Damage to the Nervous System Due to Radiation Therapy
Radiation therapy is one component in the treatment of tumors of the nervous system. It is directed at the general area (such as the whole head) when people have several tumors or a tumor that does not have distinct borders. When the tumor has distinct borders, therapy can be directed specifically at the tumor.
Radiation from these treatments sometimes damages the nervous system, despite the best efforts to prevent damage (see Overview of Imaging Tests : Risks of Radiation in Medical Imaging).
Whether damage occurs and how severe it is depend on several factors:
Symptoms of radiation damage can develop in the first few days (acute) or months of treatment (early-delayed) or several months or years after treatment (late-delayed). Symptoms can remain the same or worsen and can be temporary or permanent.
Acute encephalopathy can result from radiation to the brain. Fluid accumulates within the cells of the brain, causing the entire brain to swell (called cerebral edema). Symptoms include headaches, nausea, vomiting, drowsiness, and confusion. Acute encephalopathy usually begins shortly after the first or second dose of radiation is given. Usually, symptoms diminish during the radiation treatments. Corticosteroids such as dexamethasone may help prevent or reduce cerebral edema.
Early-delayed radiation damage causes symptoms similar to those of acute encephalopathy. Symptoms usually diminish on their own over several days to weeks, sometimes more rapidly if corticosteroids are used.
If radiation is directed at the spine in the neck or upper back, early-delayed radiation myelopathy may develop. This disorder sometimes causes a sensation similar to an electric shock. The sensation begins in the neck or back, usually when the neck is bent forward, and shoots down to the legs. This disorder usually resolves without treatment.
Late-delayed radiation damage causes symptoms many months or years after radiation therapy. Many children and adults who receive whole-head brain radiation therapy develop late-delayed toxicity if they survive long enough. The most common cause in children is radiation therapy to prevent leukemia or to treat a type of brain tumor called medulloblastoma. Symptoms include progressively worsening dementia, memory loss, difficulty thinking, mistaken perceptions, personality changes, and, in adults, unsteadiness in walking.
After radiation therapy for tumors near the spine, late-delayed myelopathy may develop. This disorder causes weakness, loss of sensation, and sometimes the Brown-Séquard syndrome. In this syndrome, one side of the spinal cord is damaged, resulting in weakness on one side of the body and loss of pain and temperature sensation on the other side. On the weak side of the body, people may be unable to sense where their hands and feet are without looking at them (position sense). Late-delayed radiation myelopathy usually does not subside and often results in paralysis.
Nerves near the site of the radiation therapy may also be damaged. For example, radiation to a breast or lung may damage nerves in the arms, and radiation to the groin may damage nerves in the legs. Weakness or loss of sensation may result.