Lesion distribution among 281 patients with sporadic neuralgic amyotrophy.

INTRODUCTION: The muscles commonly affected by neuralgic amyotrophy (NA) are well known, but the location of the responsible lesions is less clear (plexus versus extraplexus). METHODS: We report the lesion locations in 281 NA patients as determined by extensive electrodiagnostic (EDX) testing. RESULTS: Our 281 patients had 322 bouts of NA, 57 of which were bilateral, for a total of 379 assessable events. A single nerve was involved in 174 (46%), and 205 (54%) were multifocal. EDX testing identified 703 individual lesions: 699 neuropathies and 4 supraclavicular radiculoplexus lesions. CONCLUSIONS: The frequency of nerve involvement reflects the motor predilection of NA. Involvement of pure motor nerves exceeded that of predominantly motor nerves, both of which far exceeded involvement of more evenly mixed sensorimotor nerves. Cutaneous sensory nerves were least commonly involved. Because of the common C5-C6 innervation, NA often mimics an upper plexus lesion. Extraplexus nerve involvement far exceeded plexus involvement. Distal motor branch involvement explains the severe single-muscle wasting and weakness often observed. Muscle Nerve 55: 858-861, 2017.

Electrodiagnostic features of true neurogenic thoracic outlet syndrome.

INTRODUCTION: We report the electrodiagnostic (EDX) features of 32 patients with surgically verified true neurogenic thoracic outlet syndrome (TN-TOS). METHODS: Retrospective record review. RESULTS: We found uniform EDX evidence of a chronic axon loss process that affected the lower portion of the brachial plexus and disproportionately involved the T1 more than the C8 sensory and motor fibers. Because of this relationship, the medial antebrachial cutaneous sensory nerve (T1) and median motor (T1 > C8) study combination was abnormal in 89%, whereas response combinations that primarily assessed the C8 fibers were less frequently affected. CONCLUSIONS: The characteristic EDX features of TN-TOS are T1 > C8 nerve fiber involvement. A comprehensive EDX examination of the lower plexus with contralateral comparison studies is imperative to diagnose this disorder accurately.

Pitfalls in the electrodiagnostic studies of sacral plexopathies.

This retrospective review characterizes the electrodiagnostic (EDX) features and etiologies of sacral plexopathies (SPs) and discusses difficulties in their identification. The EDX findings of 171 clinically suspected SPs were reviewed using the following criteria: reduced/absent sensory nerve action potentials (SNAPs) of the sural or superficial peroneal nerve, denervation of plexus-innervated muscles, and the absence of paraspinal denervation. Sixty cases localized unequivocally to the sacral plexus. The majority were cancer-related, followed by traumatic, idiopathic, and iatrogenic causes. Final diagnoses in the remaining 111 cases were indeterminate. Lesions localized to either the plexus or L4-5, S1 roots in 52 cases, the plexus or sciatic nerve in 32 cases, and were equally compatible with an SP, sciatic neuropathy, or radiculopathy in 27 cases. Findings in the EDX evaluation of SPs are often complex and difficult to localize to a specific site due to multiple complicating factors. Frequently, SPs cannot be diagnosed definitively by EDX assessment alone.

Plexopathies.

The neural plexuses are intricate networks of nerve fibers interposed between the spinal cord or anterior primary rami proximally and the most proximal portions of peripheral nerves distally. If the lumbar and sacral plexuses are considered as a single entity, then they constitute the largest peripheral nervous system structure. Each of the plexuses varies substantially from the others in its overall vulnerability to injury, the specific types of trauma or disease that most often affects it, and the ease with which it is assessed by the two laboratory diagnostic procedures in current use for doing so: neuroimaging studies and electrodiagnostic examinations.

Phrenic neuropathy due to neuralgic amyotrophy.

The authors reviewed the medical records of 33 patients diagnosed with idiopathic phrenic neuropathy and found that 17 patients had clinical features of neuralgic amyotrophy. They concluded that a careful clinical and electrodiagnostic evaluation may implicate neuralgic amyotrophy as a causative disease in patients with apparently isolated phrenic neuropathy.

Infraclavicular brachial plexus injury following axillary regional block.

Infraclavicular brachial plexopathy is a potential complication of axillary regional block. We retrospectively reviewed 13 such injuries and found the median nerve most often affected, followed by combined median and ulnar neuropathies, and then by various combinations involving the median, ulnar, radial, and musculocutaneous nerves. All were axon-loss in type and most were severe in degree electrophysiologically. The clinical and electrodiagnostic features of these injuries are strikingly similar to those sustained after axillary arteriography, which has been associated with the medial brachial fascial compartment (MBFC) syndrome. This syndrome is characterized by the evolution of neurologic deficits and pain following hematoma formation within a compartment of the upper arm. Thus, we believe that this mechanism underlies most nerve injuries that result from axillary angiography or axillary regional block. This has important treatment implications, as timely surgical intervention may lead to improved outcome.

The medial brachial fascial compartment syndrome following axillary arteriography.

OBJECTIVE: To review clinical and electrodiagnostic features of the medial brachial fascial compartment syndrome, a complication of percutaneous axillary vessel puncture. METHODS: The authors reviewed electrodiagnostic examinations over a 20-year period. RESULTS: This syndrome presents with weakness, pain, and numbness during or following the percutaneous procedure. Injury is characterized by axon loss and involves terminal nerves of the infraclavicular brachial plexus-most often the median nerve alone, followed by combinations of the median, ulnar, radial, and musculocutaneous nerves. CONCLUSIONS: Early recognition of the medial brachial fascial compartment syndrome may lead to prompt surgical intervention, which, in turn, may prevent permanent nerve injury. Late diagnosis generally results in poor outcome and often results from delayed symptom onset and lack of overt compartment syndrome signs.

The electrodiagnostic examination with peripheral nerve injuries.

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.

Main trunk tibial neuropathies.

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.

Intrapartum maternal lumbosacral plexopathy.

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. Types, components, abnormalities, and value in localization.

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.

Electrodiagnostic approach to the patient with suspected brachial plexopathy.

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.