Analysis of the characteristics of patients with amyotrophic lateral sclerosis with neuromuscular junction dysfunction prior to motor neuron degeneration

Abstract

Objective: To investigate the clinical and electrophysiological characteristics of patients with amyotrophic lateral sclerosis (ALS) with positive repetitive nerve stimulation (RNS) test results on the accessory nerve and negative needle electromyography (EMG) test results on the sternocleidomastoid with the goal to enrich the knowledge of disease progression in patients with ALS. Methods: The clinical data of 612 patients diagnosed with ALS at the Neurology Department of the First Medical Center, Chinese PLA General Hospital from June 2016 to August 2022 were collected. In total, 267 cases had undergone EMG tests on the sternocleidomastoid following a positive 3 Hz RNS test result on the accessory nerve, who were selected as the study subjects. The differences in clinical indicators were compared between RNS (+)/EMG (-) group and RNS (+)/EMG (+) group. A binomial distribution model with multiple variables was built to quantitatively analyze the major factors and their effects. Results: At the initial visit, 15.8% of patients with ALS were 3 Hz RNS (+) on the accessory nerve and EMG (-) on the ipsilateral sternocleidomastoid, accounting for 36.3% of RNS (+) patients. The decremental range of the 3 Hz RNS test delivered to the accessory nerve in these patients [-14% (-19%, -12%)] was lower than that in patients with RNS (+)/EMG (+) [-17% (-23%, -13%)] (P<0.05), while the ratio of upper limb onset (64.9%) and non-definite diagnosis (28.9%) were higher [54.7% and 13.5% for patients with RNS (+)/EMG (+), P<0.05]. Furthermore, the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) score [40 (37, 42)], body mass index (BMI) [23.8 (22.0, 25.4) kg/m2] and forced vital capacity (FVC) [92.8% (76.6%, 103.8%)] were higher in patients with RNS(+)/EMG(+) (P<0.05). The multivariate model suggested that, in patients with RNS (+)/EMG (-), the ratio of upper limb onset to lower limb onset was 1.04, while that of upper limb onset to bulbar onset was 2.02, and that of lower limb onset to bulbar onset was 1.94. The ratio of non-definite ALS to definite ALS was 1.13. The ALSFRS-R score, BMI, and FVC had a protective contribution to the electrophysiological function of the motor neurons. The ratio of the effect size of the ALSFRS-R or BMI to that of FVC was 3.37 and 1.14, respectively. Conclusions: Patients with ALS that were 3 Hz RNS (+) on the accessory nerve and EMG (-) on the ipsilateral sternocleidomastoid had a smaller decremental range of the compound muscle action potential amplitude, and a higher proportion of upper limb onset and non-definite ALS. A higher ALSFRS-R score, BMI, and FVC have a protective effect to the electrophysiological function of motor neurons. The effect size of the ALSFRS-R score is the largest, followed by BMI and FVC.