AAEM minimonograph #35: Clinical experience with transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Neurology
• Clinical Neurophysiology

Background:

• Motor evoked potentials (MEPs) are crucial for evaluating the integrity of the corticospinal tract.
• Understanding normative MEP values and age-related changes is essential for accurate clinical interpretation.
• Previous studies have explored MEPs in specific neurological disorders, but a comprehensive analysis across a wide range of conditions and ages is needed.

Purpose of the Study:

• To establish normative data for MEPs in a large, age-diverse cohort.
• To investigate the impact of aging on MEP parameters.
• To assess the diagnostic utility of MEPs in various neurological diseases.

Main Methods:

• Transcranial magnetic stimulation was used to elicit MEPs in 150 healthy controls (aged 14-85) and 275 patients with diverse neurological conditions.
• Key MEP parameters measured included cortex-to-muscle latency, central motor delay, and MEP amplitude.
• MEP data were analyzed in relation to age and specific disease diagnoses.

Main Results:

• MEP latency increases linearly with age, and central motor delay is prolonged in older individuals.
• Compound muscle action potentials and MEP amplitudes decrease linearly with age.
• Abnormal MEPs were frequently observed in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS), with MEPs showing greater sensitivity than somatosensory evoked potentials (SEPs) in MS.
• MEPs demonstrated utility in identifying conduction abnormalities in demyelinating neuropathies and plexopathy.

Conclusions:

• MEPs are a safe and valuable neurophysiological tool for assessing motor pathway function.
• Age-related changes in MEPs are significant and should be considered in clinical assessments.
• MEPs provide sensitive diagnostic information for various neurological disorders, including MS, ALS, and neuropathies.