1cervical cord compressive myelopathy motor evoked potential

Transcranial Electrical Motor evoked potentials {TCeMEPs} are commonly being utilized in the intraoperative monitoring of the cervical cord compressive myelopathy or other region of spinal cord surgeries .TCeMEPs provides valuable information about the integrity of the motor pathways {Descending tract}

Parameters of Stimulation in cervical myelopathy.

Electrical stimulation.

Is typically delivered using a transcranial electrical stimulation through invasive corkscrew electrode, preferable montage to stimulate over the head at motor strip area C3-C4 or C4-C3 according to standard 10-20 EEG electrode placement system. [ Note given montage locates lateral side of homunculus which means hand area] .

Intensity of stimulation.

To be set at motor threshold levels to avoid inducing muscle contractions or movements that could interfere with the interpretation of MEP responses. The intensity is gradually increased until MEP responses are reliably elicited.

As per standard IONM machine.

A-Start with train of five pulses along 3-3.5 millisecond Inter stimulation interval [ISI] ,pulse duration 75 microsecond and intensity of stimulation start with 300-320 volt or changes of threshold will vary on subject/patient.

B– Start with double train five pulses + three pulses or 5+4 along with 2.5-3 millisecond Inter stimulation interval [ISI] ,pulse duration 75 microsecond to recruit maximum motor unit .

Recording Site.

MEP responses are typically recorded using electromyography (EMG) 3 centimeter long subdermal twisted needle electrodes placed on the patient’s limb’s muscles of interest, such as the Deltoid , Abductor Pollicis Brevis , Tibialis Anterior, Abductor Hallucis Brevis muscles Or other muscle recording can be modified as per surgical level.

How to Interpret the signals .

The surgical neurophysiologist team carefully monitors and interprets the MEP responses usually >50 reduction amplitude and 10% latency prolong or all and none [Note in my experience i usually observe number of phase of waveform like polyphasic waveform if become monophasic which is significant and secondary amplitude] especially this type of findings may reflect in chronic compressive cervical cord myelopathy.

Drop signals of potentials.

Above given parameters is vary on patients, like grade of cervical cord myelopathy/compression.