Nerve Conduction Studies: Normal Adult Values Upper Extremity Studies Motor Studies Nerve Record Amplitude (mV) Conduction Velocity (m/s) Distal Latency (ms) Distal Distance (cm) Median Abductor pollicis brevis (APB) ≥4.0 ≥49 ≤4.4 7 Ulnar Abductor digiti minimi (ADM) ≥6.0 ≥49 ≤3.3 7 Ulnar First dorsal interosseous (FDI) ≥7.0 ≥49 ≤4.5 Variable (8–12 a ) Radial Extensor indicis proprius (EIP) ≥2.0 ≥49 ≤2.9 4–6 a Distance measured…

Electrodiagnostic (EDX) studies are generally well tolerated and rarely associated with any significant side effects. Most nerve conduction studies (NCSs) use surface stimulating and recording electrodes, which are not invasive. However, electrical current is applied to the patient when stimulating peripheral nerves. In patients with pacemakers, cardioverter-defibrillators, and other similar cardiac devices, this current may pose a risk under certain situations. In contrast, needle EMG is…

In the office, hospital, and home, we are surrounded by equipment, appliances, and many other devices powered by electricity. Although knowledge of electricity and electronics is not needed to watch television, talk on the telephone, or use a toaster, these examples are just the tip of the electrical and electronic iceberg in the world we live in as electromyographers. One might ask, is it really necessary…

In conjunction with the clinical examination, electrodiagnostic (EDX) studies frequently play a key role in the evaluation of neuromuscular disorders in infants and children. Indeed, there are a large number of neuromuscular disorders that present in the pediatric age group. In many of these cases, EDX studies are used to help guide further evaluation (e.g., muscle biopsy, genetic testing); less commonly, they can make a definitive…

The majority of electrodiagnostic (EDX) studies are performed on outpatients, even in those electromyography (EMG) laboratories that are physically located within a hospital. However, an increasing number of EDX studies are done on patients in the intensive care unit (ICU). In the ICU setting, the patients typically are profoundly ill, often with several serious overlapping medical problems. Most are intubated and receiving mechanical ventilation, which prevents…

The myotonic muscle disorders compose a group of disorders characterized by muscle stiffness, pain, and sometimes weakness, which may be intermittent or constant. The primary periodic paralyses are rare inherited disorders associated with attacks of muscle paralysis. Depending on the specific disorder, attacks may last minutes, hours, or days, and some are associated with fixed weakness. The myotonic disorders and periodic paralyses are grouped together as…

In the evaluation of patients with suspected myopathy, molecular genetics has supplanted the need for electrodiagnostic (EDX) studies or muscle biopsy in many patients with inherited conditions. Moreover, in patients with suspected myopathy and no evidence of an inherited condition, a muscle biopsy ultimately will be required for definitive diagnosis, regardless of the findings on EDX studies. Despite these facts, EDX studies, especially the needle electromyography…

Disorders affecting the neuromuscular junction (NMJ) are among the most interesting and rewarding seen in the electromyography (EMG) laboratory. These disorders are generally pure motor syndromes that usually preferentially affect proximal, bulbar, or extraocular muscles. They are confused occasionally with myopathies. With knowledge of normal NMJ physiology (see Chapter 6 ), most of the abnormalities affecting the NMJ can be differentiated using a combination of nerve…

Sciatic neuropathies are uncommon in the electromyography (EMG) laboratory. When they occur, patients often present in a manner similar to that of peroneal neuropathy. Indeed, a foot drop from an early sciatic neuropathy may be difficult or impossible to distinguish clinically from a foot drop from peroneal neuropathy at the fibular neck . It often falls to the electromyographer to make this differentiation. Demonstration of a…

The anterior rami of the L1–S3 roots come together to form the lumbosacral plexus, from which all major lower extremity nerves are derived. Disorders of the lumbosacral plexus are distinctly uncommon, but when they occur, they typically present with a combination of pain, sensory loss, and weakness in the leg, in a manner similar to diseases of the nerve roots. Different patterns of clinical findings may…

Electromyographers are occasionally called on to evaluate the proximal nerves in the shoulder and arm. Isolated lesions of these nerves, including the suprascapular, axillary, musculocutaneous, long thoracic, and spinal accessory, are far less frequent than the common entrapment and compressive neuropathies of the median, ulnar, and radial nerves. The electrophysiologic evaluation of proximal neuropathies in the shoulder and arm relies principally on needle electromyography (EMG). Nerve…

The brachial plexus is a complicated anatomic structure formed by the ventral rami of the lower cervical and upper thoracic nerve roots. Different fascicles from those roots intermix widely within the plexus to ultimately form all the nerves of the upper extremity ( Fig. 33.1 ). In cases of suspected brachial plexopathy, nerve conduction studies and electromyography (EMG) often are used to localize the lesion accurately…

Radiculopathy is one of the most common diagnoses referred to any electromyography (EMG) laboratory. Even with the widespread use of magnetic resonance imaging, EMG continues to play an important role in the evaluation of radiculopathy. Although imaging studies usually are diagnostic in the more common radiculopathies caused by structural lesions, they are often unrevealing in radiculopathy caused by infection, infiltration, demyelination, or infarction. Whereas imaging studies…

There are a heterogeneous group of motor neuron disorders that are rare but nonetheless important to recognize because they often mimic the presentation of amyotrophic lateral sclerosis (ALS). These often are referred to as atypical motor neuron disorders . They include several infectious, inflammatory (presumably autoimmune or paraneoplastic), traumatic, and structural etiologies. Although many of the atypical motor neuron disorders share some features with ALS, they…

Electrodiagnostic (EDX) studies play a central role in the evaluation of patients with amyotrophic lateral sclerosis (ALS), the most common of all motor neuron disorders. Although described earlier by others, the French neurologist Jean-Martin Charcot is credited as naming the disorder amyotrophic lateral sclerosis in 1869. The name is derived from the Greek amyotrophic , which means “no nourishment to the muscle”; lateral , which refers…

Nerve conduction studies (NCSs) and electromyography (EMG) play key roles in the evaluation of patients with suspected polyneuropathy. Although polyneuropathy has hundreds of potential causes, they can be grouped into several large categories ( Fig. 29.1 ). The first step in the evaluation of a patient with polyneuropathy is to reduce the differential diagnosis to a smaller, more manageable number of possibilities. This usually can be…

Although nerve conduction and electromyography (EMG) studies are used most often to evaluate peripheral nerve and muscle disorders, they can also be used to evaluate lesions of the cranial nerves. Outside of the brainstem, the cranial nerves, other than cranial nerves I (olfactory) and II (optic), are essentially the same as peripheral nerves, carrying motor, sensory, and autonomic fibers. Mononeuropathies affecting cranial nerves VII (facial) and…

Patients with pain and numbness in the foot often are referred to the electromyography (EMG) laboratory for evaluation of possible tarsal tunnel syndrome (TTS). TTS results from entrapment of the distal tibial nerve under the flexor retinaculum at the medial ankle. Superficially, it might seem that tibial nerve entrapment under the flexor retinaculum at the ankle would be analogous to median nerve entrapment under the flexor…

Isolated lesions of the femoral nerve are uncommon in the electromyography (EMG) laboratory. More common are lesions of the lumbar plexus or L2–L4 nerve roots, which may present with symptoms and signs similar to femoral neuropathy. Especially in milder cases, differentiating among these three types of lesions may be quite difficult. The EMG serves two major roles in suspected lesions of the femoral nerve: first, to…

Peroneal neuropathy is one of the most common mononeuropathies in the lower extremity. Most often, peroneal neuropathy occurs at the fibular neck, where the nerve is quite superficial and vulnerable to injury. Patients usually present with a foot drop and sensory disturbance over the lateral calf and dorsum of the foot. However, patients with sciatic neuropathy, lumbosacral plexopathy, or L5 radiculopathy may present with a similar…