Introduction to the Needle Electrode Examination
Needle EMG remains an important part of the evaluation of the peripheral nervous system and can assist substantially in characterizing a variety of disease states. The needle electrode examination generally consists of three parts: evaluation of spontaneous activity, evaluation of motor unit potential morphology, and evaluation of motor unit potential recruitment. Abnormal spontaneous activity includes the commonly observed fibrillation potential and positive sharp wave and the less frequent myotonic, myokymic, neuromyotonic, and complex repetitive discharges. Neurogenic disease produces prolonged duration and increased amplitude of motor unit potentials with reduced recruitment, whereas myopathic disease generally produces low-amplitude, short-duration motor unit potentials, with normal or early recruitment. An understanding of the basic mechanisms of these disease changes can greatly aid in the interpretation of EMG data. Finally, the distribution of abnormalities across muscles can also aid in diagnosis, especially in the assessment of radiculopathy and plexopathies.
Key WordsFibrillation potential motor unit potential motor unit recruitment myotonic discharge needle electromyography positive sharp wave
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