Static Encephalopathy



Static Encephalopathy


Timothy E. Lotze



Static encephalopathy is a syndrome of abnormal motor functions and postural mechanisms caused by nonprogressive abnormalities of the developing brain. The term encompasses a heterogenous group of disorders whose causes are diverse, and it often is used synonymously with the term cerebral palsy (see Chapter 396). In addition to the motor dysfunction, which may range from mild to severe, associated neurologic difficulties, including mental retardation, seizures, communication dysfunction, and visual and hearing deficits, may be present. Furthermore, a variety of musculoskeletal problems may result. In the United States, as many as 500,000 children and adults may be affected. Thus, they represent an important public health responsibility.

The classification of static encephalopathy has changed little from Freud’s description of more than a century ago. These categories reflect the involvement, individually or in combination, of the following structures: the cerebral hemispheres, leading to upper motor neuron signs including hypertonia and spasticity; the basal ganglia, leading to extrapyramidal signs; and the cerebellum, leading to hypotonia and ataxia. The resulting classification includes spastic forms (hemiplegia, diplegia, or tetraplegia), extrapyramidal forms (choreoathetosis or dystonia), and a cerebellar form (ataxia). Frequently, the clinical picture is not pure, and mixed forms often are described. The comparative frequency of each form of static encephalopathy as determined from Swedish studies is shown in Table 398.1. The preponderance of spastic forms is evident. In general, male subjects outnumber female subjects at a ratio of 1.2:1.0. The increasing prominence of diplegic forms (symmetric lower extremity involvement greater than that in the upper extremities) is the result of increased survival of low-birth-weight infants (Table 398.2).

The prevalence of static encephalopathy has changed substantially since 1960. During the 1960s, a decline in the prevalence of static encephalopathy to 1.5 per 1,000 live births was attributed to improved prenatal and perinatal care. In particular, better treatment of Rh incompatibility, with resulting decrease in damage to basal ganglia from kernicterus, has led to a reduction of the extrapyramidal form. Conversely, through the 1970s, the prevalence steadily increased, related to better perinatal care, especially of very low-birth-weight infants. The current overall prevalence of static encephalopathy is 2.1 per 1,000 live births, and this rate has not changed significantly during the past 3 decades. For the most recent reporting period from the Swedish population-based studies, gestation-related prevalences were 86 per 1,000 live births for extremely premature infants of less than 28 weeks’ gestation, 60 per 1,000 for infants of 29 to 31 weeks’ gestation, 6 per 1,000 for those of 32 to 36 weeks’ gestation, and 1.3 per 1,000 for infants of more than 36 weeks’ gestation. Overall, nearly 50% of affected children were low-birth-weight infants (i.e., less than 2,500 grams). A slight increase in the prevalence for static encephalopathy among infants of less than 31 weeks’ gestation occurred for this period. This increase has been attributed in part to the rise in multiple births owing to more frequent use of assisted fertilization.








TABLE 398.1. COMPARATIVE PERCENTAGE DISTRIBUTION OF STATIC ENCEPHALOPATHY (SWEDISH SERIES, 1991 TO 1994)

















Hemiplegia 33%
Tetraplegia 6%
Diplegia 44%
Ataxia 4%
Dyskinesia 12%


RISK FACTORS

Risk factors for static encephalopathy vary with the period or timing of the insult. More than a century ago, Little described static encephalopathy and related it causally to difficulties in the birth process. However, data from several large population-based studies confirmed the subsequent theory, first advanced by Freud, that static encephalopathy in most children cannot be attributed to birth asphyxia and that “difficult birth in itself is merely a symptom of deeper effects that influenced the development of the fetus.” Intrapartum asphyxia is thought to be causely related in only 20% of cases of static encephalopathy. Congenital disorders may account for 30% to 40% of the total, and infections of the central nervous system account for another 5% to 10%. In fact, no specific cause can be identified for as many as 50% of infants in whom the condition develops. In infants born at term, neonatal events that previously have been attributed to asphyxia are at least as likely to occur in association with underlying congenital disease. These events include meconium in the amniotic fluid, low 10-minute Apgar scores, neonatal seizures, apnea, newborn neurologic abnormalities, and slow head growth. The term infant with low Apgar scores from a late asphyxial event who does not show signs of newborn encephalopathy will not develop static encephalopathy. Furthermore, epilepsy and mental retardation alone do not follow birth asphyxia as the sole cause. Prematurity, low birth weight, and placental dysfunction are increasingly important factors in the genesis of static encephalopathy. Risk factors in the very low-birth-weight infant include hypotension, acidosis, sepsis, seizures, pneumothorax, and prolonged ventilation.

Spastic diplegia most commonly is the result of prematurity and postnatal complications of premature birth, including periventricular leukomalacia and intraventricular hemorrhage. When it occurs in the full-term infant, spastic diplegia usually is the result of a complicated pregnancy and delivery. Spastic diplegia does not occur in the term infant whose only insult at birth is late asphyxia (i.e., antenatal risk factors must be considered).

Since 1960, infant mortality has decreased dramatically in the developed countries of the world. This decrease has been attributed to improved prenatal and perinatal care. That these improvements have not had a favorable effect on the frequency of static encephalopathy provides further support for causative factors other than the birth process itself in this disorder.
Extensive evaluation of electronic fetal monitoring revealed that this technique did not improve the outcome in terms of neurologic development in either term or preterm infants.








TABLE 398.2. COMPARATIVE GESTATIONAL PERCENTAGE DISTRIBUTION OF STATIC ENCEPHALOPATHY (SWEDEN, 1991 TO 1994)




















Type <28 Weeks 29–31 Weeks 32–36 Weeks >36 Weeks
Hemiplegia 9% 10% 32% 44%
Diplegia 83% 76% 56% 25%

To define a causal relationship between intrapartum events and cerebral palsy more clearly, the International Cerebral Palsy Task Force developed a set of specific criteria that were refined further in 2003. These criteria are described in Box 398.1. Additionally, the investigators concluded that only cerebral palsy involving spastic quadriplegia is associated with significant intrapartum events and that purely dyskinetic or ataxic forms generally are genetic in origin. Infants injured during the prenatal period may have had time to recover before parturition and thus may not have perinatal encephalopathy. Their static problems can be assigned clearly to insults occurring at a time other than birth.

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Jul 24, 2016 | Posted by in ORTHOPEDIC | Comments Off on Static Encephalopathy
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