This test is used to determine the conductivity of the motor nerve tracts, i.e. the nerve pathways that run from the brain via the spinal cord and peripheral nerves to the muscles. This allows assessments to be made of the motor nerves in the brain and spinal cord (central nerve pathways) in addition to the values measured during electroneurography (peripheral nerve pathways).
Magnetic stimulation involves holding a magnetic coil above the patient’s head. This coil emits a magnetic pulse that briefly stimulates the underlying motor nerve cells. A muscle twitch is triggered and registered in the arms or legs via attached electrodes. The time between the impulse being delivered over the head or spine and the muscle twitch that occurs is measured. In this way, it can be determined whether there is a dysfunction of the motor nerve pathways.
Magnetic stimulation is not painful, but the test is occasionally experienced as unpleasant due to the sudden impulses and muscle twitching. The examination is performed in a sitting position. The patient is asked to slightly tense the muscle to which the electrodes are attached. Otherwise, they should remain relaxed and sit quietly.
The examination is not dangerous, but should not be performed on patients with epilepsy, those with metal components inside the head (e.g., metal splinters in the eye or certain clips after head surgery), during pregnancy, or on people with pacemakers or neurostimulators.
Often, somatosensory evoked potentials (SSEPs), which run in the opposite direction in the sensory nervous system, are also examined as a supplement to MEPs. Both examinations can also be performed by neurologists for continuous monitoring of the nervous system during operations, for example on the spine. These techniques then form part of intraoperative neuromonitoring (IOM).
The entire examination takes about 20-45 minutes.
