Mark A. Ferrante

The characteristic electrodiagnostic features of Kennedy's disease

To define the electrodiagnostic (EDX) features of Kennedys disease, their distribution, their clinical correlation, and to determine whether they are unique to this disorder, we retrospectively evaluated the EDX and clinical features of 19 patients with Kennedys disease and found that: (1) the percentage with sensory nerve action potential abnormalities is high (95%); (2) compound muscle action potential abnormalities are less frequent (37%) and less pronounced; (3) the needle electrode examination is always abnormal (100%), revealing acute and chronic motor axon loss, with the latter predominating; (4) the clinical onset is heterogeneous for both the site of onset (bulbar, upper extremity, lower extremity, combination) and the symptomatology (sensory, motor, sensorimotor); (5) focal onsets were reported in the majority (79%); and (6) there is a strong correlation between the clinical onset (both site and symptomatology) and the maximal EDX abnormalities. Thus, the EDX features of Kennedys disease are consistent with a slowly progressive and very chronic degeneration of the anterior horn cells and dorsal root ganglia. Although the clinical onsets are heterogenous, the EDX features are homogenous and unique, consisting of a diffuse, very slowly progressive anterior horn cell disorder coupled with a sensory neuropathy/neuronopathy that mimics an acquired process.

Utility of electrodiagnostic testing in evaluating patients with lumbosacral radiculopathy: An evidence-based review.

This is an evidence‐based review of electrodiagnostic (EDX) testing of patients with suspected lumbosacral radiculopathy to determine its utility in diagnosis and prognosis. Literature searches were performed to identify articles applying EDX techniques to patients with suspected lumbosacral radiculopathy. From the 355 articles initially discovered, 119 articles describing nerve conduction studies, electromyography (EMG), or evoked potentials in adequate detail were reviewed further. Fifty‐three studies met inclusion criteria and were graded using predetermined criteria for classification of evidence for diagnostic studies. Two class II, 7 class III, and 34 class IV studies described the diagnostic use of EDX. One class II and three class III articles described H‐reflexes with acceptable statistical significance for use in the diagnosis and confirmation of suspected S1 lumbosacral radiculopathy. Two class II and two class III studies demonstrated a range of sensitivities for use of muscle paraspinal mapping. Two class II studies demonstrated the utility of peripheral myotomal limb electromyography in radiculopathies. Muscle Nerve 42:276–282, 2010

The thoracic outlet syndromes.

The term thoracic outlet syndrome (TOS) refers to a heterogeneous group of disorders, all of which have in common compression of one or more neurovascular elements at some point within the thoracic outlet. Of the five disorders comprising this group, four have all of the features expected of a syndrome—a recognized constellation of clinical features; an anatomic derangement accounting for these features; and a method of testing that identifies the anatomic derangement. Consequently, their recognition and management are relatively straightforward. Conversely, one of these five disorders (nonspecific TOS) lacks these correlations, which has generated considerable debate in the literature and caused some experts to doubt its existence altogether. The primary focus in this study is on the neurologic forms of TOS. However, for completeness and a better understanding of these neurologic manifestations, the vascular forms are also reviewed. Muscle Nerve 45: 780–795, 2012

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.

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. Muscle Nerve 49: 724–727, 2014

The Lesion Distribution among 281 Patients with Sporadic Neuralgic Amyotrophy

The muscles commonly affected by neuralgic amyotrophy (NA) are well known, but the location of the responsible lesions is less clear (plexus versus extraplexus).

Electrodiagnostic Assessment of the Brachial Plexus

The brachial plexus is one of the largest and most complex structures of the peripheral nervous system and, as such, cannot be studied by a single nerve conduction study (NCS) or muscle sampled by needle electrode examination (NEE). Typically, the screening sensory NCS is used and expanded to identify the region of involvement, the motor NCS is applied to determine the severity of the process, and the NEE is used to further characterize the lesion. Our approach to the electrodiagnostic assessment of the brachial plexus is the focus of this article; 3 electrodiagnostic cases with discussion follow this article.

The distribution of neuralgic amyotrophy lesions is overwhelmingly extraplexal: Editorial

Neuralgic amyotrophy is a disorder of the peripheral nervous system (PNS) that is associated with a wide range of clinical phenotypes. For this reason, roughly 2 dozen terms have been applied to it, some reflecting the muscle involved (serratus magnus palsy) and others reflecting the presumed lesion site (idiopathic brachial plexitis, idiopathic brachial neuritis). In 1948, Parsonage and Turner recognized that all of these entities represented the same disorder and introduced the term neuralgic amyotrophy to highlight its 2 quintessential features, severe pain and pronounced muscle wasting. In addition to these 2 features, an antecedent event (trigger) is often identified. In the presence of this unifying triad (antecedent event, severe pain, and pronounced muscle wasting), neuralgic amyotrophy is easily recognized. Regarding its localization, although most investigators initially considered neuralgic amyotrophy to be a brachial plexus disorder, many authors have since speculated that at least some of the time it behaves more like an extraplexal disorder. Others, on the basis of both clinical and electrodiagnostic (EDX) findings, have suggested that it rarely involves the brachial plexus and, instead, represents an extraplexal disorder of the forequarter region of the body that presents as either a mononeuropathy or a multiple mononeuropathy, depending on the number of individual nerves involved. We recently evaluated the lesion distribution among 281 patients with sporadic neuralgic amyotrophy. In that study, 699 of 703 lesions were extraplexal nerve lesions; only 4 involved the brachial plexus. The extraplexal lesions had a mononeuropathy (46%) or a multiple mononeuropathy (54%) distribution. Consistent with the belief that neuralgic amyotrophy has a predilection for motor axons, the incidence of nerve involvement in that study reflected the percentage of motor axons composing the nerve as follows: pure motor nerves (e.g., suprascapular, long thoracic, distal motor branch, anterior interosseous)>predominantly motor nerves (e.g., axillary, musculocutaneous)>>mixed nerves (e.g., median, ulnar, radial)>> cutaneous sensory nerves (e.g., lateral antebrachial cutaneous). As a result of this motor axon predilection, nerves innervating the shoulder girdle muscles are frequently involved. Whenever 2 or more such nerves are involved, an upper plexus localization is suggested. However, unlike upper plexopathies, in which nerve conduction study abnormalities are simultaneously present in both the lateral antebrachial cutaneous nerve and the median sensory nerve recording from the thumb 96% of the time, this pattern is unexpected with neuralgic amyotrophy; in our study of 281 patients, it was never observed. In addition to EDX studies, imaging studies are also frequently employed in the evaluation of neuralgic amyotrophy patients, not only to assess the brachial plexus but also to exclude mimicking entities. In this issue of Muscle & Nerve, Sneag et al., having used high-resolution MRI, report the MRI manifestations of neuralgic amyotrophy in 27 patients. Through a retrospective search of the imaging database of their institution, they identified 27 patients with clinically and electrodiagnostically confirmed neuralgic amyotrophy. The clinical and EDX findings in these patients indicated 38 extraplexal (nerve) lesions. None of the clinical or EDX assessments suggested brachial plexus involvement. Among these 38 nerve lesions, 37 were based on both clinical and EDX assessments and 1 was based on clinical assessment alone (this patient had presented with a suprascapular mononeuropathy, the classic triad of neuralgic amyotrophy, and did not undergo EDX assessment). Two radiologists independently assessed the brachial plexus MRI studies, which included the preterminal (e.g., suprascapular) and terminal (e.g., musculocutaneous) nerves of the brachial plexus whenever they were present within the field of view of the study. Correspondence to: M. A. Ferrante; e-mail: mafmd1@gmail.com

Nonvasculitic Ischemic Neuropathies

There are a number of disorders, other than vasculitis, in which nerve fibers sustain ischemic injury. This heterologous group is composed of entities caused by compromise of arterial blood flow in vessels of markedly various sizes. Moreover, with some of them, concomitant damage to structures other than neural tissue (e.g., muscle) is an integral component. Six of these disorders are reviewed in this chapter: (1) compartment syndromes, (2) ischemic monomelic neuropathy, (3) acute ischemic mononeuropathy/plexopathy (nerve damage due to embolism or stenosis), (4) chronic limb ischemia (atherosclerotic polyneuropathy), (5) frostbite, and (6) hand-arm vibration syndrome. This chapter discusses these disorders’ pathogenesis, causes, and treatment.