Spinal Cord and Peripheral Nervous System

Abstract

Abstract Spinal cord and peripheral nerve injury (myelopathy), from radiation therapy can be transient or severe and debilitating, producing pain, paresthesias, sensory deficits, paralysis, Brown-Sequard syndrome, and bowel/bladder incontinence. The sympathetic system, the ganglia are located along paired chains on both sides of the vertebral column (the sympathetic trunk), as well as in three major collateral ganglia. The principal pathogenesis of injury is established to be due to vascular endothelial damage, glial cell injury, or both. Peripheral nerve damage by ionizing radiation has focused on the effect of single, high doses of radiation in animals, simulating the experience of intraoperative radiotherapy. Approximately 15 Gy IORT alone was observed to produce a 50 % reduction in the axon/myelin content. Magnetic resonance imaging (MRI) is typically the imaging modality of choice for assessing malignancies involving the spinal cord and brachial plexuses and detecting and diagnosing cord myelopathy. The use of various chemotherapy agents during radiotherapy has been shown to increase the radiosensitivity of the spinal cord. Toxicity increases when intrathecal chemotherapy is combined with systemic therapy with CNS irradiation. Radiation therapy to the spinal cord and peripheral nerves can induce myelopathy, typically characterized by pain, paralysis, and paresthesias. The risk of myelopathy primarily depends on the total radiation dose and dose per fraction, although the volume irradiated, underlying disease, concurrent therapies, and previous irradiation may also play a role. For external beam radiotherapy (EBRT) to the spinal cord in 2 Gy daily fractions, the risk of myelopathy appears low (<0.2 %) at 50 Gy and modest (<10 %) at 60 Gy, with an approximately 50 % risk of myelopathy at 70 Gy. Due to the severe consequences of myelopathy, clinical dose limits, i.e., shield at 40 Gy, have been used which carry a low (<0.2 %) risk of toxicity. The risk of radiation-induced brachial plexopathy is <1 % for a total dose of 50 Gy or less. For intraoperative radiotherapy (IORT) to the lumbosacral and brachial plexus, the threshold dose for injury appears to be 15–20 Gy. For single-fraction stereotactic radiosurgery to the spine, the risk of radiation-induced myelopathy appears low (well under 5 %) when the maximum point dose to the cord is ≤14 Gy, though the number of patients is small and the follow-up short at present. KeywordsAutonomic nervous systemBrachial plexusHypofractionationIntraoperative radiotherapyMyelopathyNeuropathyParasympathetic divisionRadiosurgerySpinal cordStereotactic body radiotherapySympathetic division