Clinical Review

Cerebral palsy: A look at etiology and new task force conclusions

OBG Manag. 2003 May;15(5):40-50

An expert reviews new ACOG criteria on the link between hypoxic injury and cerebral palsy during childbirth and explores the unexpected role of technological advances.

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References

1. B-Lynch C, Coker A, Dua JA. A clinical analysis of 500 medico-legal claims evaluating the causes and assessing the potential benefit of alternative dispute resolution. Br J Obstet Gynaecol. 1996;103:1236-1242.

2. National Center on Birth Defects and Developmental Disabilities. Cerebral Palsy. Atlanta, Ga: Centers for Disease Control and Prevention; updated December 2002. Available at: www.cdc.gov/ncbddd/dd/ddcp.htm. Accessed March 21, 2003.

3. Fact Sheet: Cerebral Palsy. Washington, DC: National Information Center for Children and Youth with Disabilities; August 2002. Available at: www.nichcy.org/pubs/factshe/fs2.pdf. Accessed March 21, 2003.

4. Berger R, Garnier Y. Perinatal brain injury. J Perinat Med. 2000;28:261-285.

5. MacLennan A. A template for defining a causal relation between acute intrapartum events and cerebral palsy: international consensus statement. BMJ. 1999;319:1054-1059.

6. Dear P, Newell S. How much certainty is enough? BMJ. 2000;320:1075.-

7. Blumenthal I. Cerebral palsy—medicolegal aspects. J R Soc Med. 2001;94:624-627.

8. American College of Obstetricians and Gynecologists. Neonatal Encephalopathy and Cerebral Palsy: Defining the Pathogenesis and Pathophysiology. Washington, DC: ACOG; 2003.

9. Williams K, Hennessy E, Alberman B. Cerebral palsy: Effects of twinning, birthweight, and gestational age. Arch Dis Child. 1996;75:F178-F182.

10. Allen MC, Donohue PK, Dusman AE. The limit of viability—neonatal outcome of infants born at 22 to 25 weeks’ gestation. N Engl J Med. 1993;329:1597-1601.

11. Wood NS, Marlow N, Costeloe K, Gibson AT, Wilkinson AR. the EPICure Study Group. Neurologic and developmental disability after extremely preterm birth. N Engl J Med. 2000;343:378-384.

12. Hack M, Willson-Costello D, Friedman H, Taylor GH, Schluchter M, Fanaroff AA. Neurodevelopment and predictors of outcomes of children with birth weights of less than 1,000 g. Arch Pediatr Adolesc Med. 2000;154:725-731.

13. Vohr BR, Wright LL, Dusick AM, et al. Neurodevelopmental and functional outcomes of extremely low birth weight infants in the National Institute of Child Health and Human Development Neonatal Research Network, 1993-1994. Pediatrics. 2000;105:1216-1226.

14. Blickstein I. Cerebral palsy in multifetal pregnancies. Dev Med Child Neurol. 2002;44:352-355.

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20. Blickstein I. Cerebral palsy in multifetal pregnancies: Facts and hypotheses. In: Chervenak FA, Kurjak A, eds. Fetal Medicine: The Clinical Care of the Fetus as a Patient. London, England: Parthenon Publishing; 1999;368-373.

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KEY POINTS

Cerebral palsy occurs as a result of an intrapartum event in no more than 10% of cases.
Only cerebral palsy involving spastic quadriplegia is associated with an acute interruption of the blood supply, while purely dyskinetic or ataxic cerebral palsy generally is genetic in origin.
Epidemiologic studies have clearly demonstrated a causal relationship between premature birth and cerebral palsy.

Not only is cerebral palsy the most serious handicap of intrauterine and early neonatal life, it is the most common cause of medicolegal disputes in obstetrics.¹

Using findings from a 2003 task force, this article outlines current understanding of the causes of cerebral palsy, summarizes the updated criteria for determining whether it is the result of an intrapartum event, and assesses the association between cerebral palsy and various factors, including prematurity and multiple gestation.

Prevalence

Cerebral palsy is the most common developmental disability in the United States; roughly half a million Americans have some degree of the disorder. In a surveillance program initiated by the Centers for Disease Control and Prevention (CDC), the average annual prevalence rate was 2.8 per 1,000 children (ages 3 to 10, 1991-1994).² Annually, at least 8,000 cases are diagnosed in infants, while almost 1,500 are identified in children of preschool age.³

How hypoxemia leads to brain damage

Although the spectrum of current thought on cerebral palsy’s etiology is beyond the scope of this article, the subject has been explored extensively in recent years.⁴ We now know that no more than 10% of cases are the result of an intrapartum event.

Brain damage does appear to be the end result of a hypoxemic event. This event follows significant—usually abrupt—reduction in either the umbilical or uterine blood flow. Animal models demonstrate that even 12 hours of hypoxemia in midtrimester are sufficient to cause neuronal death.⁵ During the third trimester, fetal hypoxemia of moderate severity—sometimes encountered in cases with placental insufficiency—also can cause brain damage. When hypoxemia occurs immediately before or during labor, it is called a “sentinel” event, usually involving such entities as premature placental separation, uterine rupture, acute maternal hypotension, prolapsed umbilical cord, ruptured vasa previa, and tightened true knot of the umbilical cord.

If the sentinel event is severe enough, the fetus dies in utero. Otherwise, a series of reactions occurs:

Blood is redistributed to protect vital fetal organs such as the brain, heart, and adrenals. (This circulatory centralization is less feasible for preterm fetuses.)
The hypoxia- and acidosis-induced vasodilatation in the brain is followed by hypoperfusion, a process that is facilitated by oxygen radicals.
Finally, a reperfusion phase occurs, during which enzyme-mediated cellular damage is thought to result from a massive influx of calcium via damaged ion channels. At this phase, cellular injury is presumably caused by the inhibition of protein synthesis, the release of noxious agents, or by apoptosis. An intrauterine infection triggering the release of inflammatory agents may produce a similar effect.⁴

2003 task force redefines link between cerebral palsy and intrapartum event

It is seldom possible to determine the precise time brain damage occurs.⁵ This issue often arises during medicolegal proceedings, when the parties try to ascertain any cause-and-effect relationship between intrapartum events and cerebral palsy.^6,7

To address this question, in 1999 the International Cerebral Palsy Task Force—composed of obstetricians, neonatologists, child neurologists, and other clinical and scientific specialists—developed a set of criteria that defined when such a causal relationship existed.⁵ These criteria were updated earlier this year by the American College of Obstetricians and Gynecologists (ACOG) Task Force on Neonatal Encephalopathy and Cerebral Palsy, in conjunction with the American Academy of Pediatrics.⁸ The task force concluded that:

while neonatal encephalopathy does not always lead to permanent neurologic impairment, “the pathway from an intrapartum hypoxic-ischemic injury to subsequent cerebral palsy must progress through neonatal encephalopathy”;
only cerebral palsy involving spastic quadriplegia is associated with an acute interruption of the blood supply;
purely dyskinetic or ataxic cerebral palsy generally is genetic in origin; and
most importantly, “approximately 70% of neonatal encephalopathy is secondary to events arising before the onset of labor.”⁸

Both task forces provide sound arguments that cerebral palsy has many causes, including developmental and metabolic abnormalities, infection, and autoimmune and coagulation disorders, as well as trauma and hypoxia in the fetus-neonate. In the updated criteria, 4 essential conditions must be met in order to define an acute intrapartum event as sufficient to cause cerebral palsy (TABLE). The task force also detailed nonspecific criteria that collectively may suggest an intrapartum timing of hypoxic injury.

It is seldom possible to determine the precise time brain damage occurs—an issue that often arises during medicolegal proceedings.