The neonatologist is often confronted by an infant who begins to convulse in the first days of life. In most instances, the seizures are fragmentary—an abrupt movement or posturing of a limb, stiffening of the body, rolling up of the eyes, a pause in respirations, lip-smacking, chewing, or bicycling movements of the legs. Even the experienced observer may have difficulty at times in distinguishing seizure activity from the normal movements of the neonate. If manifest seizures are frequent and stereotyped, the diagnosis is less difficult. The seizures correlate with focal or multifocal cortical discharges; however, as is the case with most EEG changes in neonates, these are poorly formed and less distinct than seizure discharges in later life. Presumably the immaturity of the cerebrum prevents the development of a fully organized seizure pattern, and the incomplete corticocortical myelination prevents bihemispheric spread. The EEG is nonetheless helpful in diagnosis. For example, periods of EEG suppression may alternate with sharp or slow waves, or there may be discontinuous theta activity that represents electrographic seizure activity. Conversely, electrical seizure activity in the neonate may be unattended by clinical manifestations.
An early onset of myoclonic jerks, either fragmentary or massive, with an EEG pattern of alternating suppression and complex bursts of activity is particularly ominous. Ohtahara described another unfavorable form of neonatal seizure evolving in infancy into infantile spasms (West syndrome) and Lennox-Gastaut syndrome and leaving in its wake severe brain damage. Most reported patients have been left developmentally delayed.
Neonatal seizures occurring within 24 to 48 h of a difficult birth are usually indicative of severe cerebral damage, usually anoxic, either antenatal or parturitional. Such infants often succumb, and about half of the survivors are seriously handicapped. Seizures having their onset several days or weeks after birth are more often an expression of acquired or hereditary metabolic disease. In the latter group, hypoglycemia is the most frequent cause; another, hypocalcemia with tetany, has become infrequent. A hereditary form of pyridoxine deficiency is a rare but treatable cause, sometimes also inducing seizures in utero and characteristically responding promptly to massive doses (100 mg) of vitamin B6 given intravenously. Biotinidase deficiency is another rare but correctable cause. Nonketotic hyperglycemia, maple syrup urine disease, as well as other metabolic disorders may lead to seizures in the first week or two of life and are expressive of a more diffuse encephalopathy.
In contrast, benign forms of neonatal seizures have also been identified. For example, Plouin described a form of benign neonatal clonic convulsions beginning on days 2 and 3, up to day 7, (“fifth day seizures”) in which there were no specific EEG changes. The seizures then remit and have a good prognosis. The inheritance is autosomal dominant. There are other nonfamilial cases with onset on days 4 to 6, wherein the partial seizures may even increase to status epilepticus; the EEG consists of discontinuous theta activity. In both these groups, the outlook for normal development is good and seizures seldom recur later in life. There are also benign forms of polymyoclonus without seizures or EEG abnormality in this age period. Some occur only with slow-wave sleep or feeding. They disappear after a few months and require no treatment. A form of benign nocturnal myoclonus in the neonate is also well known.