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What Causes Cerebral Palsy?
Cerebral palsy is not one disease with a single cause, like chicken pox or measles. It is a group of disorders with similar problems in control of movement, but probably with different causes. When physicians try to uncover the cause of cerebral palsy in an individual child, they look at the form of cerebral palsy, the mother's and child's medical history and onset of the disorder.
In the United States, about 10 percent to 20 percent of children who have cerebral palsy acquire the disorder after birth. (The figures are higher in underdeveloped countries.) Acquired cerebral palsy results from brain damage in the first few months or years of life and can follow brain infections, such as bacterial meningitis or viral encephalitis, or results from head injury — most often from a motor vehicle accident, a fall or child abuse.
Congenital cerebral palsy, on the other hand, is present at birth, although it may not be detected for months. In most cases, the cause of congenital cerebral palsy is unknown. Thanks to research, however, scientists have pinpointed some specific events during pregnancy or around the time of birth that can damage motor centers in the developing brain. Some of these causes of congenital cerebral palsy include:
· Infections during pregnancy. German measles, or rubella, is caused by a virus that can infect pregnant women and, therefore, the fetus, causing damage to the developing nervous system. Other infections that can cause brain injury in the developing fetus include cytomegalovirus and toxoplasmosis. There is relatively recent evidence that placental and perhaps other maternal infection can be associated with cerebral palsy.
· Jaundice in the infant. Bile pigments, compounds that are normally found in small amounts in the bloodstream, are produced when blood cells are destroyed. When many blood cells are destroyed in a short time, as in the condition called Rh incompatibility, the yellow-colored pigments can build up and cause jaundice. Severe, untreated jaundice can damage brain cells.
· Severe oxygen shortage in the brain or trauma to the head during labor and delivery. The newborn infant's blood is specially equipped to compensate for low levels of oxygen, and asphyxia (lack of oxygen caused by interruption in breathing or poor oxygen supply) is common in babies during the stresses of labor and delivery. But if asphyxia severely lowers the supply of oxygen to the infant's brain for lengthy periods, the child may develop brain damage called hypoxic-ischemic encephalopathy. A significant proportion of babies with this type of brain damage die, and others may develop cerebral palsy, which is then often accompanied by mental impairment and seizures.
In the past, physicians and scientists attributed most cases of cerebral palsy to asphyxia or other complications during birth if they could not identify another cause. However, extensive research by NINDS scientists and others has shown that very few babies who experience asphyxia during birth develop encephalopathy soon after birth. Research also shows that a large proportion of babies who experience asphyxia do not grow up to have cerebral palsy or other neurological disorders. Birth complications including asphyxia are now estimated to account for about 6 percent of congenital cerebral palsy cases.
· Stroke. Coagulation disorders in mothers or infants can produce stroke in the fetus or newborn baby. Bleeding in the brain has several causes — including broken blood vessels in the brain, clogged blood vessels or abnormal blood cells — and is one form of stroke. Although strokes are better known for their effects on older adults, they can also occur in the fetus during pregnancy or the newborn around the time of birth, damaging brain tissue and causing neurological problems. Ongoing research is testing potential treatments that may one day help prevent stroke in fetuses and newborns.
What are the Risk Factors?
Research scientists have examined thousands of expectant mothers, followed them through childbirth and monitored their children's early neurological development. As a result, they have uncovered certain characteristics, called risk factors, that increase the possibility that a child will later be diagnosed with cerebral palsy:
· Breech presentation. Babies with cerebral palsy are more likely to present feet first, instead of head first, at the beginning of labor.
· Complicated labor and delivery. Vascular or respiratory problems of the baby during labor and delivery may sometimes be the first sign that a baby has suffered brain damage or that a baby's brain has not developed normally. Such complications can cause permanent brain damage.
· Low Apgar score. The Apgar score (named for anesthesiologist Virginia Apgar) is a numbered rating that reflects a newborn's condition. To determine an Apgar score, doctors periodically check the baby's heart rate, breathing, muscle tone, reflexes and skin color in the first minutes after birth. They then assign points; the higher the score, the more normal the baby's condition. A low score at 10 to 20 minutes after delivery is often considered an important sign of potential problems.
· Low birthweight and premature birth. The risk of cerebral palsy is higher among babies who weigh less than 2,500 grams (5 lbs., 7 1/2 oz.) at birth and among babies who are born less than 37 weeks into pregnancy. This risk increases as birthweight falls.
· Multiple births. Twins, triplets and other multiple births are linked to an increased risk of cerebral palsy.
· Nervous system malformations. Some babies born with cerebral palsy have visible signs of nervous system malformation, such as an abnormally small head (microcephaly). This suggests that problems occurred in the development of the nervous system while the baby was in the womb.
· Maternal bleeding or severe proteinuria late in pregnancy. Vaginal bleeding during the sixth to ninth months of pregnancy and severe proteinuria (the presence of excess proteins in the urine) are linked to a higher risk of having a baby with cerebral palsy.
· Maternal hyperthyroidism, mental retardation or seizures. Mothers with any of these conditions are slightly more likely to have a child with cerebral palsy.
· Seizures in the newborn. An infant who has seizures faces a higher risk of being diagnosed, later in childhood, with cerebral palsy.
Knowing these warning signs helps doctors keep a close eye on children who face a higher risk for long-term problems in the nervous system. However, parents should not become too alarmed if their child has one or more of these factors. Most such children do not have and do not develop cerebral palsy.