Is Intraoperative Muscle Motor Evoked Potential Variability due to Fluctuating Lower Motor Neuron Background Excitability?

Purpose: This pilot study tests the contribution of fluctuating lower motor neuron excitability to motor evoked potential (MEP) variability.

Methods: In six pediatric patients with idiopathic scoliosis and normal neurologic examination, cascades of 30 intraoperative H-reflexes (HRs) and MEPs were evoked in the soleus muscle using constant-current stimulators and recorded through surface electrodes with a 20-second interstimulus interval. First, HRs were obtained with an intensity capable of evoking the maximum response.