Decremental Responses to Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis

Abstract

Introduction: 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. Methods: We retrospectively analyzed relationship between clinical features and the decremental response in RNS in 184 sporadic ALS patients. Results: (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). Conclusions: 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.

Can the Large-Scale Decrement in Repetitive Nerve Stimulation Be Used as an Exclusion Criterion for Amyotrophic Lateral Sclerosis?

“…Moreover, this study showed that the onset of ALS did not affect the RNS decrement responses, which was consistent with previous research (8,18). However, some studies have shown that patients with upper limb onset had higher decremental percentages compared with those with other sites of onset (7,17). The underlying reason for these differences is unclear.…”

“…Furthermore, more than 10% of the patients had a decrement of ≥20%. Although it has also been reported previously that the decremental percentage can reach 20% (4,7,8), the proportion of patients with such a characteristic was not mentioned. If the current electrophysiological diagnostic criteria were applied, more than 10% of ALS patients would be misdiagnosed.…”

“…The ALSFRS-R score, as a significant predictor of prognosis, was extensively applied to assess the severity of the disease (7). The patients in the positive decrement group had lower ALSFRS-R scores compared with those in the decremental negative group, suggesting that the former were worse.…”

“…The patients in the positive decrement group had lower ALSFRS-R scores compared with those in the decremental negative group, suggesting that the former were worse. Some studies have shown that the disease progressed more rapidly in ALS patients with a positive decrement (4,8,13,14), but others contradicted this (5,7,(15)(16)(17). If the RNS decrement responses were not related to the disease progression, the interpretation of the mechanism of decrement responses, the early neural reinnervation, may need to be corrected (5).…”

“…The electrophysiological diagnostic criteria of ALS revised by the World Federation of Neurology Research Group on Motor Neuron Diseases pointed out that a significant compound muscle action potential (CMAP) decrement >20% in RNS was a diagnostic exclusion criterion for ALS (6). However, later studies demonstrated that a decrement >20% was observed in ALS patients (4,7,8). So far, none of the published studies has indicated the proportion of patients with a decrement of 20% or greater.…”