Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis

Area of Science:

• Neurology
• Neurophysiology
• Electromyography

Background:

• Decremental responses during low-frequency repetitive nerve stimulation (LF-RNS) are common in amyotrophic lateral sclerosis (ALS) patients.
• The underlying pathological mechanisms for these decremental responses in ALS remain unclear.
• This study investigates the characteristics of RNS in a cohort of Chinese ALS patients.

Purpose of the Study:

• To characterize the features of repetitive nerve stimulation (RNS) in Chinese patients diagnosed with amyotrophic lateral sclerosis (ALS).
• To explore the potential implications of RNS findings on the understanding of ALS pathophysiology.

Main Methods:

• Retrospective analysis of clinical and electrophysiological data from 146 probable and definite ALS patients who underwent RNS.
• Low-frequency RNS (LF-RNS) at 3 Hz was applied to trapezius, deltoid, abductor digiti minimi (ADM), quadriceps femoris, and tibialis anterior muscles.
• High-frequency RNS (HF-RNS) at 10 Hz was performed exclusively on the ADM.
• Statistical analysis included two-sample t-tests and Chi-squared tests.

Main Results:

• Decremental responses (≥10%) to LF-RNS were observed in 56.8% of patients, most frequently in the trapezius and deltoid muscles.
• A higher incidence of decremental responses was noted in patients with upper limb onset ALS.
• Incremental responses (≥60%) to HF-RNS in the ADM occurred in 5.6% of cases.
• Among muscles with decremental responses, a continuous pattern was more prevalent (57.4%) than a U-shape pattern (34.3%).
• Nineteen cases exhibited definite decrements in trapezius LF-RNS tests, with no abnormalities found in accessory nerve-innervated muscles.

Conclusions:

• Repetitive nerve stimulation (RNS) commonly reveals decremental responses in amyotrophic lateral sclerosis (ALS) patients.
• Findings in the trapezius muscle suggest a potential 'dying back' process, where neuromuscular junction (NMJ) destruction precedes motor neuron degeneration in some ALS cases.
• Incremental responses in the ADM indicate damage affecting both pre- and postsynaptic membranes of the neuromuscular junction.