A set of clinical features may be stereotyped enough to warrant classification as a syndrome even though cases are not common. One pattern of seizures in very young infants is known as benign neonatal convulsions or benign neonatal idiopathic seizures. These seizures occur in otherwise healthy, full-term infants.26,27,29,30

Criteria used to make the diagnosis include:27-29,31

  1. birth after 39 weeks of gestation
  2. an APGAR score of 9 or above 5 minutes after birth
  3. the presence of a seizure-free interval between birth and the onset of seizures
  4. clonic or apneic seizures, or both
  5. negative evaluations for etiology
  6. a favorable outcome in regard to neurologic development
  7. lack of seizures outside the neonatal period

Typically the seizures begin on the fifth day of life. Some authors have used the term "fifth-day fits."27 Benign idiopathic neonatal seizures and fifth-day fits appear to be identical syndromes. In a review of six different series of patients with benign idiopathic neonatal seizures, Plouin27 noted that in all 182 patients described, the onset of seizures occurred between the first and seventh day of life. In 80% of these infants, the initial seizure occurred on the fourth, fifth, or sixth day of life. The first seizure occurred on day 5 in half of the cases for which the exact day was reported.

The seizures are usually partial clonic and may be confined to one body part or migrate from one region to another. Apnea may occur with the clonic activity or be the sole manifestation of the seizure. Tonic seizures are rare.

The seizures often occur in a crescendo of activity. Initially the infant is normal between seizures. The seizures then increase in frequency until the child goes into status epilepticus. The flurry of seizures usually lasts less than 24 hours but may continue for a few days.27,29

Electroencephalography

EEG findings in benign idiopathic neonatal seizures vary. In a survey of 101 EEGs from infants with the disorder,27 the interictal EEG:

  • was normal in 10 infants
  • was excessively discontinuous in 6
  • showed "focal or multifocal" abnormalities in 25
  • showed the theta pointu alternant pattern in 60

The theta pointu alternant pattern consists of dominant theta activity that is discontinuous, unreactive, often asynchronous, and has intermixed sharp waves. It is present throughout sleep and the awake state and may persist up to the 12th day of life, even after the seizures have ceased.

The theta pointu alternant pattern is not specific for benign seizures and can be seen after a variety of neonatal encephalopathies. However, Plouin27 claims that this EEG pattern is associated with a favorable prognosis regardless of etiology.

Adapted from: Holmes GL. Classification of seizures and the epilepsies. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 1-36.
With permission from Elsevier (www.elsevier.com)

Authored by: Gregory L. Holmes | MD on 1/2004
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