From the Guidelines
Motor evoked potentials (MEPs) normative data should be established by each neurophysiology laboratory using at least 30-50 healthy subjects across different age groups, considering factors such as muscle being tested, stimulation parameters, and recording techniques. When interpreting MEPs clinically, it is crucial to consider the variability in central motor conduction time (CMCT) and amplitude values, which can be influenced by age, height, and temperature 1. For reliable clinical interpretation, the following guidelines can be followed:
- Upper limb CMCT typically ranges from 5-8 ms, while lower limb CMCT ranges from 10-15 ms
- Amplitude values generally fall between 1-10 mV for distal hand muscles
- A side-to-side difference in CMCT greater than 2 ms or an absolute CMCT exceeding the upper limit of normal by more than 2.5 ms is generally considered abnormal
- Temperature control is essential during testing, as hypothermia can falsely prolong conduction times The importance of establishing a normative database is highlighted by the fact that equipment and methodology differences can significantly impact measurements, and this data provides the foundation for detecting abnormalities in patients with suspected corticospinal tract pathology 1. In the context of thoracic aortic disease management, monitoring of MEPs has become common due to its ability to provide real-time feedback on spinal cord function, allowing for prompt intervention in case of neurologic compromise 1. It is essential to recognize the limitations of SSEP monitoring, which may not detect isolated anterior column injuries, and the importance of combining MEP monitoring with other neuroprotective strategies to minimize the risk of neurologic complications 1.
From the Research
Motor Evoked Potentials Normative Data
- Motor evoked potentials (MEPs) are a useful tool for assessing the integrity of the descending corticospinal tract in the laboratory 2.
- MEPs have been used to assess motor pathways dysfunction in multiple sclerosis (MS) patients, with studies showing that MEP parameters such as amplitude and area are altered in MS patients, even in those with no or minor neurological signs 3.
- The use of MEPs in clinical trials for MS has been proposed, with standardized multicenter EP assessment with central reading demonstrated to be feasible and reliable 2.
- MEPs have been shown to be a highly accurate diagnostic test, with a high sensitivity in spinal cord disorders, hereditary spastic paraplegia, and motor neuron diseases 4.
- The diagnostic value of MEPs has been assessed in a prospective study of 1023 neurological patients, with an agreement index between electrophysiological and clinical findings of 87% and an overall accuracy of 0.97 4.
MEP Parameters
- MEP parameters such as motor thresholds, central motor conduction time (CMCT), amplitude, and area have been measured in studies 3, 5.
- The amplitude and area of MEPs have been shown to be altered in MS patients, with a higher percentage of patients having amplitude or area alterations compared to CMCT alterations 3.
- The use of threshold-level alarm criteria for interpreting MEPs during surgery has been proposed, with significant increases in target muscle thresholds often noted many minutes or hours before complete signal loss 5.
Clinical Applications
- MEPs have been used in clinical trials for MS, with the potential to measure neuroprotection and remyelination resulting from drugs 2.
- The use of MEPs in the diagnosis of MS and other neurological disorders has been established, with a high sensitivity and specificity in detecting motor pathways dysfunction 3, 4.
- MEPs have been used to monitor the effects of drugs used to treat MS, with the potential to be used as a measure of efficacy in clinical trials testing neuroprotective agents 2.