129: Seizures

I. DEFINITION

A seizure is defined clinically as a paroxysmal alteration in neurologic function (ie, behavioral, motor, or autonomic function).

II. INCIDENCE

Neonatal seizures are relatively common and occur in 0.15–1.5% of all neonates.

III. PATHOPHYSIOLOGY

The neurons within the central nervous system (CNS) undergo depolarization as a result of inward migration of sodium. Repolarization occurs via efflux of potassium. A seizure occurs when there is excessive depolarization, resulting in excessive synchronous electrical discharge. Volpe (2001) proposed the following 4 possible reasons for excessive depolarization: failure of the sodium-potassium pump because of a disturbance in energy production, a relative excess of excitatory versus inhibitory neurotransmitter, a relative deficiency of inhibitory versus excitatory neurotransmitter, and alteration in the neuronal membrane, causing inhibition of sodium movement. The basic mechanisms of neonatal seizures, however, are unknown.

IV. ETIOLOGY

There are numerous causes of neonatal seizures, but relatively few account for most cases (Table 129–1). Therefore, only common causes of seizures are discussed here.

1. Perinatal asphyxia is the most common cause of neonatal seizures. These occur within the first 24 hours of life in most cases and may progress to overt status epilepticus. In premature infants, seizures are of the generalized tonic type, whereas in full-term infants they are of the multifocal clonic type. Accompanying subtle seizures are usually present in both types.

2. Intracranial hemorrhage, whether subarachnoid, periventricular, or intraventricular, may occur as a result of hypoxic insults that can lead to neonatal seizures. Subdural hemorrhage, usually a result of trauma, can cause seizures.

   1. In primary subarachnoid hemorrhage, convulsions often occur on the second postnatal day, and the infant appears quite well during the interictal period.

   2. Periventricular or intraventricular hemorrhage arising from the subependymal germinal matrix is accompanied by subtle seizures, decerebrate posturing, or generalized tonic seizures, depending on the severity of the hemorrhage.

   3. Subdural hemorrhage over the cerebral convexities leads to focal seizures and focal cerebral signs.

3. Metabolic disturbances

   1. Hypoglycemia is frequently seen in infants with intrauterine growth retardation and in infants of diabetic mothers (IDMs). The duration of hypoglycemia and the time lapse before initiation of treatment determine the occurrence of seizures. Seizures are less frequent in IDMs, perhaps because ...