What causes cerebral palsy?
Cerebral palsy is caused by damage to the motor control centers of the brain. Many different types of injury to the brain can cause cerebral palsy, and most often a specific cause cannot be identified. Birth injuries and poor oxygen supply to the brain before, during, and immediately after birth cause 10 to 15% of cases. Prenatal infections, such as rubella, toxoplasmosis, or cytomegalovirus infection, sometimes result in cerebral palsy. Premature infants are particularly vulnerable, possibly in part because the blood vessels of the brain are poorly developed and bleed easily. High levels of
bilirubin in the blood can lead to a form of brain damage called kernicterus. During the first years of life, severe illness, such as inflammation of the tissues covering the brain (meningitis), sepsis, trauma, and severe dehydration, can cause brain injury and result in cerebral palsy.
Since cerebral palsy refers to a group of disorders, there is no exact known cause. Some major causes are asphyxia or hypoxia of brain, birth trauma or premature birth, genetic susceptibility, certain drugs or infections in the mother during and before birth, central nervous system infections, trauma, and consecutive hematomas. After birth, the condition may be caused by toxins, physical brain injury, incidents involving hypoxia to the brain (such as drowning), and encephalitis or meningitis. Despite all of these causes, the cause of many individual cases of cerebral palsy is unknown.
Cerebral palsy is most commonly the result of failure of a part of the brain to develop, either before birth or in early childhood. When the nerve cells (neurons) in these regions die, the appropriate signals can no longer be sent to the muscles under their control. The resulting poor control of these muscles causes the symptoms of CP. This brain damage may be caused by lack of oxygen (asphyxia), infection, trauma, malnutrition, drugs or other chemicals, or hemorrhage. In most cases it is impossible to determine the actual cause, although prematurity is recognized as a significant risk factor. Although it was once thought that difficult or prolonged delivery was responsible for many cases of CP, most researchers now believe that the great majority of cases result from brain damage occurring before birth. The same injury that damages the motor areas can harm other areas as well, leading to other problems commonly associated with CP. If brain cells do not get enough oxygen because of poor circulation, they may die. Defects in circulation in the developing brain may cause CP in some cases. Asphyxia during birth is also possible, and about half of newborns known to have suffered asphyxia during birth (perinatal asphyxia) develop CP. However, asphyxia during birth is usually considered a symptom of an underlying neurological problem in a newborn, rather than its cause, and the resulting CP may be another sign of that problem. Asphyxia after birth can be caused by choking, poisoning (such as from carbon monoxide or barbiturates), or near-drowning. The fetal brain may be damaged by an infection contracted by the mother. Infections correlated with CP include rubella (German measles), toxoplasmosis (often contracted from cat feces or undercooked meat), cytomegalovirus (a herpes virus), and HIV (the virus that causes AIDS). Encephalitis and meningitis, infections of the brain and its coverings, can also cause CP when contracted by infants.
The causes of cerebral palsy also include illness during pregnancy, premature delivery, or lack of oxygen supply to the baby; or it may occur early in life as a result of an accident, lead poisoning, viral infection, child abuse, or other factors. Chief among the causes is an insufficient amount of oxygen or poor flow of blood reaching the fetal or newborn brain. This can be caused by premature separation of the placenta, an awkward birth position, labor that goes on too long or is too abrupt, or interference with the umbilical cord. Other causes may be associated with premature birth, RH or A-B-O blood type incompatibility between parents, infection of the mother with German measles or other viral diseases in early pregnancy, and micro-organisms that attack the newborn's central nervous system. Lack of good prenatal care may also be a factor. A less common type is acquired cerebral palsy: head injury is the most frequent cause, usually the result of motor vehicle accidents, falls, or child abuse.