Chapter 120: Seizures

I. DEFINITION

A seizure is defined clinically as a paroxysmal alteration in neurologic function (ie, behavioral, motor, or autonomic function). (See also Chapter 82 for on-call management of seizures).

II. INCIDENCE

Neonatal seizures are relatively common and occur in 2 to 3 neonates per 1000 births of all neonates; the incidence is more common in premature infants, with an occurrence in up to 130 per 1000.

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 neurotransmitters, a relative deficiency of inhibitory versus excitatory neurotransmitters, 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. Therefore, only common causes of seizures are discussed here. See Table 120–1 for a more extensive list of causes.

1. Perinatal asphyxia is the most common cause of neonatal seizures. Hypoxic ischemic encephalopathy (HIE) is seen in approximately 1 to 2 per 1000 live births. In fact, about two-thirds of cases of neonatal seizures are due to HIE. These occur within the first 24 hours of life in most cases. 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

   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 in preterm neonates 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. It is usually secondary to trauma.

3. Metabolic disturbances

   1. Hypoglycemia is frequently seen in infants with intrauterine growth retardation and in infants of diabetic mothers. The duration of hypoglycemia and the time lapse before initiation of treatment determine the occurrence of seizures.

   2. Hypocalcemia has been noted in low birthweight infants, infants of diabetic mothers, asphyxiated infants, infants with DiGeorge syndrome, and infants born to mothers with hyperparathyroidism. Hypomagnesemia is a frequent accompanying problem.

   3. Hyponatremia occurs because of improper fluid management or as a result of the syndrome of inappropriate antidiuretic hormone.

   4. Hypernatremia is seen with dehydration as a result of inadequate intake in breast-fed infants or incorrect dilution of concentrated formula.

   5. Other metabolic disorders

      1. Pyridoxine dependency. Leads ...