The Role of Ultrasound in Nerve Conduction Studies

Ultrasound can be used during nerve conduction studies to better localize the nerve in question at the site of stimulation or recording.^1,2 The accuracy of near-nerve needle stimulation or recording is increased when nerves and surrounding structures are imaged and needles are placed under ultrasound guidance. Ultrasound-guided needle placement is a relatively easy technical skill to develop. Formal training courses are available with hands-on demonstration sessions, and the technique can be refined using fresh frozen cadavers or gel phantoms with enclosed targets for simulation of image-guided needle placement (Box 12.1). Once this skill is acquired, it facilitates the use of ultrasound as a complement to electrodiagnosis by enhancing the accuracy and safety of the invasive aspects of nerve conduction studies and needle EMG.

Ultrasound-guided needle placement can be very helpful in certain situations in the EMG laboratory. When apparent conduction block on a motor nerve conduction study is encountered but it is not clear whether technical factors such as submaximal stimulation may be contributing, a monopolar needle can be placed adjacent to the nerve, under ultrasound guidance, to allow for supramaximal stimulation (at much lower levels of current than required with surface stimulation). There are many potential applications for this, usually in nerves that are deeper and more difficult to stimulate with surface electrodes. Examples include the radial nerve at the spiral groove or elbow (Fig. 12.1), the sciatic nerve in the thigh, the tibial nerve at the knee, the femoral nerve in the proximal thigh, or even the brachial plexus or exiting cervical roots (Fig. 12.2).³ Femoral nerve stimulation may be indicated in cases of diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) and select cases of Lambert-Eaton myasthenic syndrome, in which case repetitive stimulation before and after isometric exercise is necessary. In such cases, the neurovascular bundle is easily visualized with ultrasound and the needle can be placed directly adjacent to the nerve, allowing for less current, better patient comfort, and a technically superior response (Fig. 12.3). Such procedures can be also be more safely performed in anticoagulated patients, because the needle can be placed under direct ultrasound guidance, with visualization of nearby vascular structures facilitated by the use of color Doppler. The availability of ultrasound in this setting also allows for monitoring for hematoma formation after the needle is removed.

Fig. 12.1 Example of near-nerve stimulation facilitated by the use of ultrasound guidance to place the needle (down arrows) directly adjacent to the radial nerve at the spiral groove (arrow). Near-nerve stimulation can be used to exclude pseudo-conduction block secondary to submaximal surface stimulation.

Fig. 12.2 Short axis scan of the three trunks of the brachial plexus in the supraclavicular fossa (arrows). AS, Anterior scalene.

Fig. 12.3 Image of the femoral nerve (FN) with adjacent femoral artery (FA) to the left and iliopsoas muscle (IP) to the right.

Ultrasound can also facilitate nerve conduction studies in challenging cases in which anatomy is altered or usual landmarks are not palpable as a result of body habitus or dysmorphism. In such cases, the nerve of interest can be localized ultrasonographically prior to proceeding with standard surface stimulation, for example, after ulnar nerve transposition surgery in which the altered position of the nerve can be mapped out in the antecubital fossa and inching studies performed along the actual course of the nerve.

Ultrasound-guided nerve conduction techniques have been described to allow more accurate and reliable evaluation of nerves that previously had been difficult to study for technical or anatomic reasons. Examples include the lateral femoral cutaneous nerve in the proximal thigh and the saphenous nerve in the calf. Bailey and associates reported on a cohort of 50 normal subjects, including many with body mass indices in the obese range, in which the lateral femoral cutaneous nerve was localized with ultrasound, approximately 11 cm distal to the stimulation site at the inguinal crease (Fig. 12.4). The G1 electrode was placed directly over the nerve, and responses were elicited in 49 of 50 patients, with an average amplitude of 9.3 μV and side-to-side variability of 34%.⁴ Similarly, the saphenous nerve can be easily identified with ultrasound in the proximal calf and followed distally, to allow for placement of recording or stimulating electrodes directly over the nerve.⁵ If no response is obtained on standard conduction studies and there is a question as to whether technical factors may be contributing, it is simple to examine the limb with ultrasound and identify the nerve of interest, to ensure setup is optimal. In critical cases placing a needle next to the nerve for either stimulating or recording can be performed when necessary.

Fig. 12.4 Picture of the lateral femoral cutaneous nerve (LFCN) in the proximal thigh, showing the typical “eye” appearance with the highly echogenic nerve surrounded by an envelope of hypoechoic fat.

Imaging of Nerve

Ultrasound imaging of nerve is rapidly emerging as a useful diagnostic technique. In cases of entrapment neuropathy, electrodiagnosis helps to determine the presence and severity of entrapment, and to distinguish demyelination from axonal loss, but no information regarding the underlying cause can be elicited. Ultrasound can identify underlying space-occupying or compressive lesions such as lipoma, fibroma, hemangioma, hematoma, amyloid, synovitis, tenosynovitis, ganglion cyst, intraneural ganglion, pseudoaneurysm, anomalous muscle, and primary nerve tumors including neurofibromas, schwannomas, malignant nerve sheath tumors, and pericytomas.^6–8 Typical sites of entrapment that can be evaluated with ultrasound are listed in Table 12.1.

Table 12.1 Common Sites of Entrapment that Can Be Evaluated with Ultrasound

∗ The sciatic nerve can be difficult to visualize in the buttock/posterior hip region without the use of a curvilinear probe, particularly in obese patients.

Padua and colleagues used ultrasound imaging in a series of 77 cases presenting to the EMG laboratory with various mononeuropathies, including peroneal neuropathy at the fibular head, ulnar neuropathy at the elbow, and atypical median neuropathy at the wrist. In 26% of cases, an underlying cause for the neuropathy was identified on ultrasound, which led to an alteration in the management of those cases.⁸ Visser found intraneural ganglion cysts on ultrasound in 18% of patients with electrophysiologic evidence of common peroneal neuropathy at the fibular head.⁹ Similarly, in cases of suprascapular neuropathy, ultrasound of the posterior shoulder may identify a spinoglenoid cyst.¹⁰ In a series of 77 patients (96 wrists) with clinical and electrophysiologic evidence of carpal tunnel syndrome, without typical risk factors such as rheumatoid arthritis, diabetes, or pregnancy, 17% had evidence of underlying flexor tenosynovitis on ultrasound, which has implications with regard to management in comparison with cases of idiopathic carpal tunnel syndrome.⁷ Nakamichi and Tachibana showed that in patients presenting with unilateral carpal tunnel syndrome, 35% had an underlying structural abnormality, which altered the management in those cases.¹¹ Anatomic variants, such as a bifid median nerve or persistent median artery, are easily identified on ultrasound and can have surgical implications, particularly with use of an endoscopic surgical technique, arguing for routine preoperative ultrasonography.

Ultrasound imaging is also useful in detecting complete nerve transection, which can be particularly helpful acutely, when electrodiagnostic studies cannot differentiate between conduction block and axonal injury.¹² Neuromas can be easily identified on ultrasound. In addition, sonopalpation (direct pressure from the transducer applied over the area of interest) can be used to determine if a neuroma is symptomatic.¹³ Dynamic imaging is also useful in the diagnosis of various nerve disorders. For example, one can confirm the presence of a subluxing ulnar nerve, but more importantly, evaluate for a snapping head of the medial triceps, an entity that commonly accompanies a symptomatic subluxing ulnar nerve, and if unrecognized, can lead to a poor surgical outcome.^14–15

When diagnosing nerve entrapment per se, as opposed to the underlying cause of the entrapment, there is a need for more studies evaluating both normal controls, diseased controls, and those with the entrapment of interest to delineate more accurately normal cross-sectional areas, the most appropriate site for measurement, the utility of patient-derived control measurements,^16,17 and the effects of various body metrics on the normal values. Normal values for a number of nerves have been published.¹⁸ In particular, a number of studies have focused on median neuropathy at the wrist and ulnar neuropathy at the elbow with considerable overlap demonstrated between normal controls and those with the disease.^7,14,18–22

Clinical Application—Case 1

A 53-year-old man presented with a 6-month history of progressive pain during and after soccer games, progressing to pain and mild ankle weakness when hiking, that was unresponsive to antiinflammatory medication. On examination, the patient was noted to have mild to moderate weakness of ankle dorsiflexors and toe extensors on the affected side. Nerve conduction studies and needle examination demonstrated a common peroneal neuropathy, without focal conduction block or slowing (Tables 12.2 and 12.3). Ultrasound of the peroneal nerve showed a large intraneural ganglion cyst that was surgically decompressed (Fig. 12.5).

Table 12.2 Findings for Case 1: Nerve Conduction Studies

Table 12:3 Findings for Case 1: Electromyography

Fig. 12.5 Peroneal intraneural ganglion cyst (arrow) within the peroneal nerve, causing common peroneal neuropathy.

Intraneural ganglion cysts involving the peroneal nerve arise from the proximal tibiofibular joint, caused by communication via the intraarticular branch of the peroneal nerve. Typically patients have pain and fluctuating weakness (worse with prolonged weightbearing), as opposed to more typical peroneal neuropathies associated with weight loss, habitual leg crossing, and frequent squatting, which tend to be painless and are more frequently associated with conduction block on nerve conduction studies.²³ It is important to differentiate these etiologies because surgical intervention is indicated in intraneural ganglion cysts as opposed to the natural history of spontaneous improvement with other causes of peroneal neuropathy.

The Role of Ultrasound in Needle EMG

There are many potential applications of ultrasound with respect to accurate identification of muscle during needle EMG. In select circumstances ultrasound enhances the accuracy and safety of needle EMG. Several cadaveric studies evaluated the accuracy of non–image-guided needle placement in the hands of experienced electromyographers, with accuracy ranging from 0% to 83% depending on the muscle examined.^24–26 The authors evaluated the accuracy of nonguided versus ultrasound-guided EMG needle placement in 14 different muscles in the lower limb in fresh frozen cadavers and found overall nonguided accuracy rates of 50% for a fully trained resident electromyographer compared with 83% for an experienced staff electromyographer at a large academic EMG laboratory. With the use of ultrasound guidance, accuracy rates were markedly enhanced, with improvement to 96%.

Although cadaveric studies are limited by the lack of usual feedback such as muscle insertional activity, motor unit activation, and inability to palpate the contacting muscle, there are clinical parallels in which such feedback is not available. Examples include unresponsive or uncooperative patients, obese patients, or those with severe denervation or spasticity preventing voluntary activation of the muscle of interest. In addition, ultrasound is particularly useful when examining muscles that are not easily activated in isolation or when agonist muscles may have different innervation. Examples include the median and ulnar innervated portions of the flexor digitorum profundus muscle; the rhomboid muscle, which can be confused with the overlying trapezius; and the iliopsoas, in which the needle may be mistakenly placed in the other hip flexors (e.g., rectus femoris or sartorius). Muscle localization is also a challenge when the normal anatomy is altered by trauma or surgery, or when typical anatomic landmarks are absent (obese patients). Some examples in the authors’ experience include a case in which the flexor carpi ulnaris muscle had been moved during ulnar transposition surgery, another case in which the flexor pollicis longus muscle was difficult to identify with palpation because of multiple prior surgeries on the tendon, and cases of muscle transfer in association with brachial plexus or other nerve reconstruction surgery.

Ultrasound guidance may be indicated more frequently for accurate muscle localization in less experienced electromyographers; however, it can also be a very useful tool even for experienced physicians when examining deeper muscles, unfamiliar muscles not examined on a regular basis (for example the popliteus), or muscles that are in proximity to vital structures such as the diaphragm or chest wall muscles. Ultrasound-guided needle examination may also be indicated in other higher-risk situations such as the anticoagulated patient, in whom examination of certain muscles such as iliopsoas, flexor pollicis longus, or posterior tibialis is necessary. Most machines are equipped with power Doppler, which can be a useful tool to identify nearby vascular structures that one should avoid. Ultrasound can also be used for postprocedural surveillance after a higher-risk muscle has been needled or when there has been evidence of bleeding at the time of needle examination, to examine for a developing hematoma.

EMG guidance has been used to allow accurate injection of chemodenervating agents for many years, but the addition of ultrasound may be complementary or in some cases can be used in place of EMG guidance. When targeting small muscles in a very spastic or dystonic limb, the patient will be unable to selectively activate and ultrasound can provide excellent anatomic localization. Also, when targeting muscles in proximity to vital structures, such as the scalenes, subclavius, and pectoralis minor muscles when treating myofascial pain with associated thoracic outlet symptoms, the use of power Doppler and visualization of the brachial plexus significantly enhances safety (Fig. 12.6)²⁷ (further discussion of ultrasound-guided injections can be found in Chapter 11).

Fig. 12.6 Image of the anterior scalene (AS) and middle scalene (MS) in proximity to the brachial plexus (BP) and vessels including the subclavian artery (SA). When targeting the scalenes for chemodenervation, the needle can be placed under ultrasound guidance to avoid damage to nearby neurovascular structures. SCM, Sternocleidomastoid.

Needle Examination of the Diaphragm with Ultrasound

The diaphragm can be easily visualized in most patients using a high-frequency (13-8 MHz) linear array transducer, although in larger patients the authors have found a cardiac curvilinear probe useful because it provides better visualization of the diaphragm at greater depths. The linear probe is placed perpendicular to the lower ribs, at approximately the anterior axillary line, spanning two ribs. The ribs are easily identified by the bright signal generated by the bony cortex, and the intercostal muscles are seen between the ribs, with subcutaneous tissue superficial and diaphragm muscle layer deep to the intercostal muscles (Fig. 12.7). Deep to the diaphragm the liver can be identified, because of a more homogeneous, nonfibrillar appearance, punctuated by small blood vessels. The diaphragm is identified by its location, activation pattern (contraction/thickening with inspiration), curved appearance in some cases, and displacement by pleura and/or lung tissue coming into the field of view with end inspiration (Fig. 12.8).

Fig. 12.7 Ultrasound-guided needle examination of the diaphragm. The transducer is initially placed perpendicular to the ribs, and the different layers of tissue are identified: subcutaneous tissue, two layers of intercostal muscle spanning the two ribs, and the diaphragm.

Fig. 12.8 After identification of the anatomy perpendicular to the long axis of the ribs, the transducer is aligned parallel to the ribs overlying the intercostal space. If the patient takes a deep inspiration, the bright shadow of the lung will be seen coming into the field of view from the superolateral direction, displacing the diaphragm and underlying liver.

Once the diaphragm is identified, the transducer is then turned 90 degrees, parallel to the ribs, overlying one of the lowest intercostal spaces (usually the seventh or eighth space is targeted). The needle can then be inserted using a long axis approach (i.e., the needle is inserted parallel and deep to the transducer; Fig. 12.9), with the entry point medial to the transducer, thereby positioning the lung farthest from the needle. These authors have found that when the diaphragm is deeper, in larger patients, an oblique standoff approach allows one to visualize the needle easily. This technique uses heaped up gel beneath one end of the transducer (at the site of needle entry), so that the transducer is parallel with the needle as it is inserted obliquely through the heaped up gel and into the chest wall. Motor units in the diaphragm fire during inspiration and tend to be shorter duration and more rapidly recruited than motor units in the intercostal or limb muscles. Sharp pain during needle examination usually occurs with penetration of rib periosteum, pleura, or peritoneum, with dull aching discomfort sometimes experienced when the needle is in the diaphragm itself.

Fig. 12.9 Approach used for image guided needle placement for electromyography (EMG) of the diaphragm. (Patient’s head is to the left of the image). The needle is inserted parallel to the long axis of the transducer, using a medial to lateral approach. The lowest intercostal space in which a needle can be inserted is usually attempted first. Ultrasound can confirm the best intercostal space with maximal diaphragm thickness and minimal lung encroachment.

Indications for diaphragm needle EMG include failure to wean, unexplained dyspnea, identification of the underlying pathophysiology of neuromuscular respiratory failure (differentiating muscle, nerve, and neuromuscular junction disorders), and providing prognostic information in cases of phrenic neuropathy. Needle EMG is typically performed without image guidance, but risks include pneumothorax, penetration of abdominal viscera, and hemorrhage (particularly in patients with bleeding tendency). Because of these risks, needle examination may be suboptimal, with failure to actually enter the diaphragm particularly in more challenging cases such as obese patients, patients with altered anatomy or advanced chronic obstructive pulmonary disease (COPD) in whom the lungs are hyperinflated and may lie lower than usual, and in cases of severe denervation or atrophy, in which there may be little muscle to target and/or lack of usual auditory feedback (firing of motor units) to guide needle placement.

Ultrasound guidance can enhance the safety and accuracy of the needle examination of the diaphragm. Even in relatively straightforward cases, the optimal intercostal space for needle entry (where the diaphragm is thickest and there is little or no encroachment of the lung during inspiration) can be identified, and the depth of the diaphragm is noted. Thus if one is using a standard nonguided technique as described by Bolton and colleagues,²⁹ with needle insertion perpendicular to the skin/chest wall (Fig. 12.10), knowing the anticipated depth of the diaphragm is helpful. In more difficult patients, direct visualization of the needle with ultrasound throughout insertion can minimize risk and maximize the chance of entering the diaphragm. An additional advantage of ultrasonographic evaluation of the diaphragm is evaluation of function. Is the muscle contracting with inspiration? Is it contracting with phrenic nerve stimulation? What is the quality of motion? Normal values for diaphragm muscle thickness at end inspiration and expiration are not available but with the development of such data, ultrasound may be able to provide additional diagnostic information noninvasively in the future.

Fig. 12.10 Diagram showing one of the more commonly used techniques for standard or nonguided needle examination of the diaphragm. The needle is inserted perpendicular to the chest wall, at the lowest possible intercostal space, as far anterior as possible, and will pass through two layers of chest wall muscle before encountering the diaphragm, which should activate with inspiration only. EMG, Electromyography.

The greatest concern when performing needle EMG of the diaphragm is pneumothorax. However, in practice, relative risk of this is very low with examination of the diaphragm, and in fact pneumothorax is more likely to occur as a complication of needle examination of chest wall muscles such as serratus anterior, rhomboid, and thoracic paraspinal muscles. Ultrasound can similarly be used to localize these muscles particularly in obese subjects in whom ribs and other anatomic landmarks cannot be palpated, ensure accuracy (because most chest wall muscles cannot be activated in isolation), and evaluate qualitatively for atrophy or signs of denervation in cases in which needle examination is technically difficult or contraindicated (Fig. 12.11). In cases of unilateral disease, the patient can serve as his or her own control with comparing with the contralateral side.

Fig. 12.11 Chest wall muscles are easily identified with ultrasound, facilitating accurate needle placement and minimizing the risk in complicated cases. The rhomboid and trapezius muscles are easily differentiated.

Clinical Pearl

When performing ultrasound-guided needle examination, if a short axis approach is used (Fig. 12.12), the tip of the needle will appear almost identical to the midshaft of the needle (i.e. a bright, hyperechoic spot on the screen). Therefore, as soon as the needle tip is identified, advancement of the needle must stop while the ultrasound probe is repositioned to allow re-identification of the needle tip as it is advanced deeper.

Fig. 12.12 Images depicting long-axis and short-axis techniques for needle placement. If using the short-axis approach, when the needle tip is directly under the transducer it will appear as a bright spot in the image, but if the needle is advanced farther without moving the transducer, the midshaft of the needle will now be imaged but the appearance will be almost identical and can be mistaken for the needle tip.

Risk of Needle EMG in Anticoagulated Patients

The availability of portable, high-resolution ultrasonography in the authors’ laboratory has allowed for modifications in practice related to anticoagulation. To date, the literature has been sparse in relation to this issue, with scattered case reports of compartment syndromes and hematomas, the majority in nonanticoagulated patients.^30–35 One study by Caress and associates in which MRIs were reviewed from 17 patients who underwent EMG of the paraspinal muscles followed by MRI, found small subclinical hematomas in 5 out of 45 paraspinal muscles on retrospective review.³⁶ This study has led to widespread teaching that paraspinal muscles should not be examined in anticoagulated patients. There was also a survey of 47 electrodiagnostic laboratories in which four laboratories reported via retrospective recall at least one case of bleeding in anticoagulated patients requiring medical or surgical intervention. Based on the available literature, many EMG laboratories have required patients to discontinue warfarin before undergoing EMG, a practice that is controversial given the relative risk of discontinuing anticoagulation as it relates to stroke.³⁷

These authors evaluated more than 200 patients, of whom one half were anticoagulated with warfarin, who underwent EMG of the tibialis anterior muscle.³⁸ Ultrasound examination of the tibialis anterior muscle was performed shortly after the needle EMG to examine for hematoma development. Three very small hematomas were identified, two in patients taking warfarin and one in a patient on aspirin and nonsteroidal antiinflammatory (NSAID) medication. None of the hematomas was clinically evident, and the authors concluded that there was no increased risk of significant bleeding after needle EMG of the tibialis anterior in anticoagulated patients. Based on the results of this study, with larger numbers of data currently being collected, these authors changed their practice such that patients are no longer required to discontinue anticoagulation prior to needle EMG, although the upper limit of INR and the specific muscles examined are determined by the individual electromyographer performing the study. Other laboratories across the United States have since changed their laboratories practices to avoid temporary cessation of anticoagulation prior to needle EMG based on the results of this study. This is one example of how the availability of high-resolution ultrasonography in the EMG laboratories setting can lead to improvements in quality and safety.

Imaging of Muscle

Ultrasound imaging is a useful adjunct during the electrodiagnostic evaluation of muscle. In addition to localizing specific muscles, diagnostic information can be elicited regarding muscle size, presence of atrophy or hypertrophy (assuming normal values have been established), changes in echo-texture, patterns of muscle involvement, and assessment of muscle function both with voluntary activation and in response to electrical stimulation. Musculoskeletal causes for pain such as lateral epicondylitis or rotator cuff tendinitis can be evaluated concomitantly, after excluding a neuromuscular etiology for the symptoms, if the electromyographer also has training in diagnostic musculoskeletal ultrasound.

Ultrasound has high sensitivity in screening for neuromuscular disease,^39–41 with 87% to 92% sensitivity demonstrated by some investigators, and as such this can be a very useful tool in the pediatric population in whom standard electrodiagnostic evaluation can be challenging. Visual evaluation of gray scale signal on ultrasound has significant inter- and intrarater variability; as a result, gray scale imaging via quantification of muscle echogenicity has been developed as a more reliable means of identifying changes in homogeneity as well as overall echo-texture.⁴² Muscle ultrasound was able to differentiate between neurogenic and myopathic disorders in 92% of hypotonic infants in one study.⁴³

Quantitative gray scale imaging is discussed in more detail elsewhere in this text (see Chapters 3 and 10), including current limitations that need to be taken into consideration, including the need for normal values for different ultrasound machines (using the same anatomic landmarks and standardized muscle position), and the necessity of maintaining consistent machine settings for serial examinations. System settings adjustments for each machine as well as correction models may allow for transposition of normal values to different machines in the future but such software is not yet commercially available. There certainly appears to be a role in targeting muscle biopsy if heterogeneity or atrophy can be recognized. This could address the issue of inadvertently selecting very severely involved muscles, which may give nonspecific findings on biopsy, and avoid biopsy of an uninvolved muscle.

Clinical Application—Case 4

A 53-year-old-man was noted to have a swollen, painful, erythematous left leg after undergoing brachial plexus reconstruction surgery. The working diagnosis was cellulitis but there was no immediate response to intravenous antibiotic therapy and NSAID medication. Once he started mobilizing, he was noted to have significant weakness of ankle dorsiflexors and toe extensors with associated footdrop. At follow-up 2 months later, he was referred for electrodiagnostic evaluation because of persistent footdrop.

Nerve conduction studies and needle examination are presented in Tables 12.4 and 12.5. The resident performing the study had a working diagnosis of peroneal neuropathy based on the clinical presentation and findings on nerve conduction studies. However, he was surprised by the needle EMG findings of decreased insertional activity and no motor unit activation in the tibialis anterior, particularly given the presence of compound muscle action potentials, albeit small, in the peroneal distribution. The attending physician repeated the needle examination of select muscles and noted similar findings in the tibialis anterior but did find fibrillation potentials and small motor unit potentials more laterally in that muscle, as well as in the peroneus longus and extensor hallucis longus muscles.

Table 12.4 Findings for Case 4: Nerve Conduction Studies

Table 12.5 Findings for Case 4: Electromyography

With palpation, the tibialis anterior muscle was noted to feel fibrotic. It was decided to evaluate the muscle with ultrasound, and there was clear change in muscle architecture, with loss of the normal fibrillar pattern and increase in echogenicity. Findings were patchy and not consistent throughout the entire muscle (Fig. 12.13). Based on the combination of ultrasound and electrodiagnostic findings, in the clinical context of onset of painful red swollen leg after an 11-hour brachial plexus surgery, unresponsive to antibiotics, the patient was diagnosed with direct muscle crush injury, without evidence of peroneal neuropathy.

Fig. 12.13 Ultrasound image of the anterior tibialis (AT) muscle in a patient who underwent an 11-hour brachial plexus surgery and woke up with footdrop. The muscle has lost the normal heterogeneous, starry night appearance and appears fibrotic, both clinically and electrophysiologically.

The Role of Ultrasound in Education

Because of the portability of ultrasound, this imaging modality can be used in many different settings, including the EMG laboratory, the operating room, the intensive care unit, and the classroom. With regard to education, there is a potential role for improved needle EMG accuracy, by visualization of the functional anatomy: the depth of the muscle, the direction of the muscle fibers, the location of the musculotendinous junction, the pattern of contraction, as well as neighboring muscles that might be inadvertently targeted in error and the proximity of adjacent neurovascular structures.

Conclusion

Ultrasound provides high-resolution soft tissue imaging that is easily accessible, fast, relatively cost effective, and safe. It can enhance the accuracy and safety of the clinical neurophysiology examination while providing additional structural and functional information. For these reasons, it is an ideal complementary tool that can significantly enhance the electrodiagnostic evaluation, and as the field develops, with more literature to support the role of high-resolution ultrasonography in the diagnosis of nerve and muscle disease, the authors foresee that high-frequency diagnostic ultrasound will become an integral component of the standard electrodiagnostic evaluation.