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A 42-year-old man used an electrical sander without protective gloves for 8 hours while cleaning rust from a fence (figure, A). Subsequently, he noted left thumb abduction weakness with …

Repetitive nerve stimulation and exercise testing are useful in the evaluation of patients with suspected disorders of the NMJ and muscle membrane excitability when performed with close attention to technical factors. They can be very helpful in the diagnosis of myasthenia gravis. Lambert-Eaton myasthenic syndrome, and botulism, as well as rare disorders of skeletal muscle membrane excitability, including paramyotonia congenita, myotonia congenita, myotonic dystrophy, and the periodic paralyses.

Electrodiagnostic procedures are routinely performed in patients with a variety of neuromuscular disorders. These studies are generally well tolerated and rarely thought to be associated with any significant side effects. However, needle electromyography is an invasive procedure and under certain situations has the potential to be associated with iatrogenic complications, including bleeding, infection, nerve injury, pneumothorax, and other local trauma. Similar complications are possible if needles are used for either stimulating or recording. In addition, like all other electrical devices and monitoring equipment connected to patients, electrodiagnostic testing carries the risk of stray leakage currents that under certain circumstances can result in electrical injury, especially in patients in the intensive care setting. Similarly, certain precautions are required during nerve conduction studies (NCS) in patients with pacemakers and other similar cardiac devices. In this review, we address the known and theoretical complications of NCS and needle electrode examination, and the possible methods to avoid such hazards.

The neuromuscular junction (NMJ) forms an electrochemical link transmitting the nerve action potential to muscle. A variety of disorders are known to impair the NMJ at the presynaptic or postsynaptic membrane. Among these disorders, myasthenia gravis (MG) is the most common, with an incidence of 2 to 10 cases in 100,000 people per year. Over the last 30 years, the autoimmune pathophysiology of MG has been well elucidated with the recognition of antibodies directed against the nicotinic acetylcholine receptor. Because this disorder is treatable and potentially curable, prompt recognition, especially early in the clinical course, is important. Mortality and morbidity, once not unusual in patients with MG, have been dramatically reduced in the modem era with early diagnosis and the use of immunosuppression, plasma exchange, and thymectomy.

The term electromyography (EMG) is commonly used inclusively to refer to electrodiagnostic testing, which involves nerve conduction studies in addition to the needle electrode examination of muscle. These studies are used primarily in evaluating the peripheral nervous system, including both motor and sensory nerves as well as muscle and neuromuscular junction. When correlated with the clinical examination, they are a powerful tool for localizing and determining the extent, severity, approximate time course, and pathophysiology of a lesion. The importance of clinical correlation for planning the appropriate study and interpreting the results cannot be overemphasized. Thus, every electrophysiologic evaluation should be preceded by an appropriately tailored history and neurologic examination, and the results of the study should be viewed in light of the clinical picture.

The needle electromyographic (EMG) examination is a challenging component of the electrophysiologic study. Knowledge of anatomy and physiology, sound EMG technique, and good patient rapport are required. Every muscle sampled by needle EMG is assessed for insertional activity, spontaneous activity, and voluntary motor-unit action potentials. Key pieces of information obtained from the needle EMG examination include the localization of the disorder, its chronicity, severity, and whether or not the underlying pathophysiology is neuropathic, myopathic, or associated with a neuromuscular junction disorder.

Patients with severe carpal tunnel syndrome (CTS) may occasionally have absent median motor and sensory responses; in these cases, it is not possible to accurately localize the median mononeuropathy to the wrist using standard electrodiagnostic tests. We prospectively investigated the use of comparing the median motor latency to the second lumbrical and the ulnar motor latency to the interossei muscles in 28 patient hands with severe CTS and absent median motor and sensory responses. We found a prolonged latency difference in 92.8%. Along with its use in mild CTS, study of the lumbrical-interossei latency difference is helpful in patients with severe CTS with absent median motor and sensory responses.

Precise electrophysiologic localization of ulnar neuropathy at the wrist(UNW) is often problematic. In the last year, we evaluated only two patients who presented clinically with UNW. Routine electrophysiologic techniques were nondiagnostic for UNW. In contrast, short-segment incremental studies (SSIS) across the wrist demonstrated conduction block and segmental slowing of nerve conduction across the wrist in both patients. We conclude that SSIS is a valuable tool for diagnosis, precise localization, and prognosis of UNW.

Isolated mononeuropathies often occur from compression and trauma but may also occur as the first manifestation of more serious underlying inflammatory disorders, which present in a mononeuropathy multiplex pattern. Differentiating these possibilities is essential to help guide further evaluation and treatment and assess prognosis. If a mononeuropathy follows an unrecognized episode of compression, it may be difficult to determine the etiology. However, an isolated mononeuropathy of certain nerves, especially the superficial radial sensory nerve, should always suggest the possibility of prior external compression. A 36-year-old neurologist, attending the annual American Academy of Neurology meeting, developed marked loss of sensation over the right lateral wrist extending into the thumb. This was noted immediately after a 30-minute seated conversation with a salesman in the exhibition hall. There was no pain, weakness, or difficulty with corrdination. Family history was negative for neurologic disease. On examination, there was a well-defined strip of anesthesia extending from the lateral wrist into the thumb up to the level of the nail bed (Figure 1). Sensation over the thenar …

We report a man with a slowly progressive bulbar palsy 14 years after radiation therapy for nasopharyngeal carcinoma.Electromyography demonstrated prominent myokymic and neuromyotonic discharges in muscles innervated by the lower cranial nerves. Late effects of radiation therapy can occur in the cranial nerve musculature that are similar to well-recognized syndromes affecting the brachial plexus and spinal cord.NEUROLOGY 1996;46: 1604-1606

Vertebrate sensory and motor axons vary in their responses to submaximal stimuli as a function of time since prior activation. When two equal but submaximal stimuli are presented in pairs, the response to the second stimulus may be greater or less than the response to the first stimulus, depending on the interstimulus interval (ISI). We studied both the supernormal period (ISI between 6 and 25 msec) and the subnormal period (ISI between 25 and 100 msec) under conditions where only single motor axons were stimulated. Twenty single motor units from eight normal subjects were studied. The behavior of single units was very similar to that observed in compound motor action potentials, with the supernormal period lasting approximately 20 msec, followed by a subnormal period lasting at least 80 msec. Surprisingly, a supernormal period could be evoked by a stimulus that did not produce a response in the motor unit being studied; however, the presence of subnormality was dependent on an action potential being generated in response to the first stimulus. Based on these results, we conclude that the supernormal period does not require the opening of voltage-dependent ion channels, in contrast to the later occurring subnormal period.

Article abstract-We report a woman with a chronic inflammatory myopathy who developed muscle stiffness and dystonic postures of both upper extremities. Electromyography demonstrated that involuntary complex repetitive discharges of muscle caused the posture. Rare cases of dystonic posturing may be of peripheral, and not central nervous system, origin.NEUROLOGY 1996;46: 257-258

Electrodiagnosis of carpal tunnel syndrome (CTS) often depends on the demonstration of focal slowing of median sensory fibers across the wrist. We compared the relative sensitivity of the four median innervated digits in demonstrating focal slowing in patients with CTS. Antidromic sensory studies of digits 1, 2, 3, and 4 were performed on 30 control subjects to develop normative data. Fifty-nine consecutive patients with CTS were then studied to determine the sensitivity of focal slowing of each median innervated digit. In the 26 CTS patients with a normal distal motor latency (DML) to abductor pollicis brevis, digit 1 was abnormal in 81%, digit 2 in 42%, digit 3 in 54%, and digit 4 in 38%. In the 33 CTS patients with a prolonged DML, digit 1 was abnormal in 94%, digit 2 in 88%, digit 3 in 91%, and digit 4 in 88%. We conclude that in milder cases of CTS with a normal DML, digit 1 is the most sensitive in identifying focal slowing of sensory conduction across the wrist. However, in patients with a prolonged DML, the sensitivity of sensory conduction is not significantly different among the four digits. © John Wiley & Sons, Inc.

The relative sensitivities of sensory, mixed nerve, and motor conduction studies in assessing ulnar neuropathy at the elbow have not yet been established. Using surface electrodes, we performed conduction studies across the elbow segment in 43 patients with symptoms referable to the ulnar nerve and 40 control subjects. Segmental slowing of motor conduction localized the lesion to the elbow in 14 of 21 patients (67%) with clear evidence of ulnar neuropathy on physical examination but only in 2 of 22 (9%) with subtle or no physical examination abnormalities. The diagnostic yield was increased by the finding of segmental slowing of sensory or mixed nerve conduction across the elbow to 86% and 68%, respectively, for each of the groups. We conclude that surface-recorded sensory and mixed nerve conduction studies appear to be more sensitive than motor studies in the electrodiagnosis of ulnar neuropathy at the elbow and are especially valuable in patients with subtle clinical involvement.

We report a woman with Guillain-Barre syndrome who developed a flexion posture of the right arm and hand resembling upper motor neuron dysfunction. EMG demonstrated that involuntary peripherally generated continuous motor unit discharges caused the posture.

The syndrome of neuromyotonia produces muscle stiffness, cramps, and frequently, excessive sweating. Most cases are idiopathic, but some are associated with neoplasms, especially immune cell cancers. Voltage-gated potassium channels may be the target of an autoantibody attack in idiopathic generalized neuromyotonia (Isaacs' syndrome). The cases associated with neoplasms may also have an autoimmune etiology. We report the first case of neuromyotonia as the presenting feature of Hodgkin's lymphoma and propose a paraneoplastic mechanism that would link the purported autoimmune etiology in Isaacs' syndrome with the cancer-associated cases.

A 23-year-old woman presented with 3 days of headache followed by complex partial seizures. Stereotactic aspiration of a large right temporal mass revealed purulent material with Gram-positive cocci …

Excerpt Any peripheral nerve is potentially vulnerable to needle-induced injury during routine procedures such as phlebotomy, intravenous line placement, joint aspiration, or intramuscular injectio...