It is sometimes said by adult practitioners that children are just small adults. Child neurologists recognize that adults are just large children, albeit with lesser potential. The knowledge of nervous system anatomy and physiology that is essential to accurate localization and diagnosis in adults must be complemented by a thorough understanding of the sequence and variability of normal development to attain the same goals in children. The challenge and promise of child neurology is that children have extraordinary potential for recovery and development in the face of insults that would devastate adults. They are subject to all of the groups of diseases that occur in adults, as well as many others that are unique to the developing brain. This chapter focuses on the essentials of the most prominent of these age-related encephalopathies.
NEONATAL NEUROLOGIC DISORDERS
Hypoxic-ischemic encephalopathy (HIE) can be the result of birth asphyxia or at-risk pregnancies, in which the fetus has prenatal problems that are independent of the delivery process. The term neonatal encephalopathy is preferred when infant depression at birth is not tied to a hypoxic ischemic insult (eg, infection). HIE guidelines include profound metabolic or mixed acidemia (pH <7), persistent Apgar score of 0–3 for longer than 5 minutes, multiple organ involvement (eg, kidney, lungs, liver, heart, intestines) and neurologic findings (see below). Clinical examination and neuroimaging are the most significant predictors of central nervous system (CNS) damage.
Clinical manifestations of HIE differ between term and preterm infants. In term infants, three grades are identified: (1) mild, present in the first 24 hours and characterized by a hypervigilant jittery state; (2) moderate, characterized by lethargy or depressed sensorium and decreased spontaneous movements during the initial 24 hours (the infant is jittery when aroused); and (3) severe, characterized by obtundation or coma, seizures, hypotonia, absent reflexes, and depressed sucking and swallowing. The clinical expression of HIE is muted in preterm infants.
Lactic acidemia (pH <7.0) is usually seen at the time of birth. HIE is often associated with hypoxic damage to other systems (eg, renal shutdown or necrotizing enterocolitis).
Neuroimaging may show diffuse or focal ischemia (cortical or subcortical). Brief transient ischemia that does not reach criterion for HIE encephalopathy may result in infarction of the basal ganglia that clinically can result in the choreoathetoid form of cerebral palsy or of purkinje cells that result in ataxia.
Electroencephalography is helpful in term infants in determining outcome: infants with normal electroencephalograms (EEGs) have a favorable prognosis; those with EEGs showing depressed background or burst-suppression patterns have an unfavorable one.
The main differential diagnosis of HIE is neonatal sepsis, which should be suspected in all infants with presumptive HIE until proven otherwise. The placenta should be examined for signs of chorioamnionitis.