What is a Neonatal Seizure?
A neonatal seizure occurs as the result of sustained, abnormal electrical discharge from brain cells (neurons) in a child during the first 28 days after birth. This abnormal discharge may be accompanied by behavioral changes in the baby, in which case the seizure is termed a clinical seizure. Behavioral changes can involve rhythmic twitching of one side of the face, an arm or a leg, which cannot be suppressed (ie does not stop when the limb is held or the baby is woken from sleep). Other behavioral changes may be more subtle and include breathing irregularity or brief cessation of breathing (apnea), sustained deviation of the eyes to one side, abnormal posturing of the arms or legs, quick jerks of the arms or legs, etc. At other times, babies can have seizures seen on an EEG (brain wave test) but can show no clinical changes of these – these are called subclinical or electrographic-only seizures.
Given their very young age, babies will often show unusual movements such as chewing, unusual posturing, quick jerks which are part of normal baby behavior and are not seizures. This makes accurate diagnosis of neonatal seizures based on observation of the infant alone is very difficult. An EEG is usually recommended (a) to confirm the behavioral events of concern are truly clinical seizures, and (b) to ensure the baby is not having subclinical seizures
How Common are Neonatal Seizures?
Seizures are the most common neurological problem seen in the neonatal period, affecting approximately 0.5% of term infants and 20% of preterm infants. The risk is highest in sick babies – particularly those who have neonatal encephalopathy (which may result from inadequate blood and oxygen to the baby just prior to birth or around the time of birth), brain infections (such as meningitis or encephalitis), bleeding or stroke, or babies who have congenital heart problems, particularly if they have required heart surgery.
What Causes Neonatal Seizures?
In the majority of neonates with seizures, an underlying cause for the seizures can be identified.
The most common etiology is neonatal encephalopathy, described above. In cases of neonatal encephalopathy, there usually were concerns regarding fetal heart rate during labor. Meconium is often present in the amniotic fluid before delivery. These infants usually have low Apgar scores and require extensive resuscitation at birth. However, many babies with these concerns identified do not go on to develop neonatal encephalopathy or seizures. Babies with neonatal encephalopathy are often excessive sleepy and less responsive for the first few days of life and may also show evidence of kidney (decreased urine production), liver (problems with blood clotting) or heart concerns (need for medications to support blood pressure), which resolve over the first few days. Seizures typically begin in the first 24-48 hours and often resolve by 72 hours of age.
Strokes are also common in the newborn period and result in blockage of blood flow to a blood vessel in the brain, and, while the exact cause is usually not known, it is assumed that these may result from small clots from the placenta. Infants with congenital heart disease are also at higher risk of stroke. Babies with strokes frequently have intermittent periods of focal twitching of the limb(s) of one side of the body only, and may show reduced use of the arm/leg that is involved in the seizure. A condition called sinovenous thrombosis is also common in neonates, and is due to clot formation in one of the large veins in the brain. This condition is more likely in babies of diabetic mothers, those with congenital heart problems, in the presence of dehydration or in babies with very high red blood cell counts (polycythemia).
Intracranial bleeding is also a common cause for seizures. Preterm infants are at higher risk for intraventricular hemorrhage (IVH) due to immaturity of blood vessels in this portion of the brain. This type of bleed involves hemorrhage into brain tissue just adjacent to the large fluid filled cavities in the brain (ventricles) or into those cavities. While IVH may be associated with seizures, it typically is not. Subarachnoid hemorrhage is not uncommon in term babies and involves bleeding into the cerebrospinal fluid that bathes the brain. Typically, term infants with subarachnoid hemorrhage appear well, other than for their seizures, which are usually self-limited. Occasionally babies may have subdural or intraparenchymal bleeding, and this type of bleeding is more common in the presence of a traumatic birth. Diagnosis of strokes or bleeds is made by neuroimaging, most commonly MRI of the brain.
Brain infections must also be considered, including meningitis or encephalitis. Bacterial meningitis may be transmitted to the infant through an infected mother or may be acquired after birth. A particular bacteria called Group B Strep is present in many asymptomatic women and can result in serious infection in the baby. Women who have cultured positive for Group B Strep are commonly given antibiotics during labor to reduce risk of transmission to their baby. Babies with brain infections usually present with excessive sleepiness, problems with temperature control (either fever or hypothermia) and may have feeding difficulties. Diagnosis is confirmed with spinal tap.
Metabolic problems may also cause seizures. Low blood glucose, or hypoglycemia, is a relatively common and very treatable cause of neonatal seizures. Babies of diabetic mothers, preterm infants and babies who are small for their gestational age are at particular risk of hypoglycemia. A bedside glucose should be checked in any newborn with new-onset seizures, and if low, glucose must be promptly administered. Other metabolic problems that result in seizures include low levels of calcium, high or low levels of sodium or inborn errors of metabolism. Inborn errors of metabolism result from an infant having a critically low level of a particular enzyme that is needed to metabolize a nutrient. Such disorders are more common in certain families (prior child with similar condition), and most commonly present after the 2-3rd day of life with worsening sedation, hiccups, unusual odor, and/or eye movement abnormalities, in addition to seizures. These disorders can be diagnosed through special blood and urine studies. Very rarely, deficiencies in specific vitamins (pyridoxine, pyridoxal-5-phosphate) can result in neonatal seizures.
Other very rare causes of neonatal seizures include brain malformations, drug withdrawal or intoxication and genetic causes (benign familial neonatal seizures). In this latter condition, a particular gene is associated with development of neonatal seizures which then remit spontaneously. There is usually a family history of other family members with neonatal seizures.
How are Neonatal Seizures Treated?
When treating newborn infants with seizures, it is important to address and treat the underlying cause of the seizures as well as administer an antiepileptic medication to stop the seizures. The most commonly used antiepileptic medication is phenobarbital. However, other options including lorazepam, diazepam, midazolam, fosphenytoin or levetiracetam have also been used. Seizures due to neonatal encephalopathy may be very difficult to control for the first 72 hours, but then often improve. In cases where seizures are very subtle, or subclinical only, EEG monitoring can be very helpful to confirm seizure control has been achieved.
In many neonates with seizures, antiepileptic medications can be stopped, sometimes prior to discharge from the Neonatal Intensive Care Unit, and sometimes after only several months of treatment. In most of these children, seizures will not recur.
What is the Outcome of Babies Who Have Had Neonatal Seizures?
One of the biggest predictors of outcome is the underlying cause of the seizures. Most babies who have only mild-moderate neonatal encephalopathy and babies with subarachnoid hemorrhage do well. The outcome in children with hypoglycemia or brain infections is more concerning, and depends on severity – however approximately half of these infants will do well. Babies who have severe neonatal encephalopathy, or those with an underlying brain malformation usually have long term neurological difficulties which may include ongoing epilepsy, motor problems such as cerebral palsy, and learning problems. The EEG pattern may help in predicting of outcome.
by Elaine Wirrell, MD
Mayo Clinic, Minnesota
Last Reviewed: 10/17/2012
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