Biomedical subjects
Publications and source records attributed to Asa J Wilbourn.
The EDX examination can be of considerable use to the clinician in the evaluation of focal peripheral nerve injuries. It can confirm the presence ofsuch lesions and help determine their location, severity, and prognosis. The major reason why it is capable of doing so is because it discloses the pathophysiology of focal neuropathies, at least in regard to large myelinated nerve fiber damage.
The authors present a retrospective study of 52 patients with main trunk tibial neuropathy. They found trauma and ischemia to be the most frequent causes, followed by tumors. These etiologic groups are underrepresented in the literature. Electrodiagnostic examination was helpful for localizing the lesion as well as for excluding S1 radiculopathies, with which tibial neuropathies can be confused clinically.
There are many conflicting theories regarding the mechanism and prognosis of acute foot drop during labor. We report seven women who had arrested labor and foot drop. Six had short stature and one had a large newborn. All had weakness of ankle dorsiflexion, eversion, and inversion, and sensory loss in the L-5 dermatome. Superficial peroneal sensory nerve action potentials (SNAPs) were small or absent in six patients, and the sural SNAP was attenuated in one. Peroneal compound muscle action potential (CMAP) amplitude (recording from extensor digitorum brevis) was low in five, whereas the tibial CMAP was normal in all patients. Peroneal CMAP amplitude (recording from the tibialis anterior) was normal in three and small in three. Needle electromyography revealed decreased recruitment and fibrillation potentials in L-5-innervated muscles, mostly below the knee. We conclude that intrapartum foot drop occurs mostly in short women and is caused by lumbosacral trunk compression by the fetal head at the pelvic brim. The primary pathology is predominantly demyelination and recovery is complete in up to 5 months.
Nerve conduction studies are essential components of the electrodiagnostic study. Several components might be analyzed and are diagnostically important. These include amplitude, duration, area, latency, and conduction velocity. Nerve lesions cause axon loss or demyelination, and in nerve conduction studies, have distinctive patterns. An important function of the electrodiagnostic examination, including nerve conduction studies and needle electromyography examinations, is to localize nerve lesions as accurately as possible.
Of the four major PNS plexuses, disorders of the brachial plexus are encountered far more frequently than those of the others. The EDX examination is probably the best procedure available by which to evaluate brachial plexus lesions. It provides localizing, pathologic, pathophysiologic, severity, and prognostic information. By localizing the lesion and identifying the underlying pathophysiology, it often predicts the underlying etiologic process; for example, (1) major T1 APR involvement with true neurogenic thoracic outlet syndrome; (2) C8 APR involvement with postmedian sternotomy brachial plexopathies; (3) supraclavicular demyelinating conduction block with classic postoperative paralysis (often confined to the upper plexus); (4) widespread infraclavicular demyelinating conduction blocks with radiation plexopathy; (5) severe progressive axon loss with neoplastic processes; (6) motor NCS abnormalities exceeding sensory NCS abnormalities for the same peripheral nervous system segment with intraspinal canal lesions (e.g., avulsions); (7) demyelinating conduction block with sparing of the pertinent sensory NCS study with multifocal motor neuropathy; and (8) lack of EDX abnormalities with hysteria, conversion reactions, and malingering, as well as with disputed neurogenic thoracic outlet syndrome. In addition, incorrect clinical considerations may be excluded (e.g., when abnormal SNAPs are identified, an isolated radiculopathy is excluded). Among the various EDX study components, the sensory NCS are the most useful for brachial plexus element localization. One drawback of the sensory NCS for localization occurs in the setting of concomitant carpal tunnel syndrome; the latter negates the utility of the median sensory NCS for brachial plexus localization. The motor NCS and NEE often overcome this drawback and, regardless of sensory NCS findings, are always performed.
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