Absent Baseline Intraoperative Neuromonitoring Signals Part 2: Neuromuscular Scoliosis

Transcranial motor evoked potentials (TcMEPs) increase sensitivity and reliability of signals in neuromuscular scoliosis (NMS) patients and are safe to perform even in patients with epilepsy. Baseline neurologic and functional status, including weight-bearing ability and 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 without IONM signals, risk of neurologic deficit increases to 5%. This can 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, 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. Key Concepts: • Intraoperative neuromonitoring with TCMEPS and SSEPS is recommended during spinal fusion for neuromuscular patients, including severely affected GMFCS IV and V spastic quadriplegic CP patients with epilepsy. • Presence of supratentorial brain lesions, antiepileptic use, and baseline neurologic and functional status, especially weight-bearing ability and baseline motor function, are associated with ability to achieve signals. • Preoperative evaluation and discussion with family is imperative for decision-making when IONM signals are absent and include anticipated risks of curvature progression without surgery versus 5% risk of neurologic deficit from surgery. • Loss of protective sensory function increases risk of pressure ulcers, while loss of bowel and bladder function can cause development of a neurogenic bladder or bowel, which can be detrimental to quality of life.