Decremental Responses to Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis

To illuminate the mechanism of neuromuscular junction involvement by analyzing the features of a slow-rate repetitive nerve simulation (RNS) and EMG in amyotrophic lateral sclerosis (ALS) patients.

We retrospectively analyzed relationship between clinical features and the decremental response in RNS in 184 sporadic ALS patients.

(1) 44.3 and 43.5% of compound muscle action potentials (CMAP) decrement were more than -10% in deltoid muscle (Del) and Trap; (2) ALS patients were divided into RNS positive (RNS+) and RNS negative (RNS-) group according to decremental percentage of RNS greater or less than -10%. The diagnostic delay time was shorter and ALSFRS-r score was lower in RNS+ than RNS- group (p < 0.05), progression rate had no difference. The incidence of RNS+ decrement was higher in cervical enlargement onset and definite diagnostic degrees (p < 0.05); (3) In EMG+ group, the CMAP amplitude was lower (Axillary: 3.1 ± 1.91 vs. 5.92 ± 2.896, p = 0.000; Accessory: 2.68 ± 1.349 vs. 3.65 ± 1.53, p = 0.002), decremental percentage of RNS was higher (Axillary: -10.85 ± 7.508 vs. -5.43 ± 8.425, p = 0.000; Accessory: -13.11 ± 7.539 vs. -8.03 ± 5.999, p = 0.000) compared with needle EMG- group whether in Del or Trap; (4) Decremental response of RNS was positively correlated with the CMAP amplitude in Axillary and Accessory nerves (R = 0.201, p < 0.0001; R = 0.103, p < 0.0001).

Our clinical results support the mechanism of decremental phenomenon of RNS is immature sprouts and unstable conduction by the degenerating axons in ALS patients. The more serious the axon damage, the more significant the RNS decremental response. But decremental response dose not effect disease progression.