A set of clinical features may be stereotyped enough to warrant classification as a syndrome even though cases are not common. One such syndrome, involving generalized seizures in very young infants, is known as benign familial neonatal seizures.
The diagnosis of this syndrome in a child with seizures is based on five criteria:
- normal neurologic examination
- negative evaluation for another etiology of the seizures
- normal developmental and intellectual outcome
- positive family history of newborn or infantile seizures with benign outcome
- onset of seizures during the neonatal or early infantile period) 25
Early reports indicated that the seizures began during the first week of life, usually on the third day. More recently, the onset in some patients has been noted to be after the first week. Whether these infants should be considered to have a distinct syndrome is not yet settled.
The seizures usually occur frequently for a few days and then stop. The infant is usually alert and vigorous during the interictal period.
Clonic seizures, which may appear to be focal or multifocal, are the most frequent type, although generalized seizures have also been reported. The seizures are generally brief, lasting for approximately 1 to 2 minutes, but may occur as many as 20 to 30 times a day.
Linkage analysis in large families of patients with benign neonatal convulsions have demonstrated two loci for the disorder, located on chromosomes 20q13.3 and 8q24. The genes encode voltage-gated K+ channels expressed in the brain (KCNQ2 and KCNQ3).25
The EEG is of little assistance in making the diagnosis of benign familial neonatal seizures. It may or may not be abnormal interictally, and no diagnostic features have been described. Abnormalities reported have included spikes, sharp waves, "epileptiform" patterns, "generalized periodicity," and slowing. Abnormal findings are frequently transient, however.
In many published case reports, electroencephalography was not performed or the results were not described in sufficient detail.
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)