Correlation between decremental responses in repetitive nerve stimulation and disease progression rate in patients with amyotrophic lateral sclerosis.

Objective: Decrement responses in repetitive nerve stimulation (RNS) are theoretically expected to correlate with the disease progression speed in amyotrophic lateral sclerosis (ALS). However, actual results have been controversial. We investigated this issue using ΔFS calculated from the ALS functional rating scale revised version (ALSFRS-R) and the duration of illness. Methods: RNS results of the abductor pollicis brevis, trapezius, and deltoid muscles in our previous study were reviewed. We investigated correlations and multiple regressions regarding decremental percentage (Decr%), the amplitude of the initial compound muscle action potential (Amp), and progression speed parameters, i.e. ΔFS or ΔUL-FS, the latter being the ΔFS for the upper-limb questions in ALSFRS-R. Results: Included subjects were 124 patients with ALS, 47 of whom were upper-limb onset. Multiple regression analyses revealed that Decr% is largely determined by Amp and that Δ FS or ΔUL-FS showed no or little contributions to Decr%. Conclusions: Decremental responses in RNS does not predict the speed of progression of the functional impairment in patients with ALS. Significance: This study suggests that the decremental responses in RNS in ALS are contributed by the impaired neuromuscular transmission in chronic sprouts following extensive reinnervation, as well as by the immature sprouts.