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J Korean Assoc EMG Electrodiagn Med 2017;19(2):61-66.
Published online December 31, 2017.
Electrophysiologic Analysis of the Split Hand Phenomenon in Amyotrophic Lateral Sclerosis
Received: 29 August 2017   • Revised: 20 November 2017   • Accepted: 30 November 2017
Objective: We investigated the clinical and electrophysiological expressions of the thenar muscular atrophy in patients with amyotrophic lateral sclerosis (ALS) and evaluated whether the selective involvement of thenar muscles was caused by the split hand phenomenon or by overlapping peripheral neuropathies. Method: We retrospectively compared electrophysiologic data of 35 ALS patients to 50 age-matched healthy control subjects. We further compared electrophysiologic data of the ALS patients with peripheral neuropathies to those who had none, to evaluate the influence of concurrent peripheral neuropathies on the thenar muscular atrophy. Results: All ALS patients showed prolonged motor latencies and decreased sensory amplitudes in median nerve conduction study, compared to those in ulnar nerve conduction study. Healthy subjects did not show a difference between median and ulnar nerve conduction studies. The patients with ALS showed delayed latencies and amplitudes of median nerve CMAP, regardless of the presence of peripheral neuropathies. Conclusion: The selective thenar atrophy in ALS is prominently due to the pathophysiological disease progression, regardless of the presence of concomitant peripheral neuropathies.
Key Words: amyotrophic lateral sclerosis, peripheral nerve injuries, hand muscle atrophy, split hand


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