A discrepancy of 2 weeks or less between EEG age and estimated CA most likely indicates the presence of a transient central nervous system (CNS) dysfunction. If the developmental features of an EEG are immature for the stated gestational or CA and the features of the background activity in all states are normal, the following questions must be addressed: Is the age as determined by clinical evaluation overestimated or are the immature EEG features evidence of delayed maturation? The last explanation suggests that a cerebral insult may have occurred during intrauterine life. This term refers to an EEG in which the developmental characteristics in all states are immature for the reported gestational or CA. Disordered maturational development is referred to as “dyschronism” and, if present, is an important abnormality of the neonatal EEG (Hrachovy et al., 1990). In infants requiring intensive care, the EEG findings obtained within the first 24 hours after birth can provide reliable prognostic information (Pezzani et al., 1986 Pressler et al., 2001) an EEG with normal findings on the first day, or with only minimally abnormal findings, reliably indicates a good prognosis unless further brain injury occurs later.ĭyschronism: Disordered Maturational DevelopmentĪn experienced neurophysiologist can usually determine conceptional age (CA) to within 2 weeks between 26 and 33 weeks CA and within 1 week between 34 and 37 weeks CA, based upon expected developmental features (see Chapter 4) (Tharp, 1990).
With this caveat, however, some statements can be made concerning the significance of the first EEG recorded early in the course of neurological illness. Failure to recognize the importance of the time course has led to contradictory statements in the literature concerning the prognostic significance of suppression-burst activity. However, a suppression-burst pattern that is sustained over several days or that changes to a depressed and undifferentiated pattern implies a poor prognosis for recovery of brain function. Such changes drastically alter statements concerning the prognosis. However, hours later, after the infant’s physiological condition has stabilized, the EEG activity may become continuous with relatively normal background activity. For example, an EEG of an infant might show a suppression-burst pattern on the first day of life, a finding typically indicating the presence of severe brain dysfunction.
#Abnormal eeg waves serial#
Serial studies also afford greater opportunity to detect electrical seizures without clinical signs (Glauser and Clancy, 1992), which themselves may be of prognostic significance (see Chapter 7).įailure to recognize that EEG findings evolve over time may lead to a less than accurate determination of prognosis. If serial studies document the rate and character of the changes, the prognostic information will be more reliable than that obtained from a single study (Briatore et al., 2013 Chequer et al., 1992 Douglass et al., 2002 Graziani et al., 1994 Hellström-Westas and Rosén, 2005 Holmes and Lombroso, 1993 Holmes et al., 1982 Klinger et al., 2001 Kumar et al., 1999 Le Bihannic et al., 2012 Menache et al., 2002 Pressler et al., 2001 Selton and Andre, 1997 Selton et al., 2010 Takeuchi and Watanabe, 1989 Tharp 1990 Tharp et al., 1989 Watanabe et al., 1999 Zeinstra et al., 2001). The slower this change, the more severe the underlying brain abnormality. Typically, as time passes, the degree of abnormality lessens. The best estimate of the degree of damage or dysfunction can be made when the EEG documents the evolution of the abnormality over time. Ideally, the initial electroencephalogram (EEG) examination should be done within the first 24 hours after birth or after a suspected brain insult. EEG Abnormalities of Premature and Full-Term Neonates