Physical injury—for example, sports or car accidents—poisoning, infection, blocked blood vessels, and tumors can all cause paralysis. in the developing brain of the fetus or brain injury during birth can cause a paralytic condition known as cerebral palsy. In diseases such as multiple sclerosis, inflammation scars the nerves, interrupting communication between the brain and the muscles. Sometimes the muscle tissue itself is affected. In muscular dystrophy, deterioration of the muscle tissue of the arms and legs causes increasing weakness.
Guillain-Barre (gee-YAN ba-RAY) syndrome is an autoimmune disorder in which the body's own cells attack the insulation and core of the nerve fibers, beginning in the hands and feet. In myasthenia gravis (my-es-THEE-nee-a GRA-vis), another autoimmune disorder, a chemical malfunction disrupts the communication needed for muscles to contract.
In rare cases, no physical cause for paralysis can be found. Psychologists call this condition a conversion disorder—that is, a person converts his or her psychological anxiety into physical symptoms of paralysis, but nerve and muscle function are still intact.