code 95941 supervision require continuous physician monitoring which can be provided online or in the operating room (OR).
 
The American Society of Neurophysiological Monitoring (ASNM) provides a 2013 practice guideline for the supervising professional on intraoperative neurophysiological monitoring. The ASNM 2013 position statement on intraoperative motor-evoked potential monitoring includes the statement that MEPs are an established practice option for cortical and subcortical mapping and for monitoring during surgeries risking motor injury in the brain, brainstem, spinal cord or facial nerve (MacDonald, 2013).
 
2008 Guidance from the United Kingdom’s National Institute for Health and Care Excellence (NICE) on intraoperative nerve monitoring during thyroid surgery finds no major safety concerns (NIE, 2008). In terms of efficacy, IONM may be helpful in performing more complex operations such as reoperative surgery and operations on large thyroid glands. Therefore, it may be used with normal arrangements for consent, audit and clinical governance.
  
2016 Update
A literature search conducted through January 2016 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Neurophysiologic Monitoring of Peripheral Nerves
Surgical guidance with peripheral intraoperative monitoring has been reported in case series and 1 case control study. Other case series have reported on the predictive ability of monitoring of peripheral nerves. No prospective comparative studies were identified that assessed whether outcomes are improved with neurophysiologic monitoring.
 
Intervention during surgery was addressed by Kneist and colleagues in a case-control study with 30 patients (Kneist, 2013a). In patients undergoing total mesorectal excision, impaired anorectal function was observed in 1 (7%) of 15 patients who had intraoperative monitoring compared with 6 (40%) of 15 without. Kneist and colleagues also reported on erectile function following low anterior rectal resection in a pilot study with 17 patients (Kneist, 2013b).  In this study, the combined intraoperative measurement of bladder and internal anal sphincter innervation was a strong predictor of postoperative erectile function. Neurophysiologic monitoring predicted postoperative erectile function with a sensitivity of 90%, specificity of 86%, positive predictive value of 90%, and negative predictive value of 86%. The possibility of intervention during surgery was not addressed.
 
Electrophysiologic monitoring has also been reported to guide selective rhizotomy for glossopharyngeal neuralgia in a series of 8 patients (Zhang, 2014).
 
Ongoing and Unpublished Clinical Trials
Some currently active trials that might influence this policy are listed beow:
 
Ongoing
(ONCT02187653) an industry sponsored or cosponsored trial. Spine Registry Exposure for: Lumbar and Cervical Surgery Utilizing IOM; planned enrollment 10,000; completion date December 2016.
 
(NCT02395146) Intra-operative Monitoring of the External Branch of the Superior Laryngeal Nerve (EBSLN) During Thyroid Surgery: Does it Improve Voice Preservation?; planned enrollment 60; completion date March 2017.
 
(NCT01585707) Continuous Intraoperative Monitoring of the Pelvic Autonomic Nerves During Total Mesorectal Excision (TME) for the Prevention of Urogenital and Anorectal Dysfunction in Patients With Rectal Cancer; planned enrollment 188; completion date December 2017.
 
(NCT01630785) Observation of Neurosurgical Interventions With Intraoperative Neurophysiological Monitoring IONM; planned enrollment 5,000; completion date December 2023.
 
A 2014 guideline update from AANS/CNS found no evidence that conflict with their previous recommendations for intraoperative monitoring for lumbar fusion (Sharan, 2014).  They found no evidence that intraoperative monitoring can prevent injury to the nerve roots. They found limited evidence that intraoperative monitoring can indicate a medial pedicle breach by a pedicle screw, but once a nerve root injury has taken place, changing the direction of the screw does not alter the outcome.
 
2017 Update
A literature search conducted through July 2017 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
INTRAOPERATIVE NEUROPHYSIOLOGIC MONITORING OF THE RLN DURING THYROID OR PARATHYROID SURGERY
In 2016, Pardal-Refoyo and Ochoa-Sangrador reported on a systematic review of RLN injury during total thyroidectomy with or without intraoperative neurophysiologic monitoring (IONM) (Pardal=Refoyo, 2016). Included were 1 large (n=1000) and 1 small (n=23) RCT and 52 case series (total N=30,922 patients) that estimated the risk to the RLN. Twenty-nine studies used RLN monitoring and 25 did not. The prevalence of bilateral laryngeal paralysis in patients who had RLN monitoring was lower (2.43%; 95% confidence interval [CI], 1.55% to 3.5%) compared to series that did not (5.18%; 95% CI 2.53 to 8.7%). The absolute risk reduction was 2.75%, with a number needed to treat of 364.13.
 
The largest RCT of RLN neuromonitoring for thyroid surgery was reported by Barczynski and colleagues (Barczynski, 2009). RLN monitoring was performed with electrodes on the vocal muscles through the cricothyroid ligament, which may not be the method currently used in the United States. In 500 patients who had thyroidectomy with only visual RLN identification, there were 38 cases of transient RLN injuries and 12 cases of permanent RLN injuries. In the 500 patients who had visualization plus RLN monitoring, there were 19 transient injuries and 8 permanent RLN injuries. The absolute risk reduction with the addition of RLN monitoring was 2.3% for RLN injury (p=0.007) and 1.9% for RLN paresis (p=0.011), with no significant difference in the prevalence of permanent RLN palsy (0.4%, p=NS). However, in high-risk patients, defined as those undergoing surgery for cancer, thyrotoxicosis, retrosternal or giant goiter, or thyroiditis, the prevalence of transient RLN paresis was 2.9% lower in in patients who had RLN monitoring (p=0.011) compared to those with visual identification only. In low-risk patients, there was no significant difference in RLN injury rates between monitoring and no monitoring. Notably, high-risk patients with prior thyroid or parathyroid surgery were excluded from this trial. A benefit of RLN monitoring was also shown in patients undergoing high-risk total thyroidectomy (Vasileiadis, 2016).
 
IONM OF THE RLN DURING CERVICAL SPINE SURGERY
For anterior cervical spine surgery, a qualitative systematic review by Tan and colleagues identified potential mechanisms for RLN injury including direct pressure on the nerve by the endotracheal tube, pinching of the nerve by the surgical retractor, overstretching of the RLN, and division of the vagus nerve (Tan, 2014). Reviewers reported that the major cause of vocal cord palsy was believed to be due direct pressure by the endotracheal tube. There was moderate evidence that monitoring the cuff pressure reduced the incidence of vocal cord palsy, but there was a paucity of trial data to recommend the routine use of electromyography (EMG). Risk factors associated with a higher rate of RLN injury were surgery at more than 3 levels and reoperation. There was poor evidence that there is an increase with the level of incision and extent of surgery (single vs multilevel) and duration of surgery.
 
A 2016 meta-analysis by Erwood and colleagues included 3 prospective cohort studies and 5 retrospective series (total N=238 patients) on RLN injury following revision anterior cervical discectomy and fusion (ACDF) (Erwood, 2016). RLN injury was defined as hoarseness or dysphagia, based either on patient report or by independent evaluation. Meta-analysis indicated a RLN injury rate of 14.1% overall (95% CI, 9.8% to 19.1%). Included in the meta-analysis was a cohort study with prospective evaluation and dysphagia as a primary outcome (Lee 2007). In this study, the rate of hoarseness and dysphagia was as high as 62% at 6 months and 27.7% at 24 months. A more recent prospective study that was included in the meta-analysis is by Chen and colleagues (Chen, 2014) who reported dysphagia in 7.9% of patients. However, dysphagia was not a primary outcome in this study. The meta-analysis found evidence of publication bias, suggesting that studies which found low rates of RLN damage may not have been reported.
 
The RLN is not observable during anterior cervical spine surgery, so the method of stimulating the RLN and monitoring the EMG activity of the vocal cord muscles is not feasible. Dimopoulis and colleagues measured spontaneous EMG activity with electrodes embedded in the wall of the endotracheal tube to evaluate whether this method could detect RLN injury (Dimopoulos, 2009). Of 298 patients undergoing ACDF, 14.4% showed spontaneous intraoperative EMG activity. Postoperative RLN injury was observed in 2.3% of patients, all of whom showed spontaneous EMG activity during surgery. The sensitivity of IONM to predict RLN injury was 100% and specificity was 87%. IONM had a positive predictive value of 16% and negative predictive value of 97%. Significantly increased EMG activity was reported for patients with previous surgical procedures, multilevel procedures, longer lasting surgery, and self-retained retractors. No studies have been identified that evaluated whether increased EMG activity would lead to interventions and reduce the incidence of RLN damage. Possible distraction of the surgeons with the spontaneous EMG activity was noted.
 
IONM OF THE RLN DURING ESOPHAGEAL SURGERY
One 2014 comparative study from Asia was identified on RLN monitoring during surgery for esophageal Cancer (Zhong, 2014). One hundred fifteen patients with esophageal cancer were enrolled in this prospective study. In 54 patients, the left RLN was found and underwent monitoring. In the remainder (n=61), the RLN was not located. No RLN injury was reported during surgery in either group, but 6 of 61 patients who did not receive monitoring had notable RLN injury identified postoperatively. It is unclear whether the difference in outcomes was due to monitoring or to the inability to identify the RLN during surgery.
 
ONGOING CLINICAL TRIALS
Some currently unpublished trials that might influence this review are listed below:
 
Ongoing:
(NCT02395146) Intra-operative Monitoring of the External Branch of the Superior Laryngeal Nerve (EBSLN) During Thyroid Surgery: Does it Improve Voice Preservation? Planned enrollment 60; projected completion date August 2017
 
(NCT01585727) Continuous Intraoperative Monitoring of the Pelvic Autonomic Nerves During Total Mesorectal Excision (TME) for the Prevention of Urogenital and Anorectal Dysfunction in Patients With Rectal Cancer (NEUROS); planned enrollment 188; projected completion date December 2017
 
(NCT01630785) Observation of Neurosurgical Interventions with Intraoperative Neurophysiological Monitoring IONM; planned enrollment 5,000; projected completion date December 2023
 
2018 Update
A literature search was conducted through August 2018.  There was no new information identified that would prompt a change in the coverage statement.  The key identified literature is summarized below.
 
RLN MONITORING DURING THYROID OR PARATHYROID SURGERY
Henry et al reported on a systematic review of meta-analyses published up to February 2017 that compared intraoperative neurophysiologic monitoring (IONM) with direct RLN visualization by assessing rates of vocal fold palsy (Henry, 2017). Reviewers included 8 meta-analyses of RCTs or observational studies (prospective or retrospective) and selected the best evidence, based on the Jadad algorithm. The 8 meta analyses differed significantly in the literature search methodology, databases included, the inclusion of quality assessment, and most did not include a study quality assessment. Using the Jadad algorithm, reviewers determined the meta-analysis by Pisanu et al to have the highest quality; it found that concluded no statistically significant reductions in RLN injury between procedures using IONM vs direct RLN visualization (Pisanu, 2014). However, reviewers also noted that recent developments in IONM technology such as continuous vagal IONM and staged thyroidectomy might provide additional benefits, which were out of the scope of their systematic review and need to be assessed in further assessment in prospective multicenter trials.
 
Sun et al reported on a meta-analysis of RLN injury during thyroid surgery with or without IONM (Sun, 2017). Included were 2 prospective cohort studies and 7 retrospective cohort studies. The absolute risk reduction was 2.75%, with a number needed to treat of 364.13. Observed differences in the subgroup analysis were very imprecise because the number of observed paralyses was very low. IONM was associated with a reduction in overall and permanent RLN palsy in thyroid reoperations. Limitations included small sample sizes and study heterogeneity.
 
RLN MONITORING DURING CERVICAL SPINE SURGERY
Ajiboye et al reported on the results of a systematic review that included 10 studies (total N= 26,357 patients) (Ajiboye, 2017). All studies were of low methodologic quality but had a low risk of bias. Only studies compared the risk of nerve injury using IONM with no IONM. Based on data from these 2 studies, there was no statistically significant difference in the risk of neurologic injury with or without IONM (odds ratio, 0.726; 95% confidence interval [CI], 0.287 to 1.833; p=0.498).

CPT/HCPCS:
92585Auditory evoked potentials for evoked response audiometry and/or testing of the central nervous system; comprehensive
95822Electroencephalogram (EEG); recording in coma or sleep only
95829Electrocorticogram at surgery (separate procedure)
95860Needle electromyography; 1 extremity with or without related paraspinal areas
95861Needle electromyography; 2 extremities with or without related paraspinal areas
95867Needle electromyography; cranial nerve supplied muscle(s), unilateral
95868Needle electromyography; cranial nerve supplied muscles, bilateral
95870Needle electromyography; limited study of muscles in 1 extremity or non-limb (axial) muscles (unilateral or bilateral), other than thoracic paraspinal, cranial nerve supplied muscles, or sphincters
95907Nerve conduction studies; 1-2 studies
95908Nerve conduction studies; 3-4 studies
95909Nerve conduction studies; 5-6 studies
95910Nerve conduction studies; 7-8 studies
95911Nerve conduction studies; 9-10 studies
95912Nerve conduction studies; 11-12 studies
95913Nerve conduction studies; 13 or more studies
95925Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in upper limbs
95926Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in lower limbs
95927Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in the trunk or head
95928Central motor evoked potential study (transcranial motor stimulation); upper limbs
95929Central motor evoked potential study (transcranial motor stimulation); lower limbs
95930Visual evoked potential (VEP) checkerboard or flash testing, central nervous system except glaucoma, with interpretation and report
95933Orbicularis oculi (blink) reflex, by electrodiagnostic testing
95937Neuromuscular junction testing (repetitive stimulation, paired stimuli), each nerve, any 1 method
95938Short-latency somatosensory evoked potential study, stimulation of any/all peripheral nerves or skin sites, recording from the central nervous system; in upper and lower limbs
95939Central motor evoked potential study (transcranial motor stimulation); in upper and lower limbs
95940Continuous intraoperative neurophysiology monitoring in the operating room, one on one monitoring requiring personal attendance, each 15 minutes (List separately in addition to code for primary procedure)
95941Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby) or for monitoring of more than one case while in the operating room, per hour (List separately in addition to code for primary procedure)
95955Electroencephalogram (EEG) during nonintracranial surgery (eg, carotid surgery)
G0453Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby), per patient, (attention directed exclusively to one patient) each 15 minutes (list in addition to primary procedure)

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