Asa J. Wilbourn

AAEM Minimonograph 32: The electrodiagnostic examination in patients with radiculopathies

The anatomy and pathophysiology of radiculopathies are reviewed, and the electrodiagnostic approaches used in evaluating patients with suspected root lesions are discussed. Such electrophysiologic procedures include motor and sensory nerve conduction studies, late‐response studies, somatosensory and motor evoked potentials, nerve root stimulation, and needle electromyography. The value and limitations of these different procedures are considered. At the present time, needle electromyography is the single most useful approach. The findings in patients with radiculopathies at different levels are summarized. Muscle Nerve 21: 1612–1631, 1998

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.

Thoracic outlet syndromes.

The term thoracic outlet syndromes, is a group designation for several distinct disorders (one of questionable validity) involving various components of the brachial plexus, the blood vessels, or both, at various points between the base of the neck and the axilla. Four of the five subgroups (true neurologic TOS, arterial vascular TOS, venous vascular TOS, and traumatic neurovascular TOS) are universally recognized to be rare lesions, with characteristic clinical and laboratory presentations; and none is particularly controversial. In contrast, disputed neurologic TOS is highly controversial. This article limits discussion to the three subgroups of TOS in which neurologic symptoms are caused, or reputedly are caused, by compromise of the brachial plexus fibers.

Ischemic rnonornelic neuropathy

Ischemic monomelic neuropathy (IMN) is an infrequently recognized type of ischemic neuropathy produced by the shunting of blood away from, or the acute noncompressive occlusion of, a major proximal limb artery. IMN consists of multiple axonal-loss mononeuropathies that develop acutely and simultaneously in the distal portion of a limb. We found stereotyped clinical and EMG features in 14 patients. In six the IMN was thromboembolic in nature, whereas in eight it was due to various vascular surgical procedures. Our experience with IMN suggests that distal axonal infarction can occur without significant muscle necrosis, supporting the hypothesis that in humans the distal nerve fibers are more vulnerable than muscle to acute noncompressive limb ischemia.

Cervical radiculopathies: Comparison of surgical and EMG localization of single-root lesions

To identify the various electrodiagnostic (EDX) patterns of C-5, C-6, C-7, and C-8 cervical radiculopathy, we compared 50 cases of surgically proven solitary-root lesions with their preoperative EDX patterns. We excluded patients with polyradiculopathy, myelopathy, and previous surgery. We classified EDX studies as abnormal only by the needle electrode examination, and only by the demonstration of fibrillation potentials (either the positive sharp wave or the biphasic spike form). Seven patients (14%) had C-5 radiculopathy, nine (18%) had C-6, 28 (56%) C-7, and six (12%) C-8. With C-5, C-7, and C-8 radiculopathies, changes were relatively stereotyped, with involvement of the spinati, deltoid, biceps, and brachioradialis with C-5; the pronator teres, flexor carpi radialis, triceps, and anconeus with C-7; and the first dorsal interosseous, abductor digiti minimi, abductor pollicis brevis, flexor pollicis longus, and extensor indicis proprius with C-8. The root lesion with the most variable presentation was C-6--in half the patients, the findings were similar to C-5 radiculopathies, except that the pronator teres tended to be involved, whereas in the other half, the findings were identical to those with C-7 radiculopathies. NEUROLOGY 1996;46: 1022-1025

Brachial plexopathy: recurrent cancer or radiation

We reviewed clinical and electrodiagnostic features of 16 patients with neoplastic brachial plexopathy (NBP) and 17 patients with radiation-induced plexopathy (RBP). The groups were similar in symptom-free interval after cancer diagnosis and location of the plexus lesions. NBP patients had pain and Horners syndrome; RBP patients had paresthesias, but rarely Horners. NBP patients presented earlier after symptom onset and had a shorter course. RBP patients more frequently had abnormal sensory and normal motor nerve conduction studies and characteristically had fasciculations or myokymia on EMG.

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.

IATROGENIC NERVE INJURIES

Iatrogenic nerve injuries are an undesired byproduct of the practice of medicine and have been so since antiquity. The majority of such injuries occur perioperatively, and are, therefore, attributed to surgeons and anesthesiologists. Nonetheless, the members of almost every clinical specialty are at risk to some degree. Iatrogenic nerve injuries can affect almost any portion of the peripheral nervous system, and can result from many different causes. This article reviews many of the more common iatrogenic nerve lesions.

Amyotrophic lateral sclerosis Effects of acute intravenous and chronic subcutaneous administration of thyrotropin‐releasing hormone in controlled trials

We performed double-blind crossover trials to assess the effects of thyrotropin-releasing hormone (TRH) on amyotrophic lateral sclerosis patients. For acute intravenous trials, 500 mg TRH or placebo with norepinephrine was given at 1-week intervals (16 patients). CSF TRH concentration increased, and clinical side effects appeared with TRH. For chronic studies, 25 mg TRH and a saline placebo were given subcutaneously every day for 3 months (25 patients). CSF TRH level increased 29-fold after a single TRH injection, and mild transient side effects occurred. Vital signs, respiratory function, semiquantitative and quantitative neurologic function, muscle strength by manual and dynamometer testing, and EMG were studied. With daily TRH, 10 patients noted subjective improvement without objective evidence, and 10 patients complained of worsening of the disease with objective decline after TRH was stopped. Statistical analysis, however, showed no beneficial effects from either acute or chronic TRH trials.

Cervical radiculopathy and coexisting distal entrapment neuropathies: Double-crush syndromes?

The double-crush hypothesis (DCH) proposes that a proximal lesion along an axon predisposes it to injury at a more distal site along its course through impaired axoplasmic flow. Although this hypothesis has been accepted, it has anatomic and pathophysiologic restrictions that limit its application as an explanation for coexisting cervical root lesions (CRLs) and carpal tunnel syndrome (CTS) or ulnar neuropathy at the elbow (UN-E). We retrospectively surveyed all electrodiagnostic (EDX) reports of coexisting CTS or UN-E and CRL for anatomic correlation, if any, between the proximal root lesion and the distal entrapment neuropathy. In the period between January 1982 and August 1995 there were 12,736 limbs with CTS or UN-E. In 435 of these limbs(3.4%) there was a coexisting CRL, but only 98 (0.8%) had an association that was anatomically appropriate. Moreover, only 69 (0.5%) of the 98 cases demonstrated axon loss at the distal lesion site on EDX examination. Therefore, cumulatively, only 69 of our 12,736 cases of CTS and UN-E satisfied the pathophysiologic and one of the anatomic requirements of the DCH. Our data thus suggest that a CRL can seldom serve as the proximal lesion with these entrapment neuropathies in the DCH.