EMG findings early after peripheral nerve lesions

Abstract

Introduction: Increased discharge rates of motor units in concentric needle electromyography (EMG) indicate a loss of motor units and thus a peripheral neurogenic lesion. In contrast, discharge rates of motor units tend to be decreased in lesions of the central nervous system. It is not known whether increased discharge rates can be found immediately after a peripheral nerve lesion or after some time. Methods: Concentric needle EMG and neurography were done in 6 patients within the first 2 days after a traumatic lesion of a peripheral nerve. Kind and severity of the lesion were further characterized in at least one follow-up visit. Results: The initial EMG studies took place from 3 to 48 hours after the trauma. Abnormally increased discharge rates of at least 20Hz were found in all affected muscles weaker than MRC 4. The discharge rates did not depend on the kind of the lesion, namely neurapraxia or axonotmesis. Conclusion: Measurement of discharge rates of motor units is useful immediately after a sudden muscular weakness is noted by a patient. It may help to differentiate between a central and a peripheral lesion, but cannot differentiate between neurapraxia or axonotmesis.