In some nerves, such as the ulnar motor nerve, this pattern can also mimic an anomalous innervation. Next, if co-stimulation occurs distally but not proximally, there may be the mistaken impression of a conduction block proximally (see Fig. First, a low-amplitude potential due to axonal loss may reach the normal range if an adjacent nerve is co-stimulated. Inadvertent co-stimulation of adjacent nerves can create a host of problems, even in routine nerve conduction studies ( Figs. In this situation, the effects of co-stimulation can only be eliminated by the use of collision studies (see Chapter 33). In the upper extremity, stimulation at Erb’s point or at the C8–T1 nerve roots always results in co-stimulation of both the ulnar and median nerves. In the lower extremity, co-stimulation of the peroneal and tibial nerves may occur at the knee.Ĭo-stimulation of adjacent nerves is unavoidable when stimulating very proximal nerves and nerve roots. Co-stimulation occurs most commonly in motor studies of the upper extremity when the median and ulnar nerves are stimulated at the wrist, elbow, and axilla. As nearby nerves are excited, spuriously large amplitude potentials may result, caused by the inadvertent co-recording of additional nerve or muscle potentials beyond the potential of interest. As the stimulus current is increased, the current may spread to excite nearby nerves. In pathologic situations, however, nerves often require higher currents to achieve supramaximal stimulation. In individuals with normal nerves and normal stimulation thresholds, co-stimulation is not a common problem. Preston MD, in Electromyography and Neuromuscular Disorders, 2021 Co-Stimulation of Adjacent NervesĪlthough it is imperative to ensure that supramaximal stimulation has been achieved at all stimulation sites, preventing co-stimulation of adjacent nerves is equally important.
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