Study on variation trend of repetitive nerve stimulation waveform in amyotrophic lateral sclerosis

Abstract

Background: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease involving both upper and lower motor neurons with no effective cure. Electrophysiological studies have found decremental responses during low-frequency repetitive nerve stimulation (RNS) except for diffused neurogenic activities. However, the difference between ALS and generalized myasthenia gravis (GMG) in terms of waveform features is unclear. In the current study, we explored the variation trend of the amplitudes curve between ALS and GMG with low-frequency, positive RNS, and the possible mechanism is discussed preliminarily.

Methods: A total of 85 ALS patients and 41 GMG patients were recruited. All patients were from Peking Union Medical College Hospital (PUMCH) between July 1, 2012 and February 28, 2015. RNS study included ulnar nerve, accessory nerve and facial nerve at 3 Hz and 5 Hz stimulation. The percentage reduction in the amplitude of the fourth or fifth wave from the first wave was calculated and compared with the normal values of our hospital. A 15% decrease in amplitude is defined as a decrease in amplitude.

Results: The decremental response at low-frequency RNS showed the abnormal rate of RNS decline was 54.1% (46/85) in the ALS group, and the results of different nerves were 54.1% (46/85) of the accessory nerve, 8.2% (7/85) of the ulnar nerve and 0% (0/85) of the facial nerve stimulation, respectively. In the GMG group, the abnormal rate of RNS decline was 100% (41/41) at low-frequency RNS of accessory nerves. However, there was a significant difference between the 2 groups in the amplitude after the sixth wave.

Conclusions: Both groups of patients are able to show a decreasing amplitude of low-frequency stimulation RNS, but the recovery trend after the sixth wave has significant variation. It implies the different pathogenesis of NMJ dysfunction of these 2 diseases.

Figure 1

Descent pattern of low-frequency RNS in GMG patients. (A) and (B) are the results of the accessory nerve stimulation RNS in a GMG patient. There is an obvious decreasing amplitude at 5 Hz stimulation, but the fifth wave starts to rise significantly. CMAP: Compound muscle action potential; GMG: Generalized myasthenia gravis; RNS: Repetitive nerve stimulation.

Figure 2

Descent pattern of low-frequency RNS in ALS patients. (A) and (B) are the results of the accessory nerve stimulation RNS in an ALS patient. There is an obvious decreasing amplitude at 5 Hz stimulation, but no obvious rebound after the fifth wave. ALS: Amyotrophic lateral sclerosis; CMAP: Compound muscle action potential; RNS: Repetitive nerve stimulation.

Figure 3

RNS in accessory nerve. There are remarkable decremental responses at either 3 Hz (A) and 5 Hz (B) accessory nerve stimulation RNS. The lowest was found in 4th and 5th. After the waves gradually pick up and the waveform looks like “U” in GMG patients. The waveform looks like “L” in ALS patients. ALS: Amyotrophic lateral sclerosis; GMG: Generalized myasthenia gravis; RNS: Repetitive nerve stimulation.

Figure 4

RNS in ulnar nerve. There are remarkable decremental responses at either 3 Hz (A) or 5 Hz (B) ulnar nerve stimulation RNS. The lowest was found in 4th and 5th. After the waves gradually pick up and the waveform looks like “U” in GMG patients. The waveform looks like “L” in ALS patients. ALS: Amyotrophic lateral sclerosis; GMG: Generalized myasthenia gravis; RNS: Repetitive nerve stimulation.

Figure 5

Amplitude ratio curve of ALS's accessory nerve and ulnar nerve. For ALS patients’ accessory nerves (A) and ulnar nerve (B), the lowest CMAP appeared in the 4th or 5th one at 3 Hz or 5 Hz RNS, there was no significant recovery after the nadir of decrement. ALS: Amyotrophic lateral sclerosis; CMAP: Compound muscle action potential; GMG: Generalized myasthenia gravis; RNS: Repetitive nerve stimulation.

Figure 6

Amplitude ratio curve of GMG's accessory nerve, ulnar nerve. For GMG's accessory nerve (A) and ulnar nerve (B), the lowest CMAP emerged in the 4th or 5th one at low-frequency RNS, there was slow recovery after the nadir of decrement from the 6th or 7th CMAP. ALS: Amyotrophic lateral sclerosis; CMAP: Compound muscle action potential; GMG: Generalized myasthenia gravis; RNS: Repetitive nerve stimulation.