Frequency-dependent conduction delay of motor-evoked potentials in multiple sclerosis

Area of Science:

• Neuroscience
• Neurology

Background:

• Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system.
• Abnormalities in neuronal conduction are characteristic of MS pathology.
• Transcranial magnetic stimulation (TMS) is a valuable tool for assessing central motor conduction pathways.

Purpose of the Study:

• To investigate central motor conduction time (CMCT) alterations in multiple sclerosis (MS) patients using paired transcranial magnetic stimulation (TMS).
• To determine the origin of conduction delays observed in MS patients.

Main Methods:

• Paired TMS was administered to 33 MS patients and 21 healthy controls.
• Motor-evoked potentials (MEPs) were recorded to assess latency and CMCT at various interstimulus intervals (ISIs).
• The effect of voluntary muscle contraction and stimulation intensity on conduction delay was examined.

Main Results:

• MS patients showed significantly prolonged CMCT at ISIs of 75, 100, and 150 ms compared to controls.
• Voluntary muscle contraction normalized MEP latency differences in MS patients.
• No correlation was found between single TMS-induced prolonged CMCT and frequency-dependent delays in MS patients.

Conclusions:

• Paired TMS reveals significant conduction delays in MS patients, indicative of central nervous system dysfunction.
• The findings suggest that the observed conduction delay in MS is likely of cortical origin.
• Abnormalities in ascending volleys to the neocortex may underlie these TMS-detected conduction abnormalities in MS.