Do neurogenic lesions of the spinal cord generate distinctive features of the epidurally recorded motor evoked potential?

Abstract

Since the introduction of intraoperative motor evoked potential (MEP) monitoring, MEPs have been recorded from many different patient populations. The best available method of monitoring MEPs in the operating room is recording from the epidural space of the spinal cord after transcranial electrical stimulation of the motor cortex¹. Epidurally recorded MEPs are characterized by a D-wave, which represents the response following direct stimulation of the corticospinal tract. This wave may be followed by one or more I-waves, which represent the response following indirect (transynaptic) activation of the cortical motoneurons. The D-wave is the response of principal interest in intraoperative monitoring; it consists of a single, stable positive-negative component, exhibiting a similar morphology in most patients. In contrast, the I-wave complex shows characteristics which vary greatly across different patient populations; it may be absent or consist of one to four positive-negative components.