Neuromuscular Electrical Stimulation Does Not Influence Spinal Excitability in Multiple Sclerosis Patients

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Clinical Electrophysiology

Background:

• Neuromuscular electrical stimulation (NMES) offers functional benefits for Multiple Sclerosis (MS) patients.
• The underlying neurophysiological mechanisms of NMES-induced functional improvements in MS remain largely unknown.
• Spinal excitability, assessed via the soleus Hoffmann reflex (H-reflex), is a key indicator of neural pathway function.

Purpose of the Study:

• To compare acute spinal excitability responses between MS patients and healthy controls.
• To investigate H-reflex modulation under passive NMES (pNMES), NMES with voluntary contraction (NMES+), and voluntary contraction (ISO) conditions.
• To elucidate the neurophysiological mechanisms of NMES in MS by examining H-reflex changes.

Main Methods:

• Twenty MS patients and 20 healthy controls participated in a single experimental session.
• Participants underwent three conditions: pNMES, NMES+, and ISO, each involving 15 repetitions of 6-second contractions at 20% maximal voluntary isometric contraction.
• H-reflex amplitudes were measured before and after each experimental condition.

Main Results:

• MS patients exhibited no significant changes in H-reflex amplitude across all three conditions (ISO, pNMES, NMES+).
• Healthy controls showed a significant H-reflex increase under NMES+ and a significant decrease under pNMES.
• H-reflex amplitude remained unchanged in healthy controls during the ISO condition.

Conclusions:

• The distinct H-reflex responses between MS patients and healthy controls suggest a compromised ability in MS to modulate spinal excitability.
• These findings highlight potential neurophysiological differences in response to NMES between individuals with and without MS.
• Further research is warranted to understand the implications of impaired spinal excitability modulation for NMES efficacy in MS rehabilitation.