Discharge rates in electromyography distinguish early between peripheral and central paresis

Abnormally increased discharge rates (DRs) of motor unit potentials on concentric needle electromyography (CNEMG) indicate a loss of motor units in peripheral neurogenic lesions. Methods: To determine when increased DRs occur during the course of a peripheral nerve lesion, we retrospectively analyzed CNEMG recordings of 19 patients with acute weakness of peripheral origin. Results: The initial CNEMG studies took place from 3.7 hours to 10 days after the onset of the lesion. Abnormally increased DRs (≥20/s) were found in all but 1 of the muscles in which MRC grade was <4. Peripheral neurogenic damage was confirmed in all patients thereafter. The DRs depended on neither the kind of lesion nor the time between onset and CNEMG examination. Conclusions: The measurement of DRs of motor unit potentials is helpful immediately after a sudden paresis of MRC grade 3 or worse to differentiate between a central and a peripheral lesion. Muscle Nerve 46: 596–598, 2012