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Updated: Apr 28, 2026
Utility of Dissociated Intrinsic Hand Muscle Atrophy in the Diagnosis of Amyotrophic Lateral Sclerosis
Published on: March 4, 2014
[Clinical and neuro electrophysiologic study of flail arm syndrome]
Ying-sheng Xu1, Dong-sheng Fan
1Department of Neurology, Peking University Third Hospital, Beijing, China.
Objective:
To explore the clinical and neuroelectrophysiological characteristics of flail arm syndrome (FAS).
Methods:
The clinical and neuroelectrophysiological characteristics were analyzed retrospectively from July 1, 2006 to July 1, 2012 in FAS patients (n = 56), those with upper limb onset amyotrophic lateral sclerosis (ALS) (n = 60) and those with upper brachial plexus neuropathy (n = 22) from our hospital. Nerve conduction study of musculocutaneous, axillary, median, ulnar, radial, tibial, peroneal and sural nerves and electromyogram (EMG) of bulbar, cervical, thoracic and lumbosacral regions were conducted.
Results:
In FAS patients, the ratio of male-to-female was 5:1 and they were characterized by symmetric, proximal wasting and weakness of upper extremities, the involved muscles demonstrated neurogenic damage on EMG and the amplitude of compound muscle action potential (CMAP) of arms decreased. Compared with ALS patients, the amplitude of motor unit action potential (MUAP) of deltoid muscle and biceps muscle was higher in FAS patients ((1531 ± 76) vs (898 ± 57) µV; (1433 ± 57) vs (872 ± 75) µV) (F = 13.25, 6.33; P < 0.05). Compared with upper brachial plexus neuropathy patients, the amplitude of MUAP of first dorsal interosseous, deltoid and biceps muscles was higher in FAS patients ((1263 ± 24) vs (507 ± 42) µV; (1531 ± 76) vs (564 ± 27) µV; (1433 ± 57) vs (593 ± 36) µV) (F = 12.32, 16.71, 8.35; P < 0.05).
Conclusion:
The clinical manifestations of FAS are symmetric, proximal wasting and weakness of arms. And the involved muscles show denervation on EMG and the amplitudes of CMAPs decrease in motor nerves of upper extremities.
