In the electromyography (EMG) laboratory, the radial nerve is studied less frequently than the median and ulnar nerves and their respective well-known lesions. Nevertheless, entrapment of the radial nerve does occur, often affecting the main radial nerve either in the upper arm or axilla. Isolated lesions of its terminal divisions in the forearm, the posterior interosseous, and superficial radial sensory nerves, also occur. Although radial motor…

Ulnar neuropathy at the wrist (UNW) is a rare condition that sometimes is confused with ulnar neuropathy at the elbow (UNE) or, more often, with early motor neuron disease. Knowledge of the detailed anatomy of the ulnar nerve at the wrist is necessary to understand the several unique clinical and electrophysiologic patterns that can occur with UNW ( Fig. 23.1 ). The differential diagnosis is limited…

Ulnar neuropathy at the elbow (UNE) is second only to median nerve entrapment at the wrist (i.e., carpal tunnel syndrome [CTS]) as the most common entrapment neuropathy affecting the upper extremity. In contrast to CTS, localizing the site of the lesion by electrodiagnostic (EDX) studies often is much more difficult in patients with ulnar neuropathy. Indeed, the diagnosis of a nonlocalizable ulnar neuropathy is not infrequently…

Proximal median neuropathy is distinctly uncommon compared with median nerve entrapment at the carpal tunnel. Differentiating between median neuropathy at the wrist and more proximal entrapments can be difficult based on clinical grounds alone, especially in mild cases. Electrodiagnostic (EDX) testing plays a key role in localizing the lesion in these unusual cases, especially if the lesion results from trauma or compression. In addition, neuromuscular ultrasound…

Median nerve entrapment at the wrist is the most common of all entrapment neuropathies and, consequently, is one of the most frequent reasons for referral for an electrodiagnostic (EDX) study. In nearly all patients, the usual site of compression occurs in the carpal tunnel and results in a constellation of symptoms and signs known as the carpal tunnel syndrome (CTS). Lesions of the C6–C7 nerve roots…

Although neuromuscular ultrasound has been used mostly in mononeuropathies, there are also some specific advantages to using it in selected polyneuropathies, motor neuron disorders, and myopathies. In this chapter, we summarize the basic ultrasound assessments that can be done in these disorders, with more specific findings discussed in the various clinical chapters that follow. Just as in mononeuropathies, neuromuscular ultrasound should be used as a complement…

One of the most common and useful applications of neuromuscular ultrasound is in the evaluation of mononeuropathies. Although mononeuropathies often result from entrapment of isolated peripheral nerves within specific anatomic fibro-osseous canals, there are a variety of other causes, many of which are structural in nature and can be easily visualized on ultrasound. Usually, a combination of clinical examination supplemented by electrodiagnostic (EDX) studies allows one…

In previous editions of this textbook, one did not find any mention of neuromuscular ultrasound. However, since the last edition, much has changed in the field of neuromuscular medicine. The value of neuromuscular ultrasound in the evaluation of patients with various neuromuscular conditions is now well established. It is an invaluable tool whose use will undoubtedly continue to expand in the future. Neuromuscular ultrasound is a…

The value of information gained from electrodiagnostic studies relies on correct data collection and, even more importantly, correct data interpretation. Mastering the technical aspects of routine nerve conduction studies (NCSs) and electromyography (EMG) usually can be accomplished within several months to 1 year. However, if appropriate studies have not been chosen for the particular clinical situation or if interpretation of any of the studies is faulty,…

After assessment of insertional and spontaneous activity, the needle electromyography (EMG) examination moves on to the evaluation of motor unit action potentials (MUAPs). In a process similar to the analysis of spontaneous activity, MUAPs must be assessed for morphology (duration, amplitude, phases), stability, and firing characteristics. The pattern of MUAP abnormalities that emerges from this part of the examination usually will allow a determination of whether…

The analysis of spontaneous activity is the first part of the needle electromyography (EMG) examination of every muscle. The presence of abnormal spontaneous activity on EMG is of key importance and yields several important pieces of information. First, the distribution of abnormal spontaneous activity often indicates the neuroanatomic localization of the lesion. For example, in an isolated radiculopathy, denervation potentials are restricted to muscles in the…

Upper Extremity Median Nerve Abductor Pollicis Brevis (APB) ( Fig. 13.1A,B ) Innervation Median nerve, medial cord, lower trunk, C8–T1 Needle Insertion Insert the needle tangentially into the lateral thenar eminence, just lateral to the mid-point of the first metacarpal. Activation Abduct the thumb with arm and hand in the supinated position. Key Clinical Points The APB is the best median muscle to sample distal to…

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Tibial Motor Study ( Fig. 11.1 ) Recording Site Abductor hallucis brevis (AHB) muscle: G1 placed 1 cm proximal and 1 cm inferior to the navicular prominence G2 placed over the metatarsal-phalangeal joint of the great toe Stimulation Sites Medial ankle: Slightly proximal and posterior to the medial malleolus Popliteal fossa: Mid-posterior knee over the popliteal pulse Distal Distance 9 cm Key Points The tibial compound…

Median Motor Study ( Fig. 10.1 ) Recording Site Abductor pollicis brevis (APB) muscle (lateral thenar eminence): G1 placed over the muscle belly G2 placed over the first metacarpal-phalangeal joint Stimulation Sites Wrist: Slightly lateral to the mid-wrist between the tendons to the flexor carpi radialis and palmaris longus Antecubital fossa: Just medial to the brachial artery pulse Distal Distance 7 cm Key Points The study…

For every electrodiagnostic (EDX) test performed, one needs to decide if the study is normal or abnormal. That determination often needs to be made in real time as the testing progresses, so that the study can be modified based on new information obtained as the testing proceeds. However, interpreting a test as normal or abnormal is not always straightforward and requires some understanding of basic statistics.…

Understanding and recognizing artifacts and technical factors play a central role in every nerve conduction and electromyography (EMG) study ( Box 8.1 ). The value of the information gained during an electrodiagnostic (EDX) study relies on two important and complementary processes: (1) collecting the data correctly and (2) interpreting the data correctly. If the collected data are not technically accurate, then correct interpretation of the data…

Although peripheral nerve anatomy is more or less similar among individuals, in a sizable minority, there are some significant anatomic variations. These are known as anomalous innervations. Several of these anomalous innervations of peripheral nerve are commonly seen in the electromyography (EMG) laboratory. It is critical that every electromyographer be able to identify them during routine nerve conduction studies. If these anomalies are not recognized, they…

The use of repetitive nerve stimulation (RNS) dates to the late 1800s, when Jolly made visual observations of muscle movement that occurred after nerve stimulation. Although his initial studies were done with submaximal stimuli and mechanical rather than electrical measurements were made, Jolly noted a decrementing response following RNS in patients with myasthenia gravis and correctly concluded that the disorder was peripheral. Subsequently, RNS has been…

Few routine electrophysiologic tests are available to evaluate the cranial nerves and their proximal segments other than visual and brainstem-evoked potentials. However, cranial nerves V (trigeminal) and VII (facial), along with their connections in the pons and medulla, can be assessed electrically with the blink reflex. The blink reflex is essentially the electrical correlate of the clinically evoked corneal reflex. Like the H reflex, the blink…