Causes
In recent
years there has been a slight increase in the proportion of children
who have cp; currently about one in every 400 is affected. Among
these, the percentage of severely and multiply disabled people
needing social support is growing. That need will continue
throughout their lives.
We do not
know the cause of most cases of cerebral palsy. That is, we are
unable to determine what caused cerebral palsy in most children who
have congenital CP. We do know that the child who is at highest risk
for developing CP is the premature, very small baby who does not cry
in the first five minutes after delivery, who needs to be on a
ventilator for over four weeks, and who has bleeding in his brain.
Babies who have congenital malformations in systems such as the
heart, kidneys, or spine are also more likely to develop CP,
probably because they also have malformations in the brain. Seizures
in a newborn also increase the risk of CP. There is no combination
of factors which always results in an abnormally functioning
individual. That is, even the small premature infant has a better
than 90 percent chance of not having cerebral palsy. There are a
surprising number of babies who have very stormy courses in the
newborn period and go on to do very well. In contrast, some infants
who have rather benign beginnings are eventually found to have
severe mental retardation or learning disabilities.
The
causes of cerebral palsy 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, infections
during infancy and early childhood, eg meningitis or encephalitis,
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
microorganisms 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.
Many
children with cerebral palsy have a congenital malformation of the
brain, meaning that the malformation existed at birth and was not
caused by factors occurring during the birthing process. Not all of
these malformations can be seen by the physician, even with today's
most sophisticated scans, but when CP is recognized in a newborn, a
congenital malformation is suspected. When a diagnosis of CP is
made, the mother and father often feel guilty and wonder what they
did to cause their child to have this disorder. While it is
certainly true that good prenatal care is an essential part of
preventing congenital problems, it must be stated that congenital
problems, or "birth defects," often occur even when the mother has
strictly followed her physician's advice in caring for herself and
the developing infant. Though the causes of "birth defects" are
usually unknown, we do know that the developing brain can be
affected by several factors. When the fetus is exposed to certain
chemicals or infections through the expectant mother, for example.
The developing brain can be injured if the expectant mother suffers
severe physical trauma, the fetal brain can be injured, too, but
this is rare. Finally, prematurity and a low birth weight have been
shown to be related to an increased incidence of specific disorders.
Many chemicals are known to adversely affect the developing brain,
alcohol being the most commonly used. The term Fetal Alcohol
Syndrome describes the long-term, multi-system effect of alcohol on
a child whose mother abused alcohol during the pregnancy. When a
fetus is exposed to large amounts of alcohol, several body systems,
including the neurological system will almost certainly suffer
damage. Cigarette smoking by the mother has been shown to decrease
birth weight, and low birth weight is associated with several
disorders, including cerebral palsy.
Severe
malnutrition in the mother can adversely affect brain growth in the
fetus, and it, too, can result in a low birth weight. The use of
cocaine or crack by the expectant mother is associated with blood
vessel complications, and these complications affect many organs as
well as the central nervous system. Cocaine use is increasing and
thus becoming more prevalent as cause of brain damage in infants.
Most infants whose mothers used cocaine during pregnancy develop
mental retardation rather than cerebral palsy, however. Infections
such as rubella (German measles), toxoplasmosis, and cytomegalovirus
(CMV), ( if a woman has them during pregnancy), also may injure the
brain of the fetus. Rubella can be prevented by immunization, prior
to becoming pregnant, and the chances of becoming infected with
toxoplasmosis can be minimized by not handling the feces of cats and
by avoiding raw or uncooked meat.
Congenital infection with human immunodeficiency virus (HIV, the
virus that causes AIDS) also causes brain damage in children, though
it usually causes mental retardation rather than CP. It is likely
that many other infections in the expectant mother injure the
developing fetus, but they are not recognized as causative factors
because the woman who has the infection either does not recognize
the symptoms of infection or is symptom-free. Premature infants are
at a much higher risk for developing cerebral palsy than full-term
babies, and the risk increases as the birth weight decreases.
Between 5 and 8 percent of infants weighing less than 1500 grams (3
pounds) at birth develop cerebral palsy, and infants weighing less
than 1500 grams are 25 times more likely to develop cerebral palsy
than infants who are born at full term weighing more than 2500
grams. Any premature infants suffer bleeding within the brain,
called intraventricular hemorrhages, intracranial hemorrhages.
Again, the highest frequency of hemorrhages is found in the babies
with the lowest weight: the problem is rare in babies who weigh more
than 2000 grams (4 pounds). This bleeding may damage the part of the
brain that controls motor function and thereby lead to cerebral
palsy. If the hemorrhage results in destruction of normal brain
tissue (a condition called periventricular leukomalacia) and small
cysts around the ventricles and in the motor region of the brain,
then that infant is more likely to have CP than an infant with
hemorrhages alone.
The most
important thing to remember is that you do not "catch" CP from
another person, and you do not develop CP later in life. It is
caused by an injury to the brain near the time of birth.
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