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INTRODUCTION

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The role of laboratory testing in the diagnosis of neuromuscular disease is described in the first chapter. Tests are ideally used to support a clinically established working diagnosis, not in a random search process. False-positive test results occur with some frequency, and can easily lead to unnecessary testing and interventions as well as potential harm if not measured against pensive clinical analysis.

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This chapter will focus on nonhistologic tests that are readily available to most clinicians and potentially useful to the neuromuscular physicians in their assessment of patients. In keeping with the philosophy of this text, emphasis will be placed on tests that have pragmatic application. The science behind the testing will be provided only to the extent necessary to understand the utility, performance, interpretation, and limitations of a test within a given clinical context. The following topics will be addressed:

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  • Electromyography (EMG) and nerve conduction studies (NCS), collectively known as electrodiagnosis (EDX)

  • Quantitative sensory testing (QST)

  • Autonomic nervous system testing (ANST)

  • Routine laboratory (blood) testing

  • DNA mutational analysis

  • Biochemical testing for inborn errors of metabolism

  • Serologic testing

  • Cerebrospinal fluid (CSF) analysis

  • Nerve and muscle imaging

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EMG AND NCS (EDX)

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BASIC PRINCIPLES

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Physician Skill and Knowledge
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Like all tests, EDX has limitations, as do the people who order, perform, and interpret them. The most satisfactory results occur when the requesting physician understands the tests' value and limitations, and posits specific questions to the electromyographer that the test is capable of answering. A satisfactory result is also dependent on an electromyographer who examines the patient, understands the differential diagnosis of the clinical problem, and tailors the electrodiagnostic examination to adequately explore those possibilities. In keeping with this philosophy, it is readily understandable that the nerves tested during NCS and the muscles selected for EMG, although often guided by algorithm, are frequently modified both on a case-by-case basis both prior to and during its performance.

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Temperature Considerations
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Attention to detail is important in EDX. One notable example is attention to limb temperature. As a general rule, hand temperatures of >33°C and foot temperatures of >31°C are desirable. Although warm water baths and heating lamps may be used, in our experience, reusable microwaveable heating pads applied to the limbs are the most effective technique for obtaining and maintaining this thermal environment.

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With cold limbs, amplitudes of both compound motor action potentials (CMAP) and sensory nerve action potentials (SNAP) are increased. Abnormally low CMAP and SNAP amplitudes could be potentially normalized. Conversely, conduction speeds are reduced, including slowing of conduction velocities and prolongation of distal, F wave, and H reflex latencies (Fig. 2-1). Repetitive stimulation techniques are also affected by limb temperature. Limb cooling diminishes the degree of the decremental response in patients with disorders of neuromuscular transmission (DNMT). Failure to maintain adequate ...

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