Chapter 18 - Diagnosis of seizures and encephalopathy using conventional EEG and amplitude integrated EEG
Introduction
Monitoring the brain of the sick newborn infant in the NICU using either conventional electroencephalography (cEEG) or amplitude integrated EEG (aEEG) is essential in order to accurately detect seizures and assess the severity of neonatal encephalopathy (NE).
Seizures are more likely to occur in the neonatal period than at any other time in childhood (Silverstein, 2009), partly due to the susceptibility and relative hyperexcitability of the newborn brain. Intense synaptic formation in the neonatal period, overexpression of excitatory receptors, and the excitatory role of GABA up to term age all contribute to the increase in seizure frequency seen in this age group (Jensen, 2009). Seizures are a medical emergency and both animal (Wirrell et al., 2001) and human studies (Miller et al., 2002; Glass et al., 2009; Kharoshankaya et al., 2016) increasingly suggest that they may exacerbate neuronal damage beyond that caused by the underlying etiology alone.
Urgent detection is paramount and prompt treatment of seizures has been shown to reduce seizure burden (Srinivasakumar et al., 2015) with the potential to improve outcome.
Encephalopathy in the neonatal period is characterised by an altered mental status that can range anywhere from irritability to coma; seizures are common and other problems such as hypotonia, apnea, and feeding difficulties may be present, depending on the severity of the encephalopathy. The most common cause of NE is hypoxia–ischemia and it is therefore very common to see the term hypoxic–ischemic encephalopathy (HIE) used in the literature. However, the cause of an encephalopathy in the first hours and days after birth may not always be apparent and, as a result, many now prefer to use the term neonatal encephalopathy (Dammann et al., 2011; Volpe, 2012). Other causes of encephalopathy include stroke, hemorrhage, meningitis, structural brain abnormalities, inborn errors of metabolism, epileptic encephalopathy, vitamin responsive seizures, and nonaccidental injury (Martinello et al., 2017).
Confirmation of encephalopathy with EEG monitoring can act as an important adjunct to other investigations and the clinical examination, particularly when considering treatment strategies such as therapeutic hypothermia (TH) for HIE (Weeke et al., 2017b). Assessment of both cEEG and aEEG in infants with NE can offer valuable information regarding prognosis (Thoresen et al., 2010; Azzopardi, 2014; Weeke et al., 2016).
The more recent use of machine learning for the development of algorithms to continuously monitor the neonatal EEG, detect seizures (Temko and Lightbody, 2016), and grade encephalopathy (Stevenson et al., 2013) offers the exciting prospect of real-time decision support in the NICU in the very near future.
Section snippets
The Neonatal EEG: What Does It Measure?
The signals measured by the EEG are on the order of microvolts (μV) and represent summated postsynaptic neuronal activity in the cortex. EEG has a temporal resolution that is much higher than functional MRI and it can display brain activity on a millisecond scale. EEG also exhibits a rich variety of frequencies, amplitudes, and waveform morphologies from all monitored brain regions and features such as synchrony and symmetry across both cerebral hemispheres are very easily measured. A knowledge
aEEG and cEEG Monitoring in the NICU
Multichannel EEG with video is the gold standard for monitoring newborn brain function and at least 24-h monitoring is recommended for infants that are at risk of seizures. In infants with confirmed seizures, monitoring should be continued for 24 h after the last electrographic seizure (Shellhaas et al., 2011). Over the last 10 years, there has been an increase in demand for continuous cEEG monitoring for at-risk neonates (Wusthoff, 2016), particularly with the advent of TH and the
aEEG and EEG for the Diagnosis of Neonatal Seizures
The estimated incidence of neonatal seizures in the general population is between 1–3 per 1000 live births but with a higher incidence reported in infants born prematurely and with low birth weight (Uria-Avellanal et al., 2013). In preterm infants, reported incidence rates of seizures confirmed with cEEG or aEEG vary considerably, from 5% to 43% (Shah et al., 2010; Wikstrom et al., 2012; Lloyd et al., 2017). The reason for the disparity in these reported values is not clear, but it may reflect
aEEG and cEEG for the Diagnosis of Neonatal Encephalopathy
The commonest cause of NE is hypoxia–ischemia around the time of birth and both the aEEG and cEEG patterns seen in this condition are very different from those encountered in other types of neonatal encephalopathy. Therefore the typical findings that have been described in hypoxic–ischemic encephalopathy will be described in detail in the first instance followed by the EEG patterns encountered in other types of NE.
It is worth noting that there is much heterogeneity in studies that have used EEG
EEG Diagnosis of Neonatal Encephalopathy
Before any attempt is made to assess the background pattern of the neonatal EEG and diagnose encephalopathy in an infant, a thorough knowledge of the characteristics of the EEG in the healthy newborn infant is essential. Any patterns that deviate from this can signal an encephalopathy of varying severity. It is beyond the scope of this chapter to describe all of the normal and abnormal features of term and preterm background EEG, but a number of excellent references do exist (Pressler et al.,
aEEG in Hypoxic–Ischemic Encephalopathy
Prior to the introduction of therapeutic hypothermia, many studies described the typical aEEG patterns encountered in HIE. Most of these studies originated from very experienced aEEG centers in Sweden and the Netherlands; the classification schemes generally used for aEEG grading are illustrated in Fig. 18.14 (Hellstrom-Westas et al., 1995; al Naqeeb et al., 1999; Toet et al., 1999; van Rooij et al., 2005; Thoresen et al., 2010).
The pattern recognition method of aEEG classification, prior to
cEEG in HIE
Prior to the introduction of TH, the first studies that analyzed the role of cEEG in HIE generally recorded short duration (2 − 3h) multichannel EEG between 2 and 7 days after birth. Normal cEEG background within the first week of life was reported to be predictive of a normal long-term outcome (Sarnat and Sarnat, 1976; Watanabe et al., 1980), while significant attenuation of amplitude and burst suppression pattern (burst duration 1–10 s and interburst interval > 10 s with amplitude between bursts < 5
EEG in Other Causes of Neonatal Encephalopathy
The evolving EEG pattern seen in infants with HIE is characteristic and was discussed previously; the EEG generally improves over time (except in those with a nonrecovering inactive pattern). In a neonate with an abnormal EEG pattern that is unchanging or deteriorating, non-hypoxic ischemic causes should be suspected. EEG characteristics have been described in other causes of NE including infection, stroke, hemorrhage, brain malformation, inborn errors of metabolism and, less frequently,
Epileptic Encephalopathy
In neonatal onset epileptic or myoclonic encephalopathy, characteristic EEG changes have been well described (Yamamoto et al., 2011; Dulac, 2013; Kojima et al., 2018). Genetic causes for these conditions are constantly emerging with some genetic causes being linked to specific EEG changes, e.g., in KCNQ2 encephalopathy (Numis et al., 2014; Vilan et al., 2017).
Early infantile epileptic encephalopathy, often referred to as Ohtahara syndrome, may be caused by a number of etiologies. The EEG
Factors Affecting EEG Background Characteristics in Neonates With Encephalopathy
Several factors may influence the aEEG and cEEG other than the underlying pathology and should be considered when making any diagnosis in neonates. The administration of AEDs, in particular phenobarbitone, is associated with either general EEG amplitude depression or increased discontinuity that can last for 30–60 min. However, the rate of aEEG recovery is believed to be unaffected by AED administration (Hellstrom-Westas et al., 1995; Toet et al., 1999; ter Horst et al., 2004a; van Leuven et
Conclusion
EEG provides a unique insight into newborn brain function. It is essential for the accurate detection of seizures and to monitor the efficacy of AED treatment. In neonatal encephalopathy, EEG not only helps to assess the severity of the encephalopathy, but it can also help determine etiology. EEG provides a unique physiologic biomarker that may soon provide unique information to help instigate personalized medicine approaches for the treatment of neonatal seizures and encephalopathy.
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2021, Journal of PediatricsCitation Excerpt :Our study showed that the NE-RS may be used without the 2 aEEG items, for example, in resource-limited settings. However, it is important to note that aEEG monitoring helps to detect and treat electroencephalographic seizures and further characterize the evolution of the neurologic dysfunction beyond 6 hours of age.39,46 In our opinion, a key original aspect of the NE-RS is that the numerical assignment for each item is not symmetrical, which emphasizes the severity of neurologic dysfunction.
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