Nerve Conduction Studies

Number: 0502

Table Of Contents

Policy

Scope of Policy

This Clinical Policy Bulletin addresses nerve conduction studies.

1. Medical Necessity

   Aetna considers nerve conduction velocity (NCV) studies medically necessary when the following criteria are met:

   1. Member has any of the following indications:

      1. Diagnosis and prognosis of traumatic nerve lesions (e.g., spinal cord injury, trauma to nerves); or
      2. Diagnosis and monitoring of neuromuscular junction disorders (e.g., myasthenia gravis, myasthenic syndrome) using repetitive nerve stimulation; or
      3. Diagnosis of muscle disorders (e.g., myositis, myopathy); or
      4. Diagnosis or confirmation of suspected generalized neuropathies (including uremic, metabolic or immune) (e.g., amyotrophic lateral sclerosis, Guillain-Barré Syndrome, muscular dystrophy, post-polio syndrome); or
      5. Differential diagnosis of physical examination findings of sensory loss, weakness and/or muscle atrophy with no known etiology (e.g., diabetes, hypothyroidism, lupus, rheumatoid arthritis, etc.); or
      6. Differential diagnosis of symptom-based complaints (e.g., pain in limb or joint, weakness, fatigue, cramps, twitching (fasciculations), disturbance in skin sensation or paresthesias [numbness or tingling]) provided the clinical assessment supports the need for a study; or
      7. Localization of focal neuropathies or compressive lesions (e.g., Bell's palsy of the facial nerve, carpal tunnel syndrome [see selection criteria below], cubital tunnel syndrome [see selection criteria below], tarsal tunnel syndrome, nerve root compression, neuritis, motor neuropathy, mononeuropathy, radiculopathy [see selection criteria below], plexopathy); or
      8. Peripheral neuropathy - unexplained peripheral neuropathy with pain of a neuropathic pattern, and with demonstrated motor loss or sensory loss, all of unknown etiology; and
   2. The member has had a needle electromyographic (EMG) study to evaluate the condition either concurrently or within the past year. The requirement for needle EMG with NCV may be waived for persons on anti-coagulant therapy with warfarin (Coumadin), direct thrombin inhibitors (e.g., dabigatran (Pradaxa), desirudin (Iprivask)), or heparins that can not be interrupted. It may also be waived when the purpose of the NCV study is solely to diagnose or rule out one of the following: carpal tunnel syndrome, Charcot-Marie-Tooth disease,myasthenia gravis or Lambert-Eaton myasthenic syndrome; and
   3. The following disease-specific criteria are met, where applicable:

      1. Carpal tunnel syndrome

         For evaluation of individuals suspected of having carpal tunnel syndrome:

         1. Sensory conduction studies across the wrist of the median nerve, and if the results are abnormal, of one other sensory nerve in the symptomatic limb; and
         2. If the initial median sensory nerve conduction study across the wrist has a conduction distance greater than 8 cm, and the results are normal, additional studies as listed below:
            
            
            1. Comparison of median sensory conduction across the wrist with radial or ulnar sensory conduction across the wrist in the same limb; or
            2. Median sensory conduction across the wrist over a short (7 to 8 cm) conduction distance;

         3. Motor conduction studies of the median nerve recording from the thenar muscle and of one other nerve in the symptomatic limb to include measurement of distal latency;

      2. Cervical, thoracic or lumbar radiculopathy

         For evaluation of cervical, thoracic or lumbar radiculopathy when all of the following criteria are met:

         1. Persistent or progressive symptoms; and
         2. Failed conservative treatment (eg, medications, physical therapy, etc. for at least a four week period); and
         3. Unexplained by imaging studies (eg, magnetic resonance imaging [MRI], myelogram, etc.)

      3. Diabetic peripheral neuropathy

         For persons with diabetes who have persistent or progressive symptoms of neuropathy despite conservative treatments (e.g., medications, well-fitting shoes).

         Aetna considers NCVs experimental, investigational, or unproven for screening for diabetic neuropathy and for monitoring disease intensity and response to treatment.

      4. Cubital tunnel syndrome criteria

         For individuals with symptoms and positive physical signs of distribution region of ulnar nerve (e.g., pains and numbness of the forearm and finger, weakness of hands and muscles atrophy).

         Aetna considers NCV studies experimental, investigational, or unproven when these criteria are not met.

   4. Frequency of Testing

      The following table lists the American Association of Neuromuscular & Electrodiagnostic Medicine's (formerly known as American Association of Electrodiagnostic Medicine) recommendations concerning a reasonable maximum number of NCV, needle EMG and other EMG studies per diagnostic category needed for a physician to render a diagnosis:

      Note: This table provides the medically necessary maximal number of nerve conduction studies; it does NOT imply that an F-wave study is necessary for carpal tunnel syndrome.

      Table: Reasonable Maximum Number of Nerve Conduction Studies, Needle EMG, and other EMG Studies

      	Needle EMG	Nerve Conduction Studies		Other EMG Studies
      Indications	Needle EMG Count	Motor NCV studies with and/or without Fwave	Sensory NCV studies	H-Reflex	Neuromuscular Junction Testing (Repetitive Stimulation)
      Carpal tunnel (unilateral)	1	3	4	--	--
      Carpal tunnel (bilateral)	2	4	6	--	--
      Radiculopathy	2	3	2	2	--
      Mononeuropathy	1	3	3	2	--
      Polyneuropathy/Mononeuropathy Multiplex	3	4	4	2	--
      Myopathy	2	2	2	--	2
      Motor Neuropathy	4	4	2	--	2
      Plexopathy	2	4	6	2	--
      Neuromuscular junction	2	2	2	--	3
      Tarsal tunnel syndrome (unilateral)	1	4	4	--	--
      Tarsal tunnel syndrome (bilateral)	2	5	6	--	--
      Weakness, fatigue, cramps, or twitching (focal)	2	3	4	--	2
      Weakness, fatigue, cramps, or twitching (general)	4	4	4	--	2
      Pain, numbness, or tingling (unilateral)	1	3	4	2	--
      Pain, numbness, or tingling (bilateral)	2	4	6	2	--

      Source: AMA, 2015.

      Utilization of motor or sensory nerve conduction velocity studies at a frequency of 2 sessions per year would be considered appropriate for most conditions (e.g., unilateral or bilateral carpal tunnel syndrome, radiculopathy, mononeuropathy, polyneuropathy, myopathy, and neuromuscular junction disorders).  Nerve conduction velocity studies performed more frequently than twice a year may be reviewed for medical necessity. 

      1. F-waves and H-reflex studies are performed to evaluate nerve conduction in portions of the nerve more proximal (near the spine) and, therefore, inaccessible to direct assessment using conventional techniques. Electrical stimulation is applied on the skin surface near a nerve site in a manner that sends impulses both proximally and distally. Characteristics of the response are assessed, including latency. Late responses provide information in the evaluation of radiculopathies, plexopathies, polyneuropathies (especially with multifocal conduction block or in suspected Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy), and proximal mononeuropathies. In some cases, they may be the only abnormal study.
      2. Motor and sensory NCV studies and late responses (F-waves and H-reflex studies) are often complementary and performed during the same evaluation.

   5. H-Reflex Studies

      1. Typically, only 2 H-reflex studies are performed in a given examination.
      2. H-reflex studies usually must be performed bilaterally because symmetry of responses is an important criterion for abnormality. When a bilateral H-reflex study is performed, the entire procedure must be repeated, increasing examiner time and effort; there are no economies of scale in multiple H-reflex testing.
      3. H-reflex studies usually involve assessment of the gastrocnemius/soleus muscle complex in the calf. Bilateral gastrocnemius/soleus H-reflex abnormalities are often early indications of spinal stenosis, or bilateral S1 radiculopathies.
      4. In rare instances, H-reflexes need to be tested in muscles other than the gastrocnemius/soleus muscle, e.g., in the upper limbs. In conditions such as cervical radiculopathies or brachial plexopathies, an H-reflex study can be performed in the arm (flexor carpi radialis muscle). Other muscles that may be tested, although rarely, are the intrinsic small muscles of the hand and foot.

   6. F-Wave Studies

      1. Although the set-up for an F-wave study is similar to the set-up for a motor NCV study, the testing is carried out separately from motor NCV study, utilizing different machine settings and separate stimulation to obtain a larger number of responses (at least 10).
      2. The number of F-wave studies, which need to be performed on a given person, depends on the working diagnosis and the electrodiagnostic findings already in evidence. It may be appropriate in the same person to perform some motor NCV studies with an F-wave and others without an F-wave.

   7. Blink Reflexes

      To evaluate disease involving the 5th or 7th cranial nerves or brainstem. Blink reflexes are considered experimental, investigational, or unproven for all other indications. The blink reflex is an electrodiagnostic analog of the corneal reflex. The latency of the responses, including side-to-side differences, can help localize pathology in the region of the 5th or 7th cranial nerves, or in the brainstem. The latencies and amplitudes of directly elicited facial motor responses should be determined to exclude a peripheral abnormality if the blink reflexes are abnormal.

      Recordings should be made bilaterally with both ipsilateral and contralateral stimulation.

   8. Neuromuscular Junction Testing

      To diagnose persons with fatigable weakness who are being evaluated for possible disease of the neuromuscular junction:

      1. Myasthenia gravis; or
      2. Congenital myasthenic syndrome; or
      3. Lambert-Eaton myasthenic syndrome; or
      4. Botulinism; or
      5. Autoimmune neuromyotonia; or
      6. Myopathy; or
      7. Motor neuropathy (e.g., amyotrophic lateral sclerosis); or
      8. Symptoms of diplopia, dysphagia, or fatigable weakness that increases with repetitive activity.

2. Experimental, Investigational, or Unproven

   Aetna considers the following interventions experimental, investigational, or unproven because the effectiveness of these approaches has not been established:

   1. Electro-diagnostic tests (e.g., EMG and NCV studies) for the diagnosis of distal symmetric polyneuropathy;
   2. Examination/NCV studies using the ADVANCE NCS/EMG System, Brevio NCS monitor, Cadwell Sierra, NC-stat DPNCheck, NC-stat monitor, Neural Scan - Axon II, VT3000, XLTEK Neuropath, and other automated devices;
   3. F-wave (F-reflex) study for carpal tunnel syndrome;
   4. Intraoperative NCV studies during prostatectomy/prostate surgery;
   5. Intraoperative NCV studies for wrist arthroscopy repair;
   6. NCV studies for the diagnosis of organophosphorus pesticide exposure;
   7. NCV studies for intraoperative neuromonitoring;
   8. NCV studies for screening for polyneuropathy of diabetes or end-stage renal disease;
   9. NCV studies for the sole purpose of monitoring disease intensity or treatment effectiveness for polyneuropathy of diabetes or end-stage renal disease;
   10. Phrenic nerve conduction study for evaluation of phrenic nerve function of lung transplant candidate;
   11. The Medi-Dx 7000™ and Neural-Scan. 

   Note: Surface electrodes are usually employed for both stimulation and recording. Needle electrodes may be used when there is a need to evaluate a nerve that is deep in the tissue, such as the sciatic nerve in the thigh, or the femoral nerve in an extremely obese individual. 

3. Related Policies

   • CPB 0112 - Surface Scanning and Macro Electromyography
   • CPB 0357 - Quantitative Sensory Testing Methods

Background

Nerve conduction testing, also known as nerve conduction studies (NCS) and nerve conduction velocity (NCV) testing, measures the speed of conduction of impulses through a nerve. The impulses that are measured are generated by placing a stimulating electrode on the skin over the nerve. Recording electrodes are placed at various distances from the stimulating electrode. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals. There are two parts to NCS: testing motor nerves and testing sensory nerves. NCS are performed by a physician specially trained in electrodiagnostics.

Nerve conduction velocity studies are performed by recording and studying the electrical responses from peripheral nerves or the muscle they innervate, following electrical stimulation of the nerve.  Usually surface electrodes are employed for both stimulation and recording because of their reproducibility and ease of use.  Needle electrodes may be used when there is a need to evaluate a nerve that is deep in the tissue, such as the sciatic nerve in the thigh, or the femoral nerve in an extremely obese individual.

Motor NCS are performed by stimulating two different points along a nerve and the impulse is measured by an electrode that is placed over the muscle being stimulated by that nerve. This measure is called the latency and is measured in milliseconds. The size of the response, called the amplitude, is measured in millivolts.

Sensory NCS are measured with a single stimulating electrode and a single recording electrode. This test is calculated based upon the latency and the distance between the stimulating and recording electrode.

Additional types of NCS, referred to as late responses, are H-reflex and F-wave tests. These tests are usually performed on nerves that are more proximal (near) to the spine and, therefore, inaccessible to direct assessment using conventional techniques. These tests can be helpful when evaluating radiculopathies, plexopathies, polyneuropathies and proximal mononeuropathies.

• H-reflex study uses stimulation of a nerve and records the reflexive electrical discharge from a muscle in the limb. It also measures the conduction between the limb and spinal cord. The impulses going toward the spinal cord are known as afferent impulses and those moving away from the spinal cord are efferent impulses.
• F-wave study includes an electrical stimulation that is applied to the skin surface proximal to the distal portion of a nerve so that the impulse travels both toward the muscle fiber and back to the motor neurons of the spinal cord.

In standard NCV testing, the stimulating, recording and ground electrode placement and the test design should be individualized to each patient's specific anatomy.  Nerves tested should be limited to the specific nerves and conduction studies needed for the particular clinical question being investigated.  The stimulating electrode is placed directly over the nerve to be tested, and stimulation parameters are adjusted to avoid stimulating other nerves or nerve branches.  In most motor nerve conduction studies, and in some sensory and mixed nerve conduction studies, both proximal and distal stimulation are used.  Motor nerve conduction study recordings are made from electrodes placed directly over the motor point of the specific muscle to be tested.  Sensory nerve conduction study recordings are made from electrodes placed directly over the specific nerve to be tested.  Waveforms should be reviewed on site in real time, and the technique (stimulus site, recording site, ground site, filter settings) should be adjusted as the test proceeds in order to minimize artifact, and to minimize the chances of unintended stimulation of adjacent nerves and the unintended recording from adjacent muscles or nerves.  Reports are prepared on site by the examiner, and consist of the interpretation of test results, using established techniques to assess the amplitude, latency and configuration of waveforms elicited by stimulation at each site of each nerve tested.  This includes the calculation of NCV, sometimes including specialized F-wave indices, along with comparison to normal values, summarization of clinical and electrodiagnostic data, physician interpretation, generation of a differential diagnosis, and, when appropriate, suggestions for additional testing.  Electromyoraphic recording is usually performed during the same patient encounter in order to carry out a more in-depth evaluation of the clinical question being investigated.

Standard NCV testing includes safeguards and procedures to assure proper performance and interpretation.  Many of those are not used in the automated nerve testing systems.  Therefore, literature about NCV testing of clinical efficacy does not necessarily apply to these automated devices.

Automated devices, also known as point of care devices, perform limited nerve conduction tests and do not supplement, replace or duplicate traditional nerve conduction tests. Examples of these devices include, but may not be limited to, the ADVANCE NCS/EMG system, Brevio NCS monitor, NC–stat system and the Neural Scan - Axon II. Automated NCV testing is similar to standard NCV testing in that both involve electrical stimulation of peripheral nerves, and recording of electrical responses from the same peripheral nerve or from a muscle.  Automated devices, however, have a number of differences with standard NCV tests.

With standard NCV studies, the physician specialist and a registered technologist perform the testing.  With automated devices, the office staff typically perform the test.  With automated devices, only several specific nerves can be tested.  Whereas standard NCV tests can stimulate and record both proximally and distally, automated devices can only stimulate and record distally.  With automated devices, only one direction of conduction is available, whereas with standard NCV tests, orthodromic and antidromic conduction is available.  The technique of standard NCV tests varies according to the patient's situation, whereas with automated devices, a single specific technique is pre-determined.  With automated devices, electromyography (EMG) is generally not available at the point of service, although new automated devices are being developed that also have EMG capabilities.  Stimulator and recording sites are placed at pre-determined anatomic locations with automated devices, whereas with standard NCV testing, stimulator and recording sites can be moved around to find optimal locations.

With standard NCV tests, a trained clinician evaluates patient’s history and examination findings, determines what electrodiagnostic testing is needed to answer the clinical question at hand.  The clinician can consider the differential diagnosis as testing is conducted, and change the test as needed as it proceeds to narrow the differential diagnosis.  The clinician asks further history and checks further examination findings, and integrates those with test findings in developing an interpretation.  By contrast, automated NCV devices test preset nerves only.

With standard NCV testing, a trained clinician scores peaks, latencies, determines if tests are normal, adjusted to clinically relevant factors.  The clinician assesses latencies, amplitudes, configurations, and conduction velocities.  The clinician critiques tracings, and determines if repeat recordings needed.  The clinician takes into account the patient’s history, physical, NCV and EMG as needed when interpreting the results.  The clinician also considers normal variants.  By contrast, with automated devices, a computer scores amplitudes and latencies, and determines if tests are normal according to a look-up table.  The computer prints an automated interpretation statement for the physician to sign; the computer’s statement is taken from a programmed list of statements.

The NC-Stat Monitor (NeuroMetrix Inc., Waltham, MA) is an automated hand-held device using proprietary technology for conducting NCS.  According to the manufacturer, the NC-stat System is equivalent to larger, more expensive NCS/EMG instruments.  The monitor is intended to measure standard nerve conduction parameters such as amplitude, latency, and conduction velocity of the motor as well as sensory nerves.  The NC-stat System has been on the market since 1999; and recently received an updated Food and Drug Administration (FDA) 510(k) clearance.  The NC-Stat was initially cleared for marketing by the FDA as a device to measure neuromuscular signals as an adjunct to, and not a replacement for, conventional electrodiagnostic measurements.  The updated intended use language is "[t]he NeuroMetrix NC-stat is intended to stimulate and measure neuromuscular signals that are useful in diagnosing and evaluating systemic and entrapment neuropathies".  However, the Code of Federal Regulations clarifies that clearance for marketing under Section 510(k) does not in any way denote official approval of the device.  Clearance for marketing does not involve approval for the specific usefulness, or evidence of net health outcomes, in any specific patient population or disease categories.  These health care considerations generally depend on published literature.  The NC-stat System is designed to perform non-invasive NCS for patients with suspected upper and lower extremity disorders/diseases (e.g., carpal tunnel syndrome, low back pain/sciatica, and diabetic peripheral neuropathy).  

The available evidence for the NC-stat monitor is limited in comparison with standard NCV studies and needle EMG.  In the largest study of the NC-stat technology published to date, Katz (2006) established a normal data set for median nerve studies in industrial workers using NC-stat technology.  A total of 1,695 individuals applying for employment at a single heavy industry plant without symptoms of carpal tunnel syndrome (CTS) were studied.  Values for median distal motor latency (DML), amplitude, and F-waves were recorded in the dominant limbs.  The DML was 3.81 +/- 0.57 milliseconds, with a 95 % cut-off value of 4.75 milliseconds.  Amplitude of the compound muscle action potential was 0.95 +/- 0.46 mV, reflecting the use of volume conduction by this technology.  Most of the workers who were characterized as having borderline, prolonged, or very prolonged distal motor latencies according to NeuroMetrix automated report actually fell below the 95 % cut-off of this independent data analysis.  The author concluded that the NC-stat technology using DML appears to be no more sensitive or specific than a traditionally performed DML for the diagnosis of CTS.  Until recently promoted sensory studies using NC-stat technology are better defined, this technology can not be recommended for screening or diagnosis of CTS in an industrial population.

A technology assessment of this device, prepared by the Washington State Department of Labor and Industries (Morse, 2006): "The evidence evaluating the use of NC-stat is most abundant for nerve testing that may be useful to diagnose or screen for conditions at the wrist (i.e., Median and ulnar nerve studies).  There is very little or no available evidence (high quality, peer-reviewed) supporting the use of NC-stat and specific biosensors for testing of nerves in the lower extremities .... At this time there is not adequate scientific evidence to conclude that NC-stat is equivalent to traditional nerve conduction study methods for use in evaluating the functioning of the median, ulnar, peroneal, sural or tibial nerves.  The diagnostic accuracy of NC-stat is not yet demonstrated in the scientific literature to be equivalent to traditional or gold-standard testing methods.  NC-stat is therefore considered experimental and investigational .... NC-stat is considered controversial as the performance of testing at the point-of-service may not be supported by recommendations of the American Association of Neuromuscular & Electrodiagnostic Medicine."

Work-Loss Data Institute evidence-based guidelines on CTS (2006) stated that NC-stat monitoring is "not currently recommended."

The Brevio NCS-Monitor (NeuMed Inc., West Trenton, NJ) is a hand-held automated device designed to assess peripheral nerves for conditions such as CTS, diabetic peripheral neuropathy, and tarsal tunnel syndrome.  The latest version of the Brevio has a graphical user interface that integrates on-screen prompts to guide a user during an examination.  The device utilizes sophisticated firmware with algorithms that seek a maximal compound muscle action potential (CMAP) or sensory nerve action potential (SNAP), plots waveform images in real-time, marks all cursors, and indicates whether or not the latency and amplitude are within normal limits.  Upon completion of a full examination, the device can generate a report.  The whole examination process (including printing of the report) will take about 15 mins.  There is insufficient evidence to establish the clinical value of this automated NCV studies device.

Schmidt et al (2011) noted that automated hand-held NCS devices are being marketed for use in the diagnosis of lumbosacral radiculopathy (LSR).  In this study, these researchers compared the specificity and sensitivity of a hand-held NCS device for the detection of LSR with standard electrodiagnostic study (EDX).  A total of 50 patients referred to a tertiary referral EMG laboratory for testing of predominantly unilateral leg symptoms (weakness, sensory complaints, and/or pain) were included in the investigation; 25 normal "control" subjects were later recruited to calculate the specificity of the automated protocol.  All patients underwent standard EDX and automated testing.  Raw NCS data were comparable for both techniques; however, computer-generated interpretations delivered by the automated device showed high sensitivity with low specificity (i.e., many false-positives) in both symptomatic patients and normal controls.  The authors concluded that automated device accurately recorded raw data, but the interpretations provided were overly sensitive and lacked the specificity necessary for a screening or diagnostic examination.

The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) states that nerve conduction studies performed independent of needle EMG may only provide a portion of the information needed to diagnose muscle, nerve root and mostnerve disorders.

When NCS is used on its own without integrating needle EMG findings or when an individual relies solely on a review of NCS data, the results can be misleading and important diagnoses may be missed. Individuals may thus be subjected to incorrect, unnecessary, and potentially harmful treatment interventions. 

The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM, 2005) stated that based on the literature, there are no contraindications to needle EMG in patients with lymphedema or prosthetic joints.  In patients with lymphedema, clinical judgment in each individual circumstance should be used in deciding whether the risk of complication is greater than the value of the information to be obtained from the needle electrode examination.  Thus, chronic lymphedema (from breast cancer surgery) is not a contraindication to the EMG requirement with nerve conduction velocity studies.

The AANEM (2006) states that "the standard of care in clinical practice dictates that using a predetermined or standardized battery of NCSs for all patients is inappropriate".  "It is the position of the AANEM that, except in unique situations, NCSs and needle EMG should be performed together in a study design determined by a trained neuromuscular physician".  The AANEM explained that standardized nerve conduction studies performed independent of needle EMG studies may miss data essential for an accurate diagnosis.  The AANEM position statement (2006) explains that "[t]he performance of or interpretation of NCS separately from the needle EMG component of the testing should clearly be the exception.  Nerve conduction studies performed independent of needle EMG may only provide a portion of the information needed to diagnose muscle, nerve root, and most nerve disorders.  When the NCS is used on its own without integrating needle EMG findings, or when an individual relies solely on a review of NCS data, the results can be misleading and important diagnoses may be missed.  Moreover, individuals who interpret NCV data without patient interaction or who rely on studies that have delayed interpretation, who have interpretation made off-site, and who interpret results without complementary information obtained from EMG studies are not meeting the standards outlined in the AANEM policy recommendations."

Nerve conduction studies are essential in diagnosing carpal tunnel syndrome. EMG is useful optional test for identifying other conditions that may have a similar presentation. However, even for carpal tunnel syndrome, the lack of an EMG study may mean that a diagnosis is missed. The AANEM guidelines explain: "Additionally, patients typically need to have both NCSs and needle EMG to ensure that an underlying medical condition is not missed. For example, in patients with carpal tunnel syndrome (CTS), other disorders can coexist, such as a radiculopathy, brachial plexopathy, or underlying peripheral neuropathy. Alternatively, there may be a problem involving the median nerve but localized at a site more proximal than the wrist. These other problems are far more likely to be misdiagnosed or missed completely if the needle EMG is not performed, and if a physician without the proper skill and training is interpreting the data, making a diagnosis, and establishing a treatment plan. Surgical release of the median nerve at the wrist, a treatment for CTS, would be an inappropriate and unnecessary procedure if the patient does not have CTS. Additionally, NCSs may be normal, but the needle EMG examination may demonstrate abnormalities that identify a more proximal nerve lesion that produces symptoms such as numbness in the hand and that may mimic CTS."

Needle EMG is relatively contraindicated in persons on anti-coagulant therapy with coumadin (Warfarin) or heparins that cannot be interrrupted.  Oh (2003) observed that patients with a variety of bleeding disorders may be referred for needle EMG.  Oh recommended that the referring physician and the electromyographer examine each case individually, carefully weighing the potential risks and benefits.  An increased potential for bleeding may be expected in patients with thrombocytopenia who have a platelet count of less than 50,000/cm3, with a prothrombin time of more than 1.5 to 2 times the control values (International Normalized Ratio of 1.5 to 2.0), or with a partial thromboplastin time greater than 1.5 to 2 times the control value when intravenous heparin therapy is administered (Oh, 2003).  Oh (2003) advised that, if the decision is made to perform a needle EMG in such a patient, the clinician should first to examine the small, superficial muscles and to watch for bleeding problems.  The author noted, however, that additionally prolonged local pressure is usually sufficient for hemostatis.  This is also the case with patients who have other coagulopathies or who are receiving anti-coagulants (Oh, 2003).  Oh (2003) stated that needle examinations should be avoided in patients with hemophilia and other hereditary coagulation disorders unless clotting functions have first been appropriately corrected.  Oh (2003) noted that there has been 1 report of a complication of subcutaneous bleeding secondary to the needle EMG in a patient receiving anti-coagulants and with a partial thromboplastin time greater than twice the control value.

In a discussion of complications from EMG examinations, Kuminga (2001) stated that bleeding tendencies deserve special mention in screening patients for electromyographic examination.  Kuminga (2001) stated that specific inquiry in this regard often reveals pertinent information that the patient may not volunteer.  To prevent unnecessary complications, the author recommends that the electromyographer consult with the referring physician to weight the diagnostic benefits against the risks.  A patient taking anti-coagulants should have appropriate laboratory tests for bleeding tendency prior to a needle study (Kuminga, 2001).  With heparin infusion, partial thromboplastin time should not exceed 1.5 of control value.  With warfarin (Coumadin) therapy, patients should have an international rating (INR) less than 2.0.  Kouminga (2001) stated that the same precautions should apply to those with other coagulopathy, such as hemophiia.  For thrombocytopenia, unless the platelet count falls below 20,000/mm, local pressure can usually counter the minimal hemorrhage.  The author noted that testing the degree of bleeding tendency with a superficial muscle helps determine the feasibility of further study of deeper muscles, which can not be compressed adequately to accomplish hemostasis.

Authorities recommend that patients on warfarin should stop taking warfarin 3 days prior to EMG and resume taking it immediately after the test, if permitted by their primary physician.  The use of aspirin, or aspirin-like medications (such as Plavix (clopidogrel) or Aggrenox (aspirin and dipyridamole)) is not a contraindication to the test.

An assessment of the Brevio by the Washington State Department of Labor and Industries (2007) concluded that "At this time there appears to be no evidence addressing the diagnostic accuracy of the Brevio nerve conduction system.  There is adequate evidence available to evaluate the predicate and predecessor device to the Brevio, the Nervepace.  This evidence does not support the accuracy or reliability of Nervepace for use as a diagnostic or screening tool for any condition(s) and specifically for carpal tunnel syndrome".

The American Association of Neuromuscular and Electrodiagnostic Medicine’s report on "Risks in Electrodiagnostic Medicine" (2009) stated that "Needle EMG recording does not introduce electrical current into the body and, therefore, poses no risk of interference with implanted cardiac devices". 

Karami-Mohajeri et al (2014) presented a systematic review of the recent literature on the scientific support of EMG and NCV in diagnosing the exposure and toxicity of organophosphorus pesticides (OP).  Specifically, this review focused on changes in EMG, NCV, occurrence of intermediate syndrome (IMS), and OP-induced delayed polyneuropathy (OPIDN) in human.  All relevant bibliographic databases were searched for human studies using the key words "OP poisoning", "electromyography", "nerve conduction study," and "muscles disorders".  Intermediate syndrome usually occurs after an acute cholinergic crisis, while OPIDN occurs after both acute and chronic exposures.  Collection of these studies supported that IMS is a neuromuscular junction disorder and can be recorded upon the onset of respiratory failure.  Due to heterogeneity of reports on outcomes of interest such as motor NCV and EMG amplitude in acute cases and inability to achieve precise estimation of effect in chronic cases meta-analysis was not helpful to this review.  The OPIDN after both acute and low-level prolonged exposures develops peripheral neuropathy without preceding cholinergic toxicity and the progress of changes in EMG and NCV is parallel with the development of IMS and OPIDN.  Persistent inhibition of acetylcholinesterase (AChE) is responsible for muscle weakness, but this is not the only factor involved in the incidence of this weakness in IMS or OPIDN suggestive of AChE assay not useful as an index of nerve and muscle impairment.  The authors concluded that although several mechanisms for induction of this neurodegenerative disorder have been proposed, among them oxidative stress and resulting apoptosis can be emphasized.  Nevertheless, they stated that there is little synchronized evidence on subclinical electrophysiological findings that limit these investigators to reach a strong conclusion on the diagnostic or prognostic use of EMG and NCV for acute and occupational exposures to OPs.

Furthermore, an UpToDate review on "Organophosphate and carbamate poisoning" (Bird, 2014) states that "The diagnosis of organophosphate or carbamate poisoning is made on clinical grounds …. Laboratory abnormalities – Direct measurement of RBC acetylcholinesterase (RBC AChE) activity provides a measure of the degree of toxicity.  Sequential measurement of RBC AChE activity (if rapidly available) may also be used to determine the effectiveness of oxime therapy in regeneration of the enzyme.  Determination of RBC AChE activity can also be helpful in evaluating chronic or occupational exposure.  However, most hospital laboratories are unable to perform this test.  An assay for plasma (or pseudo-) cholinesterase activity is more easily performed, but does not correlate well with severity of poisoning and should not be used to guide therapy".  The review does not mention the use of NCV studies as a diagnostic tool.

Distal Symmetric Polyneuropathy

Callaghan et al (2015) noted that peripheral neuropathy is a highly prevalent and morbid condition affecting 2 % to 7 % of the population. Patients frequently experience pain and are at risk of falls, ulcerations, and amputations.  These investigators reviewed recent diagnostic and therapeutic advances in DSP.  Current evidence supports limited routine laboratory testing in patients with DSP.  Patients without a known cause should undergo a complete blood cell count, comprehensive metabolic panel, vitamin B12 measurement, serum protein electrophoresis with immune-fixation, fasting glucose measurement, and glucose tolerance test.  The presence of atypical features such as asymmetry, non-length dependence, motor predominance, acute or sub-acute onset, and prominent autonomic involvement should prompt a consultation with a neurologist or neuromuscular specialist.  Electro-diagnostic tests and magnetic resonance imaging (MRI) of the neuro-axis contribute substantial cost to the diagnostic evaluation, but evidence supporting their use is lacking.  Strong evidence supports the use of tricyclic anti-depressants, serotonin norepinephrine reuptake inhibitors, and voltage-gated calcium channel ligands in the treatment of neuropathic pain.  More intensive glucose control substantially reduces the incidence of DSP in patients with type 1 diabetes but not in those with type 2 diabetes.  The authors concluded that the opportunity exists to improve guideline-concordant testing in patients with DSP.  Moreover, they stated that the role of electro-diagnostic tests needs to be further defined, and interventions to reduce MRI use in this population are needed.  Furthermore, they noted that even though several effective medications exist for neuropathic pain treatment, pain is still under-recognized and under-treated; new disease-modifying medications are needed to prevent and treat peripheral neuropathy, especially in type 2 diabetes.

Diabetic Sensorimotor Polyneuropathy

Schamarek and colleagues (2016) noted that subclinical inflammation has been implicated in the development of diabetic sensorimotor polyneuropathy (DSPN), but studies using electrophysiological assessment as outcomes are scarce.  These investigators examined associations of biomarkers reflecting different aspects of subclinical inflammation with motor and sensory NCV in individuals with diabetes.  Motor and sensory NCV was assessed in individuals with recently diagnosed type 2 (n = 352) or type 1 diabetes (n = 161) from the baseline cohort of the observational German Diabetes Study; NCV sum scores were calculated for median, ulnar and peroneal motor as well as median, ulnar and sural sensory nerves.  Associations between inflammation-related biomarkers, DSPN and NCV sum scores were estimated using multiple regression models.  In type 2 diabetes, high serum interleukin (IL)-6 was associated with the presence of DSPN and reduced motor NCV.  Moreover, higher levels of high-molecular weight (HMW) adiponectin, total adiponectin and their ratio were associated with prevalent DSPN and both diminished motor and sensory NCV, whereas no consistent associations were observed for C-reactive protein (CRP), IL-18, soluble intercellular adhesion molecule-1 and E-selectin.  In type 1 diabetes, only HMW and total adiponectin showed positive associations with motor NCV.  The authors concluded that these findings pointed to a link between IL-6 and both DSPN and slowed motor NCV in recently diagnosed type 2 diabetes.  They stated that the reverse associations between adiponectin and NCV in type 1 and type 2 diabetes are intriguing, and further studies should explore whether they may reflect differences in the pathogenesis of DSPN in both diabetes types.

NC-stat DPNCheck

Chatzikosma and colleagues (2016) evaluated the utility of automated NCS of the sural nerve with a new portable device for the diagnosis of diabetic polyneuropathy (DPN) in patients with type 2 diabetes mellitus (T2DM).  This study included 114 T2DM patients (58 men) with mean age 64.60 ± 8.61 years.  Exclusion criteria were B12 depletion, alcohol abuse and other causes of PN.  The reference method was the Neuropathy Disability Score (NDS) with a threshold NDS greater than or equal to 3.  Sural nerve automated NCS was performed with the portable NC-stat DPNCheck device.  Sensory nerve conduction velocity and sensory nerve action potential amplitude were measured bilaterally.  Automated NCS was considered abnormal when greater than or equal to 1 of the 2 afore-mentioned neurophysiological parameters was abnormal in at least 1 leg.  Examination with NC-stat DPNCheck exhibited 90.48 % sensitivity, 86.11 % specificity, 79.17 % positive predictive value (PPV) and 93.94 % negative predictive value (NPV).  The positive likelihood ratio (LR+) was 6.51 and the negative likelihood ratio (LR-) was 0.11.  Sural nerve automated NCS with the NC-stat DPNCheck device exhibits high sensitivity and specificity for the diagnosis of DPN in T2DM.  The authors concluded that  the findings of this study suggested that sural nerve automated NCS with the NC-stat DPNCheck device exhibited high sensitivity and specificity for the diagnosis of clinical DPN in T2DM.  This high diagnostic performance suggested that the test may prove useful as a screening tool of DPN, with a particular utility in exclusion of this condition.  The present results added to the increasing appreciation of the importance that automated NCS may have in improving diagnosis of DPN, including the primary health care setting.

The authors stated that this study had several drawbacks.  First, they included patients from a tertiary care setting, and therefore the results may not be directly applicable to the general diabetic population.  Second, they did not confirm the diagnosis of DPN by classical NCS.  Lastly, they only studied patients with T2DM, and so more experience with T1DM is needed.

Vogt and colleagues (2017) stated that scant information is available about the prevalence of DPN, as well as the applicability of screening tools in sub-Saharan Africa..  These investigators examined these issues in Zanzibar (Tanzania).  A total of 100 consecutive diabetes patients were included in this study.  These researchers also investigated self-reported numbness of the lower limbs, 10-point monofilament test, the Sibbald 60-s Tool, and NCS using an automated handheld point-of-care device, the NC-stat DPNCheck.  Mean age was 54 years, 90 % had T2DM, and with 9 year average disease duration.  Mean hemoglobin A1c (HbA1c) was 8.5 %, blood pressure 155/88 mmHg; 62 % reported numbness, 61 % had positive monofilament, and 79 % positive Sibbald tool; NCS defined neuropathy in 45 % of the patients.  Only the monofilament showed appreciable concordance with the NCS, Cohen's κ 0.43.  The authors concluded that these findings suggested the utility of monofilament as a screening tool for DPN and the NC-stat DPNCheck in cases of diagnostic uncertainty or for research purposes in a low resource setting.  Moreover, they stated that in order to address the associated risk of ulcers and amputations, a prospective study in this diabetes population would be of great value.

Hamasaki and Hamasaki (2017) stated that currently, no international diagnostic criteria for diabetic neuropathy (DN) have been established.  Recently, a novel point-of-care (POC) sural nerve conduction device (DPNCheck) has been developed.  These investigators examined associations between DN and clinical parameters related to the development and progression of DN by using this novel device.  These researchers conducted a retrospective observational study in patients with diabetes whose sural nerve functions were measured using DPNCheck between January 2015 and October 2016.  Multiple and logistic regression analyses were conducted to evaluate the associations of sural nerve conduction velocity (SNCV) and amplitude (SNAP) with clinical parameters related to DN.  A total of 740 patients were enrolled in this study.  At baseline, 211 patients were diagnosed with DN by using DPNCheck.  The sensitivity, specificity, and LR+ of DPNCheck compared with ankle reflex as reference were 81 %, 46 %, and 1.5, respectively.  Of these, 182 patients were followed-up for approximately 1 year to measure changes in SNCV and SNAP.  Both SNCV and SNAP were inversely associated with duration of diabetes, plasma glucose levels, and HbA1c levels at baseline, whereas these were positively associated with ankle-brachial index (ABI).  Logistic regression analysis revealed that poor glycemic control was associated with increased risk of reduction in both SNCV [odds ratio [OR] = 1.570; 95 % CI: 1.298 to 1.898; p < 0.001] and SNAP (OR = 1.408; 95 % CI: 1.143 to 1.735; p = 0.001), and longer duration of diabetes was also significantly associated with an increased risk of reduction in both SNCV (OR = 1.058; 95 % CI: 1.032 to 1.084; p < 0.001) and SNAP (OR = 1.049; 95 % CI: 1.019 to 1.079; p = 0.001).  The authors concluded that the findings of this study suggested that early initiation of treatment for diabetes is essential for preventing the progression of DN.  The factors associated with DN were duration of diabetes, glycemic control, and ABI.  Moreover, they stated that this study also showed the utility of DPNCheck in clinical practice, which may be useful as a screening tool to identify DN.

The authors stated that this study had several drawbacks.  First, there were some missing values because of the study design.  Second, these researchers did not measure SNCV and SNAP bilaterally.  The mean duration of diabetes of patients with DN was 17.4 ± 10.1 years in the present study; thus, most patients were expected to have similar bilateral sural nerve impairment.  Third, these investigators did not evaluate patients’ symptoms and certain diagnostic indicators other than ankle reflex such as vibration perception threshold.  They could not evaluate the diagnostic accuracy of DPNCheck because clinical findings; symptoms, signs, and standard nerve conduction study were insufficient.  However, as shown in previous studies, DPNCheck had a high sensitivity and a relatively low specificity in this study.  This device can rule out the presence of DN if the test is negative; however, it is not suitable for the definitive diagnosis of DN.  Fourth, there should have been a heterogeneity of physical examination between diabetologists in this study.  Fifth, post-hoc sample size calculation was also a limitation.  Finally, according to the National Health and Nutrition Survey in 2008, the prevalence of DN in Japanese patients with diabetes was 11.8 %; thus, the authors could not generalize the results to other primary care populations.  The discrepancy in the prevalence of DN may attribute to the clinical setting, which was a clinic specializing in the management of diabetes.  Despite these drawbacks, these researchers demonstrated that sural nerve functions evaluated by the novel device DPNCheck were significantly associated with glycemic control and arteriosclerosis in patients with diabetes.  To ensure these associations and evaluate the effects of diabetes treatment on DN, additional studies, preferably randomized controlled trials (RCTs) that include peripheral nerve function as a primary outcome, are needed.

Hirayasu and associates (2018) noted that studies on a novel POC device (POCD) for nerve conduction study called DPNCheck have been limited to Westerners.  These investigators clarified Japanese normal limits of nerve action potential amplitude (Amp) and conduction velocity by DPNCheck (investigation I), and the validity of DPNCheck to identify diabetic symmetric sensorimotor polyneuropathy (DSPN; investigation II).  For investigation I, a total of 463 non-neuropathic Japanese participants underwent DPNCheck examinations.  Regression formulas calculating the normal limits of Amp and conduction velocity (Japanese regression formulas [JRF]) were determined by quantile regression and then compared with regression formulas of individuals from the USA (USRF).  For investigation II, in 92 Japanese diabetes patients, "probable DSPN" was diagnosed and nerve conduction abnormalities (NCA1: 1 or more abnormalities, and NCA2: 2 abnormalities in Amp and conduction velocity) were determined.  Validity of NCAs to identify "probable DSPN" was evaluated by determining sensitivity, specificity, reproducibility (kappa-coefficient) and the area under the curve of receiver operating characteristic curves.  For investigation I, JRF was different from USRF, and normal limits by JRF were higher than that of USRF.  The prevalence of Amp abnormality calculated by JRF was significantly higher than that of USRF.  For investigation II, the sensitivity, specificity and reproducibility of NCA1 and NCA2 judged from JRF were 85 %, 86 % and 0.57, and 43 %, 100 % and 0.56, respectively.  These values of JRF were higher than those of USRF.  The area under the curve of JRF (0.89) was larger than USRF (0.82).  The authors concluded that a significant difference in the normal limits of nerve conduction parameters by DPNCheck between Japanese and USA individuals was suggested; validity to identify DSPN of NCAs might improve by changing the judgment criteria from USRF to JRF.

The authors stated that the main drawback of their studies was that the number of diabetes patients was not so large (n = 92).  Thus, in order to confirm the improved accuracy to identify DPN using the POCD for NCS by using Japanese normal limits instead of USA normal limits, a larger‐scale study is needed.

Nerve Conduction Velocity in Relation to Blood Lead Levels

Yu and colleagues (2019) stated that previous studies relating nervous activity to blood lead (BL) levels have limited relevance, because over time environmental and occupational exposure substantially dropped.  These investigators examined the association of heart rate variability (HRV) and median NCV with BL using the baseline measurements collected in the Study for Promotion of Health in Recycling Lead (NCT02243904). In 328 newly hired men (mean age of 28.3 years; participation rate 82.7 %), these researchers derived HRV measures (power expressed in normalized units (nu) in the high-frequency (HF) and low-frequency (LF) domains, and LF/HF) prior to long-term occupational lead exposure.  Five-minute ECG recordings, obtained in the supine and standing positions, were analyzed by Fourier transform or auto-regressive modelling, using Cardiax software.  Motor NCV was measured at the median nerve by a hand-held device (Brevio Nerve Conduction Monitoring System, NeuMed, West Trenton, NJ).  BL was determined by inductively coupled plasma mass spectrometry.  Mean BL was 4.54 µg/dL (inter-quartile range [IQR] 2.60 to 8.90 µg/dL).  Mean supine and standing values of LF, HF and LF/HF were 50.5 and 21.1 nu and 2.63, and 59.7 and 10.9 nu and 6.31, respectively.  Orthostatic stress decreased HF and increased LF (p < 0.001); NCV averaged 3.74 m/s.  Analyses across thirds of the BL distribution and multi-variable-adjusted regression analyses failed to demonstrate any association of HRV or NCV with BL.  The authors concluded that at the exposure levels observed in this study, autonomous nervous activity and NCV were not associated with BL.

The authors stated that this study had several drawbacks.  First, findings in workers could not be extrapolated to the general population, because of the so-called healthy worker effect.  Second, although this study population was ethnically diverse, it included few Asians and no women.  Finally, a potential drawback of this study was that these investigators did not measure bone lead as an exposure marker.  Approximately 95 % of the total body burden of lead is present in the skeleton, and measurement of bone lead levels would provide a more accurate measure of the internal dose.  However, blood lead reflects both recent exogenous exposure and endogenous re-distribution of the lead stored in bone.

Nerve Conduction Studies for Cubital Tunnel Syndrome

Assmus et al (2011) stated that cubital tunnel syndrome (CubTS) is the 2nd most common peripheral nerve compression syndrome.  In German-speaking countries, CubTS is often referred to as sulcus ulnaris syndrome (retrocondylar groove syndrome).  This term is anatomically incorrect, since the site of compression comprises not only the retrocondylar groove but the cubital tunnel, which consists of 3 parts: the retrocondylar groove, partially covered by the cubital tunnel retinaculum (lig. arcuatum or Osborne ligament), the humeroulnar arcade, and the deep flexor/pronator aponeurosis.  According to Sunderland, CubTS can be differentiated into a primary form (including anterior subluxation of the ulnar nerve and compression secondary to the presence of an anconeus epitrochlearis muscle) and a secondary form caused by deformation or other processes of the elbow joint.  The clinical diagnosis is usually confirmed by nerve conduction studies.

Liu et al (2015) examined lesions' location and prognosis of cubital tunnel syndrome (CubTS) by routine motor nerve conduction studies (MNCSs) and short-segment nerve conduction studies (SSNCSs, inching test).  A total of 30 healthy subjects were included and 60 ulnar nerves were studied by inching studies for normal values; 66 patients who were diagnosed CubTS clinically were evaluated bilaterally by routine MNCSs and SSNCSs.  Follow-up for 1-year, the information of brief complaints, clinical symptoms, and physical examination were collected.  A total of 66 patients were included, 88 of nerves was abnormal by MNCS, while 105 was abnormal by the inching studies.  Medial epicondyle to 2 cm above medial epicondyle was the most common segment to be detected abnormally (59.09 %), p < 0.01; 22 patients were followed-up, 17 patients' symptoms were improved.  Most of the patients were treated with drugs and modification of bad habits.  The authors concluded that SSNCSs could detect lesions of compressive neuropathy in CubTS more precisely than the routine motor conduction studies; SSNCSs could diagnose CubTS more sensitively than routine motor conduction studies.  These investigators also found that medial epicondyle to 2 cm above the medial epicondyle was the most vulnerable place that the ulnar nerve compressed; and patients had a better prognosis who exhibited abnormal in motor nerve conduction time only, but not amplitude in compressed lesions than those who had abnormal both in velocity and amplitude.  These researchers stated that the findings of this study suggested that SSNCSs was a practical method in detecting ulnar nerve compressed neuropathy, and sensitive in diagnosing CubTS.  The compound muscle action potentials (APs) by SSNCSs may predict prognosis of CubTS.

Roberts et al (2015) noted that ulna nerve compression at the elbow is the 2nd most common neuropathy of the upper limb.  It has been suggested that nerve conduction tests are required to correctly make the diagnosis.  These researchers examined if patients with normal nerve conduction testing benefitted from surgical release of the ulna nerve.  A total of 56 patients with symptoms of ulna nerve compression at the elbow were evaluated prospectively.  All patients underwent electrophysiology testing followed by ulna nerve decompression irrespective of the results of the electrophysiology testing.  Functional scores using the Quick Disabilities of the Arm, Shoulder and Hand (DASH) and PEM score were collected up to 12 months post-surgery.  No difference was found between the group with normal and the group with abnormal electrophysiology studies.  The authors concluded that patients who clinically have ulna nerve compression still benefit from ulna nerve decompression despite normal nerve conduction tests.

Liu et al (2016) stated that the appropriate elbow position of SSNCS to diagnose CubTS is still controversial.  In a cross-sectional study, these researchers examined the effect of different elbow positions at full extension and 70° flexion on SSNCS in CubTS.  The clinical data of seventy elbows from 59 CubTS patients (between September, 2011 and December, 2014) in the Peking University First Hospital were included as CubTS group, and 30 healthy volunteers were included as the healthy group.  SSNCS were conducted in all subjects at elbow full extension and 70° elbow flexion.  Paired non-parametric test, bi-variate correlation, Bland-Altman, and Chi-squared test analysis were used to compare the effectiveness of elbow full extension and 70° flexion elbow positions on SSNCS in CubTS patients.  Data of upper limit was calculated from healthy group, and abnormal latency was judged accordingly.  CubTS group's latency and compound muscle AP (CMAP) of each segment at 70° elbow flexion by SSNCS was compared with full extension position, no statistically significant difference were found (all p > 0.05).  Latency and CMAP of each segment at elbow full extension and 70° flexion were correlated (all p < 0.01), except the latency of segment of 4 cm to 6 cm above elbow (p = 0.43), and the latency (p = 0.15) and the CMAP (p = 0.06) of segment of 2 cm to 4 cm below elbow.  Bi-variate correlation and Bland-Altman analysis proved the correlation between elbow full extension and 70° flexion.  Especially in segments across the elbow (2 cm above the elbow and 2 cm below it), latency at elbow full extension and 70° flexion were strong direct associated (r = 0.83, p < 0.01; r = 0.55, p < 0.01), and so did the CMAP (r = 0.49, p < 0.01; r = 0.72, p < 0.01).  There was no statistically significant difference in abnormality of each segment at full extension as measured by SSNCS compared with that at 70° flexion (p > 0.05, respectively).  The authors concluded that there was no statistically significant difference in the diagnosis of CubTS with the elbow at full extension compared with that at 70° flexion during SSNCS.  They suggested that elbow position at full extension can also be used during SSNCS.

Power et al (2019) noted that CubTS has a spectrum of presentations ranging from mild paresthesia to debilitating numbness and intrinsic atrophy.  Commonly, the classification of severity relies on clinical symptoms and slowing of conduction velocity across the elbow.  However, changes in CMAP amplitude more accurately reflect axonal loss.  These investigators hypothesized that CMAP amplitude would better predict functional impairment than conduction velocity alone.  A retrospective cohort of patients who underwent a surgical procedure for CubTS over a 5-year period were included in the study.  All patients had electrodiagnostic testing performed at the authors’ institution.  Clinical and electrodiagnostic variables were recorded.  The primary outcome was pre-operative functional impairment, defined by grip and key pinch strength ratios.  Multi-variable regression identified which clinical and electrodiagnostic variables predicted pre-operative functional impairment.  A total of 83 patients with a mean age of 57 years (75 % men) were included in the study.  The majority of patients (88 %) had abnormal electrodiagnostic studies; 54 % had reduced CMAP amplitude, and 79 % had slowing of conduction velocity across the elbow (recorded from the 1st dorsal interosseous).  On bi-variate analysis, older age and longer symptom duration were significantly associated (p < 0.05) with reduced CMAP amplitude and slowing of conduction velocity across the elbow, whereas body mass index (BMI), laterality, a primary surgical procedure compared with revision surgical procedure, DASH questionnaire scores, and visual analog scale (VAS) scores for pain were not.  Multi-variable regression analysis demonstrated that reduced 1st dorsal interosseous CMAP amplitude independently predicted the loss of pre-operative grip and key pinch strength and that slowed conduction velocity across the elbow did not.  The authors concluded that reduced 1st dorsal interosseous amplitude predicted pre-operative weakness in grip and key pinch strength, and isolated slowing of conduction velocity across the elbow did not; CMAP amplitude was a sensitive indicator of axonal loss and an important marker of the severity of CubTS.  It should be considered when counseling patients with regard to their prognosis and determining the necessity and timing of operative intervention.

Shubert et al (2021) stated that electrodiagnostic studies (EDX) serve a prominent role in the diagnostic work-up of CubTS; however, their reported sensitivity varies widely.  These investigators examined the sensitivity of EDX in a cohort of patients who responded well to surgical cubital tunnel release (CBTR), and whether the implementation of the Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) criteria would improve the sensitivity.  These researchers identified 118 elbows with clinical CBTS who had pre-operative EDX and underwent CBTR.  The EDX diagnoses were CubTS, ulnar neuropathy (UN), and normal ulnar nerves.  These investigators divided the 118 elbows into those that received above-elbow stimulation (XE group) and those that did not (non-XE group).  They calculated the sensitivities for all groups and re-interpreted the results according to the AANEM guidelines.  Cubital tunnel release provided significant relief in 93.6 % of the elbows.  Based on the EDX reports, 11 % patients had clear CBTS, 23 % had UN, and 66 % showed no UN.  The sensitivities were 11.7 % for CubTS and 34.2 % for any UN.  In the XE group, the sensitivity of the EDX reports for CubTS and UN climbed to 33.3 % and 58.3 %, respectively.  When the authors calculated the across-elbow motor nerve conduction velocity, the sensitivity for CubTS and UN was 87.5% and 100%, respectively.  The XE and non-XE groups showed no difference except for sex, bilaterality, concomitant carpal tunnel release, and obesity (p < 0.05).  The authors concluded that implementing AANEM guidelines resulted in significant improvement in correlation of clinical and electrodiagnostic findings of CBTS.

Liu et al (2020) noted that the 1st dorsal interosseous muscle (FDI) is usually innervated by the deep branch of the ulnar nerve; however, as was first noted by Sunderland in 1946, some individuals have variable innervation of the FDI.  These investigators examined the incidence of variable innervation of the FDI by using electrophysiological examination and further evaluated the relevance of this variation in patients with CubTS.  This study included 211 patients who underwent peripheral nerve surgery in Huashan hospital, Fudan University, between October, 2012 and February, 2014.  The patients were divided into 3 groups: the carpal tunnel syndrome (CTS) group, the CubTS group and the control group.  During surgery, electromyography (EMG) was used to determine FDI variation, and a hand function instrument was used to estimate the pinch strength between the thumb and index finger in both hands of the CubTS patients.  The EMG showed that 22 of the patients enrolled had variable innervation of the FDI.  Compared with the CTS group and the control group, the incidence of variable innervation of the FDI was much higher in the CubTS group (p < 0.05).  Patients under the age of 60 years old in the CubTS group were more likely to have the variation (p = 0.043).  A higher pinch strength ratio was significantly associated with variable innervation of the FDI in the CubTS patients (p = 0.030).  The authors concluded that by means of EMG, the findings of this study demonstrated that the variable innervation of the FDI could be innervated by the median nerve.  In the CubTS patients, the higher incidence of FDI variation was possibly related to age, and this variation might lead to a better prognosis for CubTS patients.

Furthermore, an UpToDate review on “Ulnar neuropathy at the elbow and wrist” (Doherty, 2021) states that “Electrodiagnostic testing, typically involving nerve conduction studies and sometimes needle electromyography (EMG), is a standard part of the evaluation for ulnar neuropathy, even in seemingly straightforward cases where suspicion is high.  These tests are useful to confirm the diagnosis, establish baseline results, determine severity, and rule out other potential causes.  They are particularly helpful when the clinical presentation is not straightforward, such as in cases complicated by associated musculoskeletal pain, coexisting carpal tunnel syndrome, or radiculopathy”.

Pre-Operative Electrodiagnostic Studies for Prediction of Post-Operative Outcomes in Ulnar Neuropathy at the Elbow    

In a systematic review, Meiling et al (2023) examined the association between pre-operative EDX studies and post-operative pain and functional outcomes following ulnar nerve decompression and/or transposition for ulnar neuropathy at the elbow (UNE).  Database search was carried out by an experienced librarian of all available studies in the English language from 1990 to June 8, 2022.  Databases included Ovid Medline (R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily, Ovid Embase, Ovid Cochrane Central Register of Controlled Trials, and Scopus.  Inclusion criteria consisted of RCTs, prospective and retrospective longitudinal studies, and studies involving adults 18 years of age or older who underwent ulnar nerve decompression and/or transposition for the treatment of UNE.  Study quality and risk of bias were assessed using the National Heart, Lung, and Blood Institute (NHLBI) Study Quality of Assessment Tool.  Certainty in evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.  A meta-analysis was not performed.  A total of 289 studies were screened, and 8 retrospective cohort studies met inclusion criteria comprising 762 patients.  A decreased or absent pre-operative sensory nerve action potential amplitude (SNAP) showed significance with worse post-operative outcomes.  The presence of pre-operative conduction block showed significance in higher quality studies.  There was limited evidence for slow pre-operative motor conduction velocities or pre-operative EMG abnormalities and post-operative outcomes.  Overall quality assessment indicated that 2 studies had "good", 4 "fair" and 2 "poor" quality of evidence.  Certainty in evidence was "low" due to risk of bias.  The authors concluded that a decreased or absent pre-operative ulnar SNAP may predict worse post-operative outcomes.  Per higher quality studies, pre-operative conduction block at the elbow may also predict worse post-operative outcomes.  These researchers stated that careful interpretation is needed with a full understanding of the limited evidence, risk of bias, and low certainty in evidence to support the use of pre-operative EDX to predict post-operative outcomes in UNE.

Appendix

Documentation Requirements

The member's medical records must clearly document the medical necessity for the test. It is not necessary to include documentation with each claim submission. Data gathered during NCS, however, should be available which reflect the actual numbers (latency, amplitude, etc.), preferably in a tabular (not narrative) format. The reason for referral and a clear diagnostic impression are required for each study. In cases where a review becomes necessary, either a hard copy of waveforms or a complete written report with an interpretation of the test must be submitted upon request.

Normal findings and abnormalities uncovered during the study should be documented with the muscles tested, the presence and type of spontaneous activity, as well as the characteristics of the voluntary unit potentials and interpretation.

References