Radiation myelopathy (RM) is a relatively rare disorder characterized by white matter lesions of the spinal cord resulting from irradiation. It is divided into two forms by the latent periods: transient RM and delayed RM. The delayed RM develops usually non-transverse myelopathy symptoms such as dissociated sensory disturbance, unilateral leg weakness, and gait disturbance with asymmetric steps. Spinal MRI shows initially cord swelling and long T1/T2 intramedullary lesion with enhancement, then exhibits cord atrophy. Histopathological findings of delayed RM are white matter necrosis, demyelination, venous wall thickening and hyalinization. Glial theory and vascular hypothesis have been proposed to explain its pathophysiology. Several therapies such as adrenocorticosteroid, anticoagulation and hyperbaric oxygen have been tried to this disease with variable benefits. Radiation plexopathy is classified into two major types by the location: radiation-induced brachial plexopathy (BP) and radiation-induced lumbosacral plexopathy (LSP). The BP initially emerges as arm and shoulder pain, whereas LSP as leg weakness. Myokymia and fasciculations are observed in both types. Electrophysiological study reveals findings of peripheral neuropathy. It is often difficult to distinguish the radiation plexopathy from cancer invasion to the plexus, but MRI is useful to differentiate between these diseases. Pathological findings are small vessel obstruction, thick fibrosis, axonal degeneration and demyelination. Its pathomechanism is presumed that radiation-induced fibrous tissue compresses the nerve root as well as microvascular obstruction of the nerve. Adrenocorticosteroid and anticoagulation are considered as the strategy for symptomatic relief.

Shimazaki, Nakano, , , , , , , (2008). [Radiation myelopathy and plexopathy]. Brain and nerve = Shinkei kenkyu no shinpo, 2008 Feb;60(2):115-21. https://www.ncbi.nlm.nih.gov/pubmed/18306658