3 - Basic Nerve Conduction Studies

Abstract

Every electrodiagnostic study begins with nerve conduction studies (NCSs). The needle electromyography (EMG) examination is performed after the NCSs are completed because the findings on the NCSs are used in the planning and interpretation of the needle EMG examination that follows. Peripheral nerves usually can be easily stimulated and brought to action potential with a brief electrical pulse applied to the overlying skin. Techniques have been described for studying most peripheral nerves. In the upper extremity, the median, ulnar, and radial nerves are the most easily studied; in the lower extremity, the peroneal, tibial, and sural nerves are the most easily studied. The nerves selected for study depend on the patient’s symptoms and signs and the differential diagnosis. Motor, sensory, or mixed nerve studies can be performed by stimulating the nerve and placing the recording electrodes over a distal muscle, a cutaneous sensory nerve, or the entire mixed nerve, respectively. Information from NCSs includes latency, amplitude, duration, and conduction velocity. The key findings from motor, sensory, and mixed nerve studies often complement one another and yield different types of information based on distinct patterns of abnormalities, depending on the underlying pathology.