Patient Factors Impacting Baseline Motor Evoked Potentials (MEPs) in Patients Undergoing Cervical Spine Surgery for Myelopathy or Radiculopathy

Study Design: Retrospective review of 2532 adults who underwent elective surgery for cervical radiculopathy or myelopathy with intraoperative neuromonitoring (IONM) with motor evoked potentials (MEPs) between 2017 and 2019. Objective: Evaluate attainability of monitorable MEPs across demographic, health history, and patient-reported outcomes measure (PROM) factors. Summary of Background Data: When baseline IONM responses cannot be obtained, the value of IONM on mitigating the risk of postoperative deficits is marginalized and a clinical decision to proceed must be made based, in part, on the differential diagnosis of the unmonitorable MEPs. Despite known associations with baseline MEPs and anesthetic regimen or preoperative motor strength, little is known regarding associations with other patient factors. Methods: Demographics, health history, and PROM data were collected preoperatively. MEP baseline responses were reported as monitorable or unmonitorable at incision. Multivariable logistic regression estimated the odds of having at least one unmonitorable MEP from demographic and health history factors. Results: Age [odds ratio (OR)=1.031, P<0.001], sex (male OR=1.572, P=0.007), a primary diagnosis of myelopathy (OR=1.493, P=0.021), peripheral vascular disease (OR=2.830, P=0.009), type II diabetes (OR=1.658, P=0.005), and hypertension (OR=1.406, P=0.040) were each associated with increased odds of unmonitorable MEPs from one or more muscles; a history of thyroid disorder was inversely related (OR=0.583, P=0.027). Patients with unmonitorable MEPs reported less neck-associated disability and pain (P<0.036), but worse SF-12 physical health and lower extremity (LE) and upper extremity function (P<0.016). Compared with radiculopathy, unmonitorable MEPs in myelopathy patients more often involved LE muscles. Cord function was monitorable in 99.1% of myelopathic patients with no reported LE dysfunction and no history of hypertension or diabetes. Conclusion: Myelopathy, hypertension, peripheral vascular disease, diabetes, and/or symptomatic LE dysfunction increased the odds of having unmonitorable baseline MEPs. Unmonitorable baseline MEPs was uncommon in patients without significant LE weakness, even in the presence of myelopathy.