[Characteristics of repetitive nerve stimulation in 53 cases of amyotrophic lateral sclerosis]

Objective: To investigate the feature of repetitive nerve stimulation (RNS) in patients with amyotrophic lateral sclerosis (ALS) and correlation between RNS and clinical features and electromyography (EMG) findings of the corresponding muscle. Methods: Needle EMG and RNS were performed in 53 patients with ALS, who were recruited into Department of Neurology of Chinese PLA general hospital during April to December in 2016. Decrement of the compond muscle action potential (CMAP) in response to RNS of different nerves and stimulus frequencies was compared. The effects of gender, age of onset, disease duration, region of onset, ALS functional rating scale-revised (ALSFRS-R) and rate of disease progression (ΔFS) on the decrement were analyzed. Results: 49.1% of patients with ALS had decremental responses to low frequency RNS (LF-RNS) in accessory nerve, which was lower in ulnar nerve (4.3%) and common peroneal nerve (2.6%). Decremental responses of accessory nerve at 3 Hz were observed in 49.1% of patients with ALS, more frequent than 30.2% at 1 Hz. None of the patients had increased responses to high frequency RNS. Patients with upper-limb-onset, longer disease duration and lower ALSFRS-R tended to have more frequent decrement of CMAP in response to RNS. The decrement with LF-RNS of accessory nerve was in concert with neurogenic damage of sternocleidomastoid muscle with needle EMG (r=0.365, P=0.007). There were 3 patients who had decremental responses to LF-RNS in accessory nerve without clinical involvement and neurogenic damage of sternocleidomastoid muscle. Conclusions: There is significant decrement of CMAP in response to LF-RNS of accessory nerve in patients with ALS, which may reveal neuromuscular junction (NMJ) impairment. It may indicated a dying-back pattern of disease progression which derived from motor neuron terminal or NMJ to neuronal soma that some patients with ALS have decremental responses in RNS without clinical involvement and neurogenic damage of sternocleidomastoid muscle.