放射線照射による脊髄障害と神経叢障害

Radiation Myelopathy and Plexopathy

Ⅰ．放射線神経障害

　がん治療のため放射線照射を行った場合，それが原因で神経系に障害をきたすことがある。神経系の放射線障害は，その神経障害部位から放射線脳障害，放射線脊髄症，放射線末梢神経障害に大きく分けられる。また，障害の経過からは，放射線照射後数日から数カ月して起こり，一過性で1～9カ月（平均3カ月）で自然寛解する急性一過性放射線障害と，照射後6カ月以降に生じる難治性の慢性進行性放射線神経障害に分類される^1）。本稿では，主として遅発性放射線脊髄障害と，末梢神経障害について概説する。

Abstract

　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.