![]() NCS parameters include amplitude (µV for sensory, mV for motor), distal latency (DL, in msec) from the most distal point of stimulation, and conduction velocity (CV, in m/sec) calculated in nerve segments demarcated by the selected points of stimulation. Recording electrodes are placed for sensory NCS over the nerve, and for motor NCS mostly over compact, usually distal superficial muscles. NCS measure voltage potential differences between two electrodes, the first recording over a nerve or muscle at an informative site at some distance from the stimulation point, the second a “neutral” reference. The patient feels an instantaneous shock but usually not the wave of induced depolarization as it travels up and down the nerve itself. In sensory and motor NCS, a square-wave stimulus in milliamps (mA) is delivered, usually percutaneously, to test points along the nerve, causing it to depolarize. Both tests measure electrical potentials generated by nerves and muscles. ![]() NCS are generally more important in diagnosing nerve entrapments and injuries, but needle EMG is necessary to most studies for the complementary information it provides. The purpose of this chapter is to elucidate that indispensable conceptual framework. Patients are best served when referring clinicians and neurophysiologists communicate on the basis of mutually understood interpretative principles, including what NCS and EMG actually test, their limitations, and timing considerations crucial to meaningful conclusions. Is CTS or another entrapment present? How severe is it? What is the precise localization? Are there atypical features or concurrent disorders such as radiculopathy or polyneuropathy? Do the neurophysiologic findings explain the patient’s symptoms and signs, or are they at least consistent with them? Do they indicate additional or unsuspected diagnoses, or reveal a need for radiologic or other testing? Do the study design and results support the final interpretation logically and scientifically? Numerous textbooks, reviews, and courses are available with background information on neurophysiologic theory and techniques. This chapter develops a practical framework to enable referring clinicians and hand therapists to correlate clinical results and judge the quality of NCS and EMG reports.Ĭlinicians ordering studies seek pragmatic answers that will help their patients. The optimal neurophysiologist is a physician, fellowship-trained and board-certified in electrodiagnostic medicine, adept in sophisticated examination and neuromuscular pattern recognition, and flexible enough to consistently perform studies tailored to each patient’s circumstance. Neurophysiologists should provide prompt, understandable, “bottom line” answers that define PNS lesion and context in terms of the referral question and neurologic exam. Unlike clinical tests, such as Phalen’s sign, that focus on specific nerve entrapments such as carpal tunnel syndrome (CTS),, well-designed NCS and EMG provide not only objective, localizing, prognostically important data about the clinically suspected lesion but also indispensable PNS context about concurrent mononeuropathies, polyneuropathy, myopathy, and other neuromuscular disorders. NCS and EMG rank second in importance only to obtaining a careful history and performing a neurologic examination for accurate and localizing diagnosis of nerve entrapments and disorders of the peripheral nervous system (PNS). Optimal neurophysiologic consultation is a process that calls for excellent communication between neurophysiologist and referring clinician before and after the study, as well as between patient and neurophysiologist during the study. NCS are generally more important in diagnosing nerve entrapments and injuries, but needle EMG is necessary to most studies for the complementary information it provides.īoth NCS and EMG measure electrical potentials generated by nerves and muscles. NCS and EMG also provide peripheral nerve system context about concurrent mononeuropathies, polyneuropathy, myopathy, and other neuromuscular disorders. Nerve conduction studies (NCS) and electromyography (EMG) provide objective, localizing, prognostically important data about clinically suspected lesions.
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