Absent Baseline Intraoperative Neuromonitoring Signals Part 2: Neuromuscular Scoliosis Current Concept Review

Abstract

Intraoperative neurologic monitoring (IONM) for neuromuscular scoliosis (NMS) is recommended to decrease risk of neurologic deficit. Transcranial motor evoked potentials (TcMEPs) increase sensitivity and reliability of signals in NMS patients, and are safe to perform even in patients with epilepsy. However, baseline neurologic and functional status, including weight bearing ability and residual motor function, are associated with ability to achieve baseline signals in NMS. Supratentorial brain lesions such as focal periventricular leukomalacia, hydrocephalus, and/or encephalomalacia may affect IONM signal acquisition.  When baseline signals are absent, troubleshooting can identify potentially modifiable anesthetic or technical neuromonitoring factors.  In patients with hydrocephalus, alternative wider electrode placement may facilitate successful TcMEP acquisition.

Families need to be counseled preoperatively that the baseline presence of IONM signals is variable, and that even in the setting of severe motor deficits, IONM can help preserve any functioning nerve pathways and residual motor function. Neurologic deficit can further compromise quality of life for patients and caregivers, as loss of protective sensory function increases risk of pressure ulcers. Loss of bowel and bladder function, including development of a neurogenic bladder or bowel in a previously incontinent child, can require use of catheterization. A clear plan should be formulated preoperatively to determine whether to proceed with surgery if IONM signals are absent or unreliable.