Rubin, Devon I.

ABSTRACTIntroduction: G1 electrode placement at the distal wrist crease during the median orthodromic palmar nerve conduction study (NCS) could result in a false negative study if compression is more proximal. Methods: In this study we aimed to determine the effect of median G1 electrode placement on distal latencies and amplitudes. Methods Median orthodromic palmar NCS was performed with the G1 electrode at the wrist crease and 2 cm proximal, stimulating 8 cm distal to G1. The difference in the distal latencies and amplitudes between the 2 recording sites was calculated. Results: In 26 controls and 25 carpal tunnel syndrome (CTS) patients, the mean proximal–distal latency difference and percent amplitude decrease (distal vs. proximal) was −0.085 ms/53% (controls) and −0.072 ms/45% (CTS). Conclusion: Distal latency is not significantly affected by G1 placement in the median orthodromic palmar NCS, but the amplitudes are nearly twice as high when G1 is placed 2 cm proximal to the wrist crease. Muscle Nerve 53: 579–582, 2016

ABSTRACTIntroduction: Repetitive discharges may be recorded during nerve conduction studies (NCS) or during needle electromyography in a muscle at rest. Repetitive discharges that occur during voluntary activation and are time‐locked to voluntary motor unit potentials (MUP) have not been described. Methods: Retrospective review of motor unit potential induced repetitive discharges (MIRDs) identified in the EMG laboratory. Characteristics of each MIRD, patient demographics, other EMG findings in the same muscle, and electrophysiological diagnosis were analyzed. Results: MIRDs were observed in 15 patients. The morphology and number of spikes and duration of MIRDs varied. The discharges fired at rates of 50–200 Hz. All but 2 patients had EMG findings of a chronic neurogenic disorder. Conclusions: MIRDs are rare iterative discharges time‐locked to a voluntary MUP. The pathophysiology of MIRDs is unclear, but their presence may indicate a chronic neurogenic process. Muscle Nerve 48: 977–979, 2013

ABSTRACTIntroduction: The utility of F‐waves in assessing radiculopathies is debated. The aim of this study is to determine the frequency of abnormal minimum tibial F‐wave latencies compared to an F‐estimate and an absolute reference value in patients with electromyography (EMG) confirmed S1 radiculopathies. Methods: A retrospective review of F‐waves in patients with an EMG‐confirmed isolated S1 radiculopathy was performed. The minimum and mean latencies of 8 tibial F‐waves were compared with the calculated F‐estimate and to an absolute reference value, and the frequencies of abnormal responses were determined. Results: Of the 50 patients with an S1 radiculopathy, 4% had prolongation of the minimum reproducible F‐wave latency, and 8% had prolongation of the mean latency relative to the calculated F‐estimate. Conclusions: The minimum and mean F‐wave latencies are infrequently abnormal when compared with an estimated F‐wave latency in S1 radiculopathies and are insensitive in the assessment of S1 nerve root injury. Muscle Nerve 49: 809–813, 2014